Second Row

Last updated: October 10, 2024

Overview

2021+ Model S has a standard 5 person seating capacity with a driver and passenger seat in the front row and a three passenger bench seat with backrests that fold flat in the rear. 2021+ Model S seats come with 3 different color options, black, white, and cream. The second row seats do not have ventilation, but do have seat heating. | | | --- | | Second Row Seats |

1. Cover 2. Heat Pad 3. Occupancy Sensors 4. Foam/Pad 5. Seat belt buckle 6. Center Seat Belt Retractor 7. Seat Frame 8. Headrest 9. Seat Audio/Microphone 10. Wire harness 11. Seat plastics 12. Back Panels
Second Row Seats

The seat sections are referred to as 40% (right-side rear seat), 60% (left-side and middle rear passenger seats), and 20% (middle rear passenger seat).

Covers

Component Description

2021+ Model S seats are available in cream, white, and, black polyurethane (PUR). This material is a leather alternative. When surfaces of the seat back contact one another, one side is a cloth material, while the other side is PUR. This is to reduce noise issues that are typical when PUR rubs against itself. Along with 3 colorways, there is an option between covers for a long range variant, and covers for a performance variant. The second row seats are perforated on the centermost panels. Performance variant second row seats have also have perforation on the inner bolsters, where the inner bolster meets the outer bolster, there is a piping for added detail and luxury.

Theory of Operation

2021+ Model S second row seat covers are secured to the foam with a combination of hog rings and hook-and-loop fastening strips. Then sandwiching the foam, the cover is attached to the upholstery support allowing the seatback to maintain shape prior to attachment to the seat frame. There is also stitch detailing within the seat to help form the shape around the foam.

Serviceability

Cleaning

Cleaning PUR seats with some conventional cleaners (especially alcohol-based) can cause performance and appearance degradation. Do NOT use products containing bleach (sodium hypochlorite). It is therefore important to clean seats with only approved cleaners. Below is a list of approved cleaners:

• Clorox NON Bleach Disinfecting Wipes
• Formula 409
• Seventh Generation NON Bleach Disinfecting Wipes

For CREAM PUR ONLY, isopropyl alcohol is the strongest solvent that can be used without damaging the seat material. Moisten a soft cloth with warm water and isopropyl alcohol and gently wipe the stain in a circular motion.

Warning

Isopropyl alcohol should not be used on Black or White PUR.

Servicing Covers

Hog rings must be installed using hog ring pliers to crimp the ring in order to securely fasten it the cover to the foam.

Hog rings are a consumable part, as with every removal they need to be cut.

Craftsmanship is extremely important when dealing with installing covers to ensure that there are no wrinkles or puckers in the material.

Foam/Pad

Component Description

The seat foam, also referred to as the seat pad provides comfort and stability to occupants.

Serviceability

If the seat foam and covers have not been installed appropriately it can feel or look as if the seat is missing foam or that the foam has collapsed. Because the foam is sandwiched between the cover and upholstery support, it is possible that it could have been misaligned during installation. In some rare cases, the way in which a customer ingresses or egresses from the vehicle can apply pressure on the outmost edge of the cover and foam, causing the foam to get caught on the upholstery support and not maintain it's full shape. This can be resolved by refitting the cover and foam.

Seat Heat

Component Description

2021+ Model S second row has heating elements in each of the cushion seating positions. The back rest only has heating elements in the left and right seat backs. The center seat, 20%, has an arm rest as the seat back which does not have a heating element.

Second Row Seat Heat

The seat heater is made up of the following components:

• High side driver
• Pulse width modulation (PWM)
• Negative temperature coefficient (NTC) thermistors
• Resistive pad

The heating element, or resistive pad, is located only in the center panels of the seat back and seat cushion, the heating element is not located in the side bolsters.

