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Low Voltage Controllers and Wiringlink

Last updated: October 10, 2024

Circuit and Connector Diagramslink

Circuit diagrams show the path of all circuits in the vehicle, and the connector reference shows the location and pin outs of all connectors in the vehicle.

Note

Connector references and circuit diagrams can be found on the Service website.

Low Voltage Architecturelink

Power Distributionlink

The Model Y features both a low voltage system and a High Voltage system. The following devices are connected to both the high voltage and low voltage systems:

  • High Voltage Controller
  • Power Conversion System (includes DC-DC)
  • Drive Inverters (Front and Rear)
  • HVAC Compressor

All other devices in the vehicle are powered solely by the low voltage system and the low voltage system features two independent sources of power:

  • Power Conversion System (DC-DC)
  • Low Voltage Battery (LV Battery)

The DC-DC receives power from the High Voltage Battery pack and converts it to low voltage power. Power from the DC-DC and low voltage battery are merged together inside the Front Vehicle Controller (VCFRONT). This controller is the “heart” of the low voltage power distribution system and all low voltage current flows through the VCFRONT before being distributed throughout the rest of the vehicle.

While the vehicle is "awake", the DC-DC converter is the primary source of low voltage power for the vehicle and the LV battery is only discharged in the event of a DC-DC failure, or during peak loads for devices such as power steering, braking or stability control systems. When the Model Y goes to "sleep" the new Sleep bypass will turn on and connect the entire low voltage system directly to the HV Battery to supply a continuous 10.6V rather than relying on just the LV battery for power (this connection is capable of supplying up to 24V). If the LV battery is drained during Sleep the DC-DC will still turn on and recharge it, and turn off again once recharged. E-Fuses control the flow of power to each device individually like the Model 3 and can be "grouped" in firmware to create virtual power "rails" known as "Vehicle States".

Note

All Model 3 vehicles built in North America after January 1, 2020 use a Sleep bypass power supply.

High-level Vehicle States:

  • Sleep
  • Accessory
  • Drive
  • Conditioning
  • Over the Air (OTA)
  • Self-Test

Note

For more information on Vehicle States including a detailed list of the possible states, refer to the Vehicle Power States section of this document.

An E-Fuse is a transistor (MOSFET) and a current sensor. When the current through the transistor exceeds either the firmware or hardware limits, the switch opens rapidly.

Types Of E-Fuses:

  • Discrete E-Fuse
    • A MOSFET connected as a "high-side" switch with a pull-up resistor driven by an output pin configured as an open-drain to deactivate downstream loads.
    • Typical Applications:
      • High-side driven devices which draw more than 25A.
      • H-Bridge driven devices which draw more than 5A.
Discrete Style E-Fuse
  • Integrated Circuit (IC) E-Fuse
    • A MOSFET connected as a "high-side" switch, but with a separate chip integrated into its package that includes special hardware (like a current sensor, temperature sensor, thermistor, etc.) to help characterize and determine when to deactivate downstream loads.
    • Typical Applications:
      • High-side driven devices which draw less than 25A.
      • H-Bridge driven devices which draw less than 5A.

Note

For more information on E-Fuses, refer to the E-Fuses section of this document.

Powering and Controlling Connected Loadslink

Powering Loadslink

The low voltage controllers on the Model Y use the following types of integrated circuits to control the flow of power to the various loads connected to the vehicle controllers. The integrated circuits are an H-Bridge and a High-Side Driver.

High-Side Driver:

A high-side driver (shown below) is a transistor switch that can turn power on and off to a downstream load. When the switch is ON, the battery voltage is applied to the load. The current that flows depends on the load; when the high-side driver is ON it does not affect the current. Many high-side drivers feature a current sense inside the switch, and turn off automatically in the event of an over-current. A high-side driver which turns off when a specific current level is reached is called an “E-Fuse”.

For more information on E-Fuses see: E-Fuses.
High Side Driver vs. Low Side Driver

H-Bridge:

An H-bridge (shown below) is a circuit that can apply voltage across a load in two directions. It is commonly used for controlling DC brushed motors, since each direction of current flow will spin the motor in a different direction. Some examples of DC motors controlled in this way are motors in the seat, steering column, and window lift.

Note

When probing the pins for an H-bridge, make sure to measure across the two pins of the load. If only measuring from one of the H-bridge pins to ground, the readings may not match what the load is seeing.
H-Bridge

Harnesses and Pass-throughslink

In addition to the use of traditional low voltage harnesses, the Model Y also makes use of pass-through style connections similar to the Model 3 in order to reduce the number of the inline connectors and wire splices required to connect the various controllers in the vehicle. To reduce the number of splices on CAN harnesses, the Model Y has more pass-throughs on the left and right controllers compared to Model 3.

A pass-through style connection is just a metal trace on a printed circuit board (PCB) on one of the vehicle's low voltage controllers and acts like a wire harness extension. This trace does not touch any other circuitry on the PCB. It is just a "wire".

Example of a Pass-through vs. Traditional Inline Connector:

  • By using traditional inline connectors the design requires connectors A, B, and C along with inline connectors 1 and 2.
  • By using pass-throughs, the design only requires connectors A, B, and C. Inline connectors 1 and 2 are not required.
Traditional Inline Connectors vs. Pass-throughs
Audio and Airbag Pass-throughs
  • Red Lines Shown Inside Controllers - Pass-throughs
  • Black Lines - Signal Carrying Wires
CAN Passthroughs
Lines Shown Inside Controllers - Pass-throughs

Note

For more information on CAN and vehicle communication architecture, refer to: Communication Architecture.

Cut-Loopslink

Power wires for the High Voltage pack contactors and Restraint Control Module (RCM) are routed throughout the vehicle into two loops of wire. After a crash event, first responders (Firefighters, EMTs, etc.) can cut these wires to disconnect the High Voltage Battery pack from the vehicle, and disable airbags.

Note

The use of single cut-loop connectors makes the vehicle's low voltage system more serviceable because the Ancillary Bay connector under the rear seat no longer has to be disconnected.
First Responder Cut-Loops

Controllerslink

Front Vehicle Controller (VCFRONT)link
1. J1 / X021 / Thermal - Batt and PT Coolant Pumps, EXV, 8 Way Valve, Temp and Level Sensors.
2. J6 / X014 / THIC B+ - VBAT (LV Battery), VCLEFT, EPAS 1.
3. J5 / X015 / THIC DC-DC - PCS, VCRIGHT, EPAS 2.
4. J2 / X012 / 5P - 5 Pin High Power (iBooster, Windshield Wiper, Autopilot 1).
5. J4 / X010 / Main - HeadlLights, Frunk Latch, MCU, HCU/ESP, Louver, Radar, Front DI, Homelink, Li-Ion LV Battery.
6. J3 / X011 / 7P High Power - HCU/ESP, Condensor Fan, Autopilot ECU 2

Power Distributionlink

The Front Vehicle Controller is located in the front of the vehicle, under the hood, directly behind the low voltage battery. The controller is powered by the low voltage battery and the PCS (Power Conversion System), depending on Vehicle State. The front controller provides power delivery to the entire low voltage system and it does so through the following E-Fuses: MCU, VCLEFT, VCRIGHT, EPAS, Autopilot, HCU/ESP/ABS, iBooster, PCS. The front vehicle controller is an always-on component, meaning it receives power during Sleep and is "always-on".

Communicationlink

The front vehicle controller supports both CAN and LIN communication with information being relayed to devices connected to the controller by a combination of direct I/O, CAN, LIN, and pass-through connections (Table 4. lists all of the loads connected to the VCFRONT). The front vehicle controller is connected to and communicates on both the Vehicle (VEH) and Private (a.k.a Party) CAN buses. Commands from VCFRONT that are consumed by electronic control units (ECUs) on the chassis (CH) CAN bus are forwarded by the Gateway (GTW).

For more information on the vehicle communication architecture refer to: Communication Architecture.

Left Vehicle Controller (VCLEFT)link
1. J2 / X030 / Body 1 - VCSEC, BLE Endpoints, Chargeport ECU.
2. J6 / X037 / Frunk - CAN and CAN Passthrough, Front Impact Sensors, RCM.
3. J11 / X038 / HVAC - HVAC Blower Motor.
4. J10 / X035 / Dash - Brake and Tail Lights, EPBL, TPMS, Brake Switch, Liftgate Struts.
5. J9 / X032 / Front Seat - Front Seat Heater, Front Seat Track and Tilt Motors, Driver Airbags.
6. J7 / X033 / 7P Front Door - Mirror Tilt and Fold Motors, Door Latche, Door Switchpack, Front Window Lift Motor.
7. J5 / X039 / Body 3 - Liftgate Strut Encoders, 2R Seat Motors and Fold Flat Switches, LV Aux Socket
8. J1 / X036 / Power - Power Feed From VCFRONT
9. J4 / X031 / Body 2 - Brake and Tail Lights, Trunk LED, EPBL, 2R Center OCS, Rear Window Lift Motor, Brake Switch.

Power Distributionlink

The left vehicle controller gets power from the Front Vehicle Controller, depending on Vehicle State, via a dedicated high current E-Fuse or Standby shared E-Fuse. The controller manages the majority of devices on the left hand side of the vehicle through multiple internal microcontrollers.

Information is relayed to devices by a combination of direct I/O, CAN, LIN, and pass-through connections. The left vehicle controller is an always-on component, meaning it receives power during sleep and is "always-on".

Communicationlink

The left vehicle controller supports direct I/O, CAN, and LIN communication. The main microcontroller and Electronic Park Brake (EPB) microcontroller communicate on both Vehicle and Private CAN, they are distinct devices even though they are on the same PCBA. The LH controller communicates with the steering wheel ECU, Headliner ECU, Lumbar ECU via LIN while items such as the switchpack and door handles are direct I/O controlled.