Theory of Operation

There are 3 heating temperature targets for the seats (low, medium and high). Target temperatures for both the cushion and the backrest are:

• Low (Setting 1): 28C or 82F
• Medium (Setting 2): 44C or 111F
• High (Setting 3): 60C or 140F

The seat heaters utilize PWM at 1Hz in order to reach the desired target temperature. This means pulsing the voltage at a controlled frequency. The duty cycle (width of the pulses) will be increased if the temperature read by the NTC is below the target temperature, the duty cycle can be increased all the way up to 100%, providing up to 16V. When the temperature read by the NTC is higher than the target temperature, the duty cycle can be decreased all the way to 0% providing no voltage. Due to this PWM, the voltage at the seat heater is constantly changing and varies due to ambient temperature and heat setting level.

Current travels through the resistive pad generating the heat. This resistance remains constant with a functioning seat heater.

The NTC is located only in the seat cushion, not the seat back. It is connected to 5V through a resistor on the body controller. As the temperature of the seat increases, the resistance on the NTC lowers and the voltage read at the controller goes down. If the thermistor is disconnected, the voltmeter will read 5V or 0V depending on where the disconnect occurs. At around room temperature, the voltage at the NTC should be around 3.6V.

Communication

The seat heater communicates via Vehicle bus (VEH). The seat cushion and the 60% seat back is controlled by the left vehicle controller (VCLEFT). The seat back fo the 40% seat is controlled by the right vehicle controller (VCRIGHT). Below illustrates which seat heater positions communicate on which vehicle controller.

Serviceability

The seat heater resistive pad is integrated into the seat cover and is therefore not serviceable.

The temperature felt at the surface of the seat, depends on an occupant sitting in the seat. Compressing the foam and trim with an occupant sitting in the seat allows for the occupant to fully feel the temperature provided by the seat. Factors such as a heat soaked interior, body heat from someone sitting in the seat, direct sunlight and ambient air temperatures can play a big role on the temperature readings at the surface of the seat cover.

Occupancy Sensing

Component Description

Each seat in the second row contains an occupancy sensor, resistive pad, also referred to as the seat belt reminder (SBR). The occupancy sensors are located in the seat cushion. The occupancy sensors are switches distributed throughout the cushion connected in both parallel and series.

Restive Pad (x3)

Theory of Operation

Occupancy sensing for the second row communicates to VCLEFT. The sensor itself is a simple resistive pad that can be tested with a multimeter. Occupied, the resistance should read 1kOhm. Unoccupied, the resistance should read 11kOhm.

Serviceability

Occupant sensors distributed throughout the cushion help to prevent situations where small items might trigger the seat belt reminder indicator. At the time of publishing this document, the resistive pad, or seat belt reminder, located in the second row cushion is not a serviceable component. This is due to the infrequency of which this part needs to be replaced as well as current production capability.

Frame

Component Description

The second row is comprised of two separate backrest frames. The 60% and the 40%. The 40% contains the right hand second row passenger and the 60% contains the left hand and center passenger positions, with the center position being referred to as the 20%. For 2021+ Model S, these structures are stand alone frames with the seat cushion bench being one piece that sits atop the Ancillary Bay.

Theory of Operation

The frame allows for the backrest to pivot about the bottom edge in order for the backrest to fold flat.

Serviceability

A spring is located on the outboard side of the seat, at the axis of rotation for the seatback to fold forward. This spring helps pop the seatback forward but does not cause the seatback to dump in a fold flat position.

Because the frame is a moving part, it can be the culprit to some noise issues, in these instances be sure to check all mating points to the body as well as the hinge point (axis of rotation).

Trim/Plastics

Component Description

To limit confusion during diagnosis and when talking about the seats, trim is defined as the hard plastic parts on the seat. Seat pads and covers (the textile or leather seat material) is considered seat upholstery and should be referred to as such.