For more information on the vehicle communication architecture refer to: Communication Architecture.

Right Vehicle Controller (VCRIGHT)link
1. J6 / X057 / Frunk - eFuse Lockout, Front Ultrasonics, RCM, Standy Power, HV Contacors, CAN.
2. J2 / X050 / Body 1 - Brake and Tail Lights, Rear Ultrasonics, Trunk Latch, Rear Door Handle and Window.
3. J12 / X060 / Body 3 - Rear Glass Heater.
4. J5 / X059 / Body Y - 3R Seats, Liftgate Switch and LED, Trunk Latch.
5. J7 / X053 / Front Door - Mirror Tilt and Fold Motors, Door Latche, Door Switchpack, Front Window Lift Motor.
6. J9 / X052 / Front Seat - OCS, Seat Heater, Seat Track and Tilt Motors, Driver Airbags.
7. J10 / X055 / Dash - HVAC Vanes, Glovebox, PTC Heater, RCM, eCall, Footwell LED.
8. J11 / X058 / HVAC - HVAC Mode Duct, HVAC Bleed, HVAC Temp Sensor.
9. J1 / X056 / Power - Power Feed From VCFRONT.
10. J4 / X051 / Body 2 - Rear DI Oil Pump, Rear Window Lift Motor, Rear Door Latches and Switches, THS.

Power Distributionlink

The right controller is powered by the Front Vehicle Controller, depending on Vehicle State, via a high power dedicated E-Fuse or Standby shared E-Fuse. The controller manages the majority of devices on the right hand side of the vehicle via multiple internal microcontrollers. Information is relayed to devices by a combination of direct I/O, CAN, LIN, and pass-through connections. The right controller is an always-on component, meaning it receives power during sleep and is "always-on".

Communicationlink

The right vehicle controller supports direct I/O, CAN, and LIN communication. The main microcontroller, and EPB microcontroller communicate on both Vehicle and Private CAN. The Ultrasonic microcontroller communicates on Chassis and Park CAN. The microcontrollers are distinct devices even though they are on the same PCBA. The RH controller communicates with the Lumbar, and Light/Humidity ECUs via LIN. Items such as the switchpack and door handles are direct I/O to the controller.

For more information on the vehicle communication architecture refer to: Communication Architecture.

Trailer Light Controllerlink

Overviewlink

The Model Y offers a trailer package option that can be installed during manufacturing of the vehicle, selected during purchasing, or with a Service visit installation. All the fuses, drivers, and logic to support a trailer are fully integrated into the VCLEFT (shown below).

Model Y Trailer Light Controller Architecture

Trailer Connectorslink

The trailer light requirements differ between North America, Europe and Australia. Below are images of the two supported connectors (7-Pin and 13-Pin) and pin-outs showing how the various loads are connected.

Note

The 12V AUX load ouptut can only supply low currents.
7-Pin Trailer Connector (North America)
13-Pin Trailer Connector (Europe)

Trailer Stateslink
13-Pin Trailer Connector

E-Fuseslink

Overviewlink

An electronic fuse (E-Fuse) is a solid state switch, or a transistor and a current sensor. When the current through the transistor exceeds either the firmware or hardware limits, the switch opens rapidly. The E-Fuse replaces the traditional relay and fuse combination. It allows for better handling of electrical faults and protection of harnesses if a fault does occur. Traditional fuses can take several seconds to trip while an E-Fuse can interrupt current flow in a matter of milliseconds. In order to use E-Fuses, detailed electrical behavior for each load is required in order to differentiate between a false positive and a true fault. E-Fuses also significantly impact the concept of "power rails" because they allow for firmware-controlled virtual groupings of individual E-Fuses into "virtual" power rails which we refer to as "Vehicle States".

Note

The Model 3 and Model Y do not use traditional fuses. They only use E-Fuses.

Operationlink

An E-Fuse functions like a traditional fuse (opens circuit when too much current is flowing through it), except it reacts faster.
E-Fuse Overview

Trippinglink

If an E-Fuse trips, a fault signal will be read by the microcontroller. Depending on the type of load the E-Fuse is connected to, the construction of the E-Fuse, and the Vehicle State when the fault occurs, the behavior may be to enter either auto-retry or latch-off mode. Some E-Fuses may only latch-off, some always auto-retry, and some are configurable. In Tesla applications, most fall under the configurable category.

After an E-Fuse trips, Tesla firmware does not immediately try to re-enable the E-Fuse. The design intent is for the E-fuse to only trip when an electrical fault occurs, thus the E-Fuse should only be re-enabled after the electrical fault has been repaired by Service. A few exceptions to this statement exist:

  • Capacitive inrush problems:
    • In this scenario, firmware quickly re-enables E-Fuses to precharge downstream capacitive loads.
  • User accessible ports such as the LV power socket, USB ports, and the trailer light ECU can be reset by cycling control to those outputs to recover them.

Auto-Retry Behavior:

  • The intent of the "Auto-Retry" is to have Tesla firmware intervene when a fault is detected. Using the fault signal sent to the microcontroller, firmware will immediately disable the E-Fuse until pre-defined conditions are met to re-enable the E-Fuse.

  • When an E-Fuse is capable and configured for auto-retry, it will turn off, wait a period of time, then attempt to turn back on for a period of time as determined by firmware.

Latch-Off Behavior:

  • When a latch-off E-Fuse trips, it will turn off and remain off until firmware resets the E-Fuse. An E-Fuse reset is typically achieved by toggling the enable signal off-on. The enable signal will always be reset in the event of a power on reset of the microcontroller, unless the enable line is locked out.

Lock-Out Behavior:

  • There are specific conditions where firmware prevents toggling of the enable line via separate protection circuitry (this is only done for E-fuses deemed drive critical, not all E-fuses). This is true in the Drive state, where it is unacceptable for firmware to actively turn off any E-Fuse. This does not mean the E-Fuse cannot trip, only that the microcontroller cannot turn off or toggle the E-Fuse enable signal. This lock-out persists on the vehicle controllers even through a reset of the main microcontroller. The only way to unlock the enable signal is to leave the Drive state.
Master Slave Purpose
Right Controller Front Controller An I2C port expander exists between the front vehicle controller micro and the enable pins of drive-critical E-Fuses. When the vehicle shifts into Drive, the right controller holds the port expander in reset which "locks in" the port expander output states. This prevents the front vehicle controller micro from accidentally turning off drive-critical E-Fuses during Drive.
Front Controller Power Conversion System (PCS) DC-DC The DC-DC converter sources up to 193A into the front vehicle controller. If current flows from the DC-DC converter into the front vehicle controller prior to the front vehicle controller enabling the DC-DC E-Fuse, the body diodes of the E-Fuse FETs could experience a thermal event. Therefore, this lockout exists to prevent the DC-DC converter from being enabled until the front vehicle controller E-Fuse is fully enabled.
Left/Right Controller Secondary and Primary Micro Left/Right Controller Secondary and Primary Micro The Primary and Secondary micros must both agree to apply or release the Electronic Park Brake (EPB) before the brake can be actuated. They also must agree on power states for the High Voltage Processor (HVP), contactor power, and 12V power to the Rear Drive Inverter.

Other lockout circuits that exist in the Model Y, but are not directly associated with E-Fuses:

  • Restraint Control Module → High Voltage Controller (ENS)
  • Charge Port → Drive Inverter (Proximity).
    • This lock-out is done.
  • Brake and Accelerator Pedal → Drive Inverter.
  • This lock-out is done.
  • High Voltage Interlock Loop (HVIL).
  • Front Cut Loop (containing Restraint Control Module and High Voltage Contactor power feeds).

Types Of E-Fuseslink

External FET (Discrete):

A discrete E-Fuse uses a MOSFET connected as a "high-side" switch with a pull-up resistor driven by an output pin configured as an open-drain to deactivate downstream loads. A high-side driven switch means that the load is after the switch, with one end of the load tied to ground. Conversely, a low-side driven switch is the opposite, meaning the switch is after the load (before ground), with one end of the load tied to power.

  • Typical Applications:
    • High-side driven devices which draw more than 25A.
    • H-Bridge driven devices which draw more than 5A.
  • Discrete E-Fuses are typically comprised of multiple components, including:
    • Gate drive circuit (IC or discrete).
    • Charge pump (can be integrated into a gate drive IC, or be external).
    • Current sense amplifier (can be integrated into a gate drive IC, or be external).
    • External N-channel FET (field effect transistor).
    • External low-side flyback diode or low-side FET.
    • External current sense resistor.
  • Inputs typically include:
    • Enable.
    • Reset.
    • Misc settings such as gate drive current, VDS overcurrent threshold, current-chop threshold.
  • Outputs typically include:
    • High-accuracy current sense.
    • Fault.

Internal FET (Integrated Circuit):

An integrated circuit E-Fuse uses a MOSFET connected as a "high-side" switch, but with a separate chip integrated into its package that includes special hardware (like a current sensor, temperature sensor, thermistor, etc.) to help characterize and determine when to deactivate downstream loads.

  • Typical Applications:
    • High-side driven devices which draw less than 25A.
    • H-Bridge driven devices which draw less than 5A.
  • This is just contains an off-the-shelf integrated circuit which typically consists of:
    • An N-channel FET (field effect transistor).
    • Charge pump (used to increase, or decrease voltage across a load).
    • One or more temperature sensors.
  • Inputs typically include:
    • Enable.
    • Reset.
  • Outputs typically include:
    • Low-accuracy current sense.
    • Fault.