In addition to the components shown in the image above, the following pieces are also considered:

• Back panels
• Switches
• Escutcheon

Theory of Operation

Back Panels

The back panels for the second row are plastic components that conceal the wiring harness and backrest shell. The back panels also have a cut outs for child seat tethers. Removing the back panel will allow access to inspect components like the latch mechanism for first steps of diagnosis.

Back Panels

Switches

The 60% and 40% sides can be adjusted via the electrical switch on the shoulders of either side, these switches can fold the seat back flat.

Outboard shoulder switches

Escutcheon

The escutcheon is the plastic bezel in which the center seat belt feeds through the backrest. The center seatbelt is the only retractor incorporated into the second row and the escutcheon acts as protection to the cover.

Escutcheon

Actuators

Component Description

2021+ Model S has a single latch mechanism that releases the seat back to allow it to fold flat. The actuator is integrated into the latch mechanism and can be serviced as one part.

The second row armrest has an actuator inside the armrest which triggers guide pins within the armrest that are lowered, allowing the armrest to fold flat.

Seat back latch

Theory of Operation

Both the seatback latch actuator and armrest actuator communicate on VCLEFT. Integrated into the mechanism is a hall effect sensor which allows the firmware to distinguish if the latch is engaged or disengaged.

Armrest

Component Description

The second row is equipped with an armrest at the center seating position. The armrest has a cupholder and a storage compartment with a lid. Between the armrest and the storage compartment is an inductive charger for two phones.

1. Compartment lid 2. Cup holders 3. Inductive charger 4. Compartment lid latch 5. Armrest switch
Armrest

Theory of Operation

The armrest communicates to VCLEFT for all of the controls. The inductive charger communicates via Local Interconnect Network (LIN). The actuator located in the armrest pulls two guide pins which allows the armrest to be free moving and only locks in the closed position.

Microphone

Component Description

There is a microphone assembly located on the left and right hand sides of the headrest in the left and right seating position in the second row. The microphones are joined together with a pigtail and then connect to the seat harness

Theory of Operation

The seat microphones do NOT communicate on VCSEATD or VCSEATP, instead they communicate directly to the car computer. The user can select noise cancellation in either the first or second row. The noise cancellation works by utilizing the door speakers in conjunction with the microphones.

Serviceability

The microphones are indicators of 2021+ Model S seats as they are the only model which offer microphones in the seat's headrests.

Fold Flat Function

Feature Description

Fold flat is referred to the position in which the seatback is completely folded down and laying on top of the seat cushion. Fold flat can occur on the 40% or the 60%.

Theory of Operation

A combination of the latch hall effect sensor and the reading from the seat belt reminder will indicate if the seat is in the folded flat position.

A short press of an electrical switch causes the actuator to run full stroke. The electrical switch for this feature can be found in these locations:

• The rear compartment.
• The outboard shoulder of the rear seat.

After the short press, there is an in-rush current spike and shortly after, a stall current spike as the actuator hits the travel limit. When the actuator has reached the travel limit, the seat back is then able to be assisted into the fold flat position. The latch mechanism pushes the seat back forward but is not enough for the seat back to dump forward on it's own. When the switch is released, and the actuator is de-energized, the actuator is spring returned back into the extended state allowing the seat back to lock into the next available position.

Fold Flat Switch - Rear Compartment

To fold flat the second row seat backs by using an interior button in the trunk, there are two window switch like buttons in the rear that can trigger either the 40% or 60% to fold flat. It sends the same signal to VCLEFT that is sent when pressing the switch in the outboard shoulders or the cushion side shield. This trunk switch utilizes one input with a voltage divider to indicate which of the seat positions needs to fold flat.

Interior fold flat switch

Fold Flat Switch - Outboard Shoulder

The 60% and 40% sides can be adjusted via the electrical switch on the shoulders of either side, these switches can fold the seat back flat.

Outboard shoulder switches

Serviceability

When folding flat, there is a potential that the seatback can make contact with the rear load floor. Interaction between the seatback and the load floor can cause creasing in either the load floor or seatback panel.

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