Types Of Fault Protectionlink

Current-Based Fault Protection:

Current-based fault protection measures a voltage drop across an external current sense resistor to determine current flow. If the current exceeds a configurable threshold, the E-Fuse opens the circuit. This type of protection is most often associated with discrete E-Fuses. An E-Fuse with current-based protection is relatively easy to match with the harness to make sure that there is adequate protection, but are more difficult to engineer to prevent false trips as extensive characterization of the downstream loads is required.
Current-Based E-Fuse Fault Detection

Discrete high-side E-Fuses typically feature two levels of overcurrent protection:

Short-Circuit Overcurrent Protection:

If current flowing through the E-Fuse exceeds the “Short-Circuit Overcurrent Threshold,” the E-Fuse will trip within 1 millisecond indicating a low-resistance "hard" short circuit has occurred.

Steady State Overcurrent Protection:

Some devices draw large bursts of current for short durations. To ensure these devices function properly, the E-Fuse allows current to exceed the “Steady-State Overcurrent Threshold,” but only for a short period of time. However, the MOSFET will overheat if current of magnitude “A” flows through them for an extended period of time. Therefore, if the “Steady-State Overcurrent Threshold,” is exceeded for an extended period of time, the E-Fuse will trip.

Examples of devices that use these E-Fuses include:

  • The "Big 7" E-Fuses on the front vehicle controller (iBooster, ESP, PCS, VCLEFT, VCRIGHT, EPAS).
  • High-current H-Bridges (seat motors, steering column motors, parking brake motors, windows lift motors).

Temperature-Based Fault Protection:

Temperature-based fault protection is usually associated with integrated circuit style E-Fuses which feature an internal thermistor (a resistor whose resistance is dependent on temperature). If the thermistor becomes too hot, the E-Fuse opens the circuit. These devices are typically not configurable. This type of fault protection is more tolerant to loads and conditions that are not fully characterized, but are affected by ambient temperature.

On-board Diagnostics (E-Fuse Self-Checks)link

Self-check steps for E-Fuse with no upstream turn off path include:

  1. Measure voltage on output of E-Fuse (verify E-Fuse is off).
  2. Turn on E-Fuse.
  3. Measure voltage on output of E-Fuse (verify E-Fuse is on).
  4. Turn off E-Fuse via fault injection.
  5. Measure voltage on output of E-Fuse (verify E-Fuse is off).
  6. Turn on E-Fuse.

The purpose of these "self-checks" is to verify the E-Fuses can be turned off properly prior to shifting the vehicle into Drive.

For more information on how E-Fuses are utilized, refer to HV Architecture Power Electronics section.

Vehicle Power Stateslink

Overviewlink

The E-Fuses in the VCFRONT control the flow of low voltage power throughout the vehicle and are "grouped" together in vehicle firmware to create these virtual power "rails" known as "Vehicle States". The table below lists all the virtual power states the VCFRONT can inhabit.

Power State State Description
Accessory The Accessory state is intended to support in-vehicle entertainment and HVAC features.
Accessory Plus Intended for the manufacturing environment, when the VCFRONT is not in Drive. If UDS security access is granted, the VCFRONT shall enter Contactors Open (self-test), Accessory (self-test) or Accessory Plus (self-test) states for a fixed timeout based on the input parameters of the routine.
Conditioning The Conditioning state is intended to support (but not limited to) vehicle preconditioning, postrun (cooling PT), maintaining pack temperature, LV support, heating to charge, charge, and Sentry mode.
Drive Whenever PNRD is available on the UI the vehicle is in a drive state even if the vehicle is not in the Drive Gear.
HV Up Standby HV Up Standby is an intermediate state that is used to evaluate which HV Up state VCFRONT should transition to, or if it should transition to LV Awake.
LV Awake The LV Awake state is intended to only power ECUs essential for system monitoring. Upon entering LV Awake, the VCFRONT will re-enable its internal switched rails and re-initialize its brushless motor drivers (battery pump, powertrain pump, and radiator fan).
Sleep Shutdown Upon entering Sleep Shutdown, the VCFRONT turns off the high current power feeds to all permanently powered devices if the current on the Sleep bypass e-Fuse is < 3A.
Sleep Standby In this state, the VCFRONT executes Sleep Shutdown procedures and sends commands to put busses to sleep.
LV Shutdown In this state all switched power ECUs are turned off.
OTA In this state, the VCFRONT will make all E-Fuse channels available to control via UDS for use during firmware updates.
Battery Post Wake In Battery Post Wake, the VCFRONT will not turn on any loads except one that allows the frunk latch to actuate and disable all reverse battery protection FETs.

LV State Machinelink

The LV state machine could be considered the master state machine of the Model Y, since it powers the Front Vehicle Controller. Each state has implications on power distribution to vehicle components, as well as influencing the state machines of other controllers, and inhibiting or triggering certain functions or processes. Below are some of the key LV state machine states, with brief descriptions relating to power management and examples of inhibiting or triggering processes.

Note

The transition examples are not the complete list, and there are intermediate states not captured in this section due to the complexity of the state machine.

Note

To learn more about state machines in general, a good starting point for research the term "Finite-State Machine".
LV States

Power State Truth Tablelink

The Power State Truth Table gives record of which ECUs are powered in the core LV State Machine "Vehicle States."

  • 1 = Powered
  • 0 = Shut down
  • Requires Warning = 1
    • ECUs that have a shut down procedure require a fixed amount of time before the power feed can be safely cycled.
  • C = Conditional
    • Some ECUs may be on in Vehicle States when they are normally not ON, due to requiring time to shut down, or because of a keep power request. An example is the Restraint Control Module in a crash event.
ECU Signal Drive Accessory Conditioning LV Awake LV Shutdown Sleep Shutdown Requires Warning Warning Time
SWC VCLEFT_swcLVState 1 1 1 1 0 0 0
VCLEFT VCFRONT_vcleftHiCurrentLVState 1 1 1 1 1 0 1
VCRIGHT VCFRONT_vcrightHiCurrentLVState 1 1 1 1 1 0 1
Headlight ECU 1 1 1 1 0 0 1
OCS VCRIGHT_ocsLVState 1 1 0 0 0 0 0
HVAC Sensor 1 1 0 0 0 0 0
UI [GTW/Display] (high current) VCFRONT_uiHiCurrentLVState 1 1 1 1 1 0 1
UI (Audio) VCFRONT_uiAudioLVState 1 1 1 0 0 0 0
Tuner VCRIGHT_tunerLVState 1 1 1 0 0 0 0
External Amplifier VCRIGHT_amplifierLVState 1 1 1 0 0 0 0
Front USB 1 1 1 0 0 0 0
Rear USB 1 1 1 0 0 0 0
Homelink 1 1 1 1 1 0 0
Autopilot [Parker, Pascal] (high current) VCFRONT_das1HighCurrentLVState 1 1 1 1 1 0 1
Autopilot [Parker, Aurix] (high current) VCFRONT_das2HighCurrentLVState 1 1 1 1 1 0 1
Radar VCFRONT_radcLVState 1 0 0 0 0 0 0
Radar Backup Power 1 0 0 0 0 0 0
Park Assist VCFRONT_parkLVState 1 1 1 1 1 0 0
ESP VCFRONT_espLVState 1 C C C 0 0 0
EPAS 1, 2 (High Current) VCFRONT_epasLVState 1 0 0 0 0 0 1 5s
RCM VCLEFT_rcmLVState/VCRIGHT_rcmLVstate 1 C C C 0 0 0
TPMS VCLEFT_tpmsLVState 1 0 0 0 0 0 1
iBooster (power and wake line) VCFRONT_iBoosterLVState 1 1 0 0 0 0 0 49s
ESP Motor VCFRONT_espLVState 1 0 0 0 0 0 0
PCS 1 1 1 1 1 0 0
DIV CLEFT_diLVState C C C 0 0 0 1 400ms
DIS VCFRONT_disLVState 1 0 0 0 0 0 0 400ms
Oil Pump (Rear) VCRIGHT_rearOilPumpLVState 1 C C 0 0 0 1
Oil Pump (Front) VCFRONT_oilPumpFrontLVState 1 0 0 0 0 0 0
PTC VCRIGHT_ptcLVState 1 1 C 0 0 0 1
HVAC Compressor VCFRONT_hvacCompLVState 1 1 C 0 0 0 1
Lumbar VCLEFT_lumbarLVState/VCRIGHT_lumbarLVState 1 1 0 0 0 0 0
Windshield Wiper ECU 1 1 0 0 0 0 0
SCCM VCLEFT_sccmLVState 1 1 0 0 0 0 1 12s
CP (high current) VCLEFT_cpLVState 1 1 1 1 1 0 0
HVC (high current) VCRIGHT_hvcLVState 1 1 1 1 1 0 0
HV Contactors 1 1 1 1 1 0 0
Air Suspension VCFRONT_tasLVState 1 1 1 1 1 0 0
VBAT Fused Low Current 1 1 1 1 1 0 0
Rear Drive Inverter Discharge 1 1 1 1 1 0 0

Sleep Architecturelink

During the vehicle Sleep state, many low voltage devices are turned off to reduce loss of range when the vehicle is not in use. The chart below lists the ECUs that receive Standby power during Sleep, and which low voltage controller powers them.

Front Controller - Gateway - Autopilot - Power Steering (EPAS) - Battery Backed Siren (Europe)

Left Controller - Security Controller - Left and Rear Bluetooth Low Energy (BLE) Endpoints - Charge Port - Intrusion Sensor (Europe)

Right Controller - High Voltage Processor (HVP) - Right BLE Endpoint

Sleep Sequencelink

The vehicle will go to Sleep if it is not in use and there are no controllers that are setting a keep awake reason. Examples of keep awake reasons that are not related to direct user interaction (vehicle occupants, driving) are as follows: LV Support request, Charging, Preconditioning.

When all the keep awake reasons are listed as NONE, the front vehicle controller and Gateway will send a "GoToSleep" message on all the CAN busses. When an ECU receives this message, it ends most processes and enters a low power state and becomes "CAN quiet". In this state, each ECU suppresses CAN transmits that are not wake up reasons, and receives or listens for CAN traffic from other ECUs in order to know when to wake up or abort Sleep. The final message to be transmitted is the command for the VEH CAN bus to go to Sleep.

In order for the vehicle to truly sleep, the low voltage battery current, measured by the Intelligent Battery Sensor (IBS) that is on-board the front vehicle controller, must first fall below 3 Amps. This will trigger the front vehicle controller to deactivate the high power E-Fuses it manages. The front vehicle controller then waits until the 12V Battery current drops below 500 mA before it turns off non-essential portions of itself, shutting down internal 12V and 5V rails. Finally, the microcontroller goes into a low power state.

During Sleep, there is some LV current draw through the Sleep bypass. This average current is reported after the vehicle wakes up by VCFRONT_sleepCurrent. While 500 mA is the minimum threshold to Sleep, it is high enough to drain the LV Battery to the point where it requires support relatively quickly. Ideal vehicles have an average sleep current of about 75 mA, while the majority of vehicles draw around 120-130 mA. There are many factors that affect LV current draw, the largest issues being 3rd party devices tapping into the Sleep Standby Supply (this will significantly throw off the LV Battery charging algorithm).

Waking From Sleeplink

The Wake state inputs to the vehicle come from always-on loads that send a message to any controller connected to the CAN bus. The wake reason can be determined by inspecting vehicle CAN logs. Each controller that is capable of waking the vehicle will update its "wakeUpReason" signal when the controller wakes from Sleep and the Gateway resumes CAN logging.

The front vehicle controller will wake the vehicle if one of the following events occurs:

  • The front controller detects the low voltage battery needs to be charged.
  • An always-on load sends a message to the front controller to wake the vehicle, for example:
    • The security controller detects a key
    • A door handle is pulled
    • SMS poke
  • Current flowing through the battery monitoring integrated circuit exceeds a set threshold (set in firmware by the front vehicle controller micro).

Note

A nearby phone key will not wake up the vehicle until the door handle is pulled.

Wake Inputs

Signal Controller Type Reason
Interior Door Handle VCLEFT/VCRIGHT User-Accessible Allows occupants to exit the vehicle
Exterior Door Handle VCLEFT/VCRIGHT User-Accessible Allows occupants to enter the vehicle
Brake Pedal VCLEFT/VCRIGHT User-Accessible Allows occupant to wake the vehicle by pressing brake
Latch Status (Door,Frunk, and Trunk) VCLEFT/VCRIGHT User-Accessible Allows the latches to wake vehicle in the event of break-in
Exterior Trunk Switch VCRIGHT User-Accessible Allows occupants to enter the vehicle
Interior Frunk Switch VCFRONT User-Accessible Legal requirement
Hazard / SOS Button Front OHC User-Accessible Legal requirement
Intrusion Sensor / Battery Siren (Europe Only) Rear OHC/Battery Siren User-Accessible Allows vehcile to wake in the event of a break-in
Chargeport Button / UHF Chargeport User-Accessible Allows user ability to wake vehicle for charging
Front Access Post VCFRONT User-Accessible In the event of a dead LV Battery, when the user apply low voltage to the front access post, the vehicle will wake
Sleep Bypass / 12V Battery Monitor VCFRONT User-Accessible If a firmware or hardware fault occurs during Sleep, resulting in an excessive amount of current being drawn, the front vehicle controller micro will wake up, attempt to resolve the problem, and put the vehicle back to sleep.

Communication Architecturelink

Overviewlink

The various controllers on the Model Y communicate with each other via one of the following:

-CAN (Controller Area Network) - Used when high bandwidth, or low latency are required by an ECU. - LIN (Local Interconnect Network) - Used when high bandwidth. or low latency are not required by an ECU. - Video (Coaxial).
Model Y Communication Architecture

Bus Mappinglink

Model Y CAN bus networks are mapped to different ID numbers depending on where they connect to the microcontroller within the gateway.

Bus ID Bus Name
2 Party
6 Chassis
7 Vehicle

CANlink

Overviewlink

A Controller Area Network (CAN) is a durable low cost communication standard designed to allow any device on the network to communicate with any other device without the need for a host computer. Each device (ECU on a CAN network is connected by 2 signal-carrying wires (CAN-HIGH, CAN-LOW) with each wire carrying a complimentary signal waveform used to signify if the signal being transmitted is a logical 1 or 0.

Trasmitting and Receiving Datalink

First, a device connected to an ECU (like a sensor) detects some value. This value is then stored in the microcontroller input memory on the ECU. If this value is also required for another ECU connected to the network, it will be sent over the CAN bus. Before this value can be sent, it is first copied to the transmit memory of the ECU. From there, the information goes to the transmit mailbox of the CAN module. If a current value is located in the transmit mailbox, it is indicated by the transmit flag (flag is raised).

Once the message is sent to the CAN module, it then checks via the Receive (Rx) line whether the bus is active (i.e. whether information is in the process of being exchanged on the network). If necessary, it waits until the bus is free before sending the message over the bus. All stations connected to the bus then receive the message as it travels over the Receive (Rx) lines to the receive areas of each of the CAN modules. All connected stations receive the message sent by the sensor and using the CRC checksum (Cyclic Redundancy Check) they detect whether any errors have occurred in transmission. When a message is sent, a checksum is generated from all the bits and is included in the transmission, and the receivers all calculate the checksum from all the bits received using the same protocol. Once the received checksum is compared with the calculated checksum and no error are found, all the stations send an acknowledgement to the transmitter.

Finally, the correctly received message goes to the acceptance section of the associated CAN modules. From there, a decision is made whether the message is necessary for the function of the related control unit. If needed, the message is placed in the receive mailbox. Otherwise, it is discarded.
CAN-Bus Transmitting and Receiving Data
  • CAN Transceiver - The transceiver is a transmitter and receiver amplifier which converts the serial bit stream (logic level) of the CAN module into voltage values and vice versa.
  • CAN Module - The CAN module is what controls the data transfer process for CAN messages and is divided into two sections, the receive section and the send section. The CAN module is connected to the control unit via a receive mailbox or the send mailbox which correspond to memory locations on the microcontroller chip.
  • ECU - The ECU is the device that is receiving and processing signals from things like sensors and actuators and is the top level device in the stack. For Example: The ESP, iBooster, EPB, etc.

Error Managementlink

Since each message transmitted on the bus is recieved by each node on the bus, each node can check the validity of all the messages and post an error on the bus if a message is not valid. The tracking of these Tx (Transmit) and Rx (Receive) errors is how a CAN bus manages communication errors on the network. Using the broadcast process described in the section above, any device connected to the network that detects an error immediately notifies all other devices on the network by sending an error message called an "error frame," and the current message is then rejected by all devices on the network. This is then followed by an automatic repeat of the last transmission. If transmission continues to repeat due to continuously detected errors, an integrated error counter on each station will increase to track the error. If the preset threshold value for the error limit is exceeded (equivalent to 32 repeat transmissions), the affected ECU is informed and the CAN bus is switched off.
CAN Bus Error Counters

Troubleshooting Issueslink

Step 1: Measuring the resistance on the bus

The most common CAN bus issue is either too much or too little termination resistance. In a low speed CAN network, each device connected to the bus typically has a 120 ohm resistor. In a high speed CAN network (which is what Tesla uses), only the ends of the main loops have a 120 ohm resistor. If the bus only has 2 resistors, the measured resistance between CAN-H and CAN-L will be 60 ohms. This is because there are two 120 ohms resistors connected in parallel. Conversely, if the bus has three 120 ohm resistors in the main loop, it will measure 40 ohms. With four resistors the measured resistance will be 30 ohms.

CAN Bus

Note

The CAN bus must be powered down in order to retrieve accurate resistance measurements.

The reason the resistance measurement requires the CAN bus to be powered down is due to the way a Digital Multi-Meter (DMM) measures resistance. A DMM uses a constant current source to drive a known and fixed amount of current through the resistor that is being measured. In parallel, the voltage drop across the resistor is measured. The resistance is then calculated using Ohm's law, V= I*R, solving for R. If there is another voltage source applied to the resistor, there will be an unknown current from the bus going through the resistor, changing the voltage drop and rendering the measurement by the DMM completely invalid.
Desired Operation
Incorrect Measurement

CAN Bus Termination

Rear Wheel Drive All Wheel Drive
Controller Vehicle Private Chassis Vehicle Private Chassis
VCFRONT - 120 - - 120 -
VCLEFT 120 - - 120 - -
VCRIGHT 720 720 - 720 720 -
Drive Inverter 120 120 - 120 120 -
Drive Inverter Slave - - - 720 720 -
Infotainment Computer - - 120 - - 120
Electronic Stability Program - - 120 - - 120
Measured Bus Resistance (ohms) 55.38 55.38 60 51.43 51.43 60

Step 2: Measuring the voltages

The voltage on a CAN-High wire usually fluctuates between 2.5V and 3.5V while the CAN-Low wire usually fluctuates between 2.5V and 1.5V. The easiest way to see these voltage fluctuations is with a picoscope, but if a picoscope is unavailable, it is possible to measure the average voltage directly with a multi-meter. The measurement should be around 2.2V for CAN-Low and 2.7V for CAN-High.
CAN Bus Voltages

Step 3: Checking the CAN bus load

There are no clear-cut rules for what the max bus load should be, but in general once the bus load increases beyond 70%, there is a possibilty of data loss, or communication errors.

LINlink

A Local Interconnect Network (LIN) is a low cost alternative to CAN, if speed, or fault tolerance are not critical. Each ECU on a LIN network is connected to master node with a maximimum number of 16 nodes being connected to one master. Unlike CAN, devices on a LIN network are connected by one signal-carrying wire instead of two and operating at LV bus voltage instead of 5V like CAN. If a LIN bus is connected to a CAN bus, it is usually connected via a master LIN node.
LIN Network
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