Principles Of Operation

Seats

Principles of Operation

Front Power Seats

The 12-way seat control feature moves the seat in 12 possible directions:

- Seat forward or backward (horizontal)
- Seat front up/down (front height)
- Seat rear up/down (rear height)
- Backrest forward or backward
- Lumbar up or down
- Lumbar in or out

All 12 positions are controlled by the seat control switch attached to the outboard side of each seat. All power seat positions operate independent of the ignition state.

The front passenger power seat motors are hardwired to the seat control switch. The seat control switch supplies voltage and ground to the power seat motors to move the seat.

The driver power seat motors are controlled by the Driver Seat Module (DSM). The seat control switch supplies voltage and ground to the applicable DSM inputs. The DSM then supplies voltage and ground to the appropriate seat track motor or seat recliner motor to move the seat in the desired direction. The power lumbar circuits of the driver seat control switch are hardwired directly to the lumbar motors in the backrest and are not controlled by the DSM.

Driver Power Seat With Memory

NOTE: Verify good battery condition before diagnosing the memory seat system. Poor battery condition may interfere with memory seat operation, even if vehicle starting is possible.

The driver seat memory feature allows the driver to program a personalized seat position that can be recalled using the memory SET switch (located on the driver door) or a Remote Keyless Entry (RKE) transmitter (if associated). There are 2 memory settings possible. This only diagnoses concerns specific to the memory seat. For information on programming memory positions or recalling a stored memory position, refer to Memory Position Programming Memory Position Programming.

When memory SET switch buttons 1 or 2 are pressed, ground is supplied to the Driver Door Module (DDM) input circuits to initiate memory set and recall requests. The DDM sends request messages to the DSM using the module communication network. When a recall request is initiated, the DSM controls the power seat motors to move the seat to the stored memory position.

The DSM monitors the seat position and motor movement using sensors located in each power seat motor. The DSM supplies a shared signal feed circuit to each position sensor. Each position sensor sends a signal pulse back to the DSM to monitor the position of the seat track and seat recliner. The DSM stores the sensor position data when a SET command is received and uses this information to return the seat to the stored position when a recall command is received.

The DDM and DSM communicate DTC and other information using the module communication network. Refer to Module Communications Network Testing and Inspection for additional information concerning module communication.

When installing a new DDM or DSM, it is necessary to carry out Programmable Module Installation (PMI). Refer to Module Configuration Testing and Inspection.

Driver Seat Module (DSM) Soft Stop

To prevent unnecessary stress on the seat, the DSM auto-programs end stop points for each moving axis of the seat track and backrest. When a new driver seat track, recliner motor or DSM has been installed, operate the seat in all directions through the full range of travel to re-program all the soft stops stored in the DSM. This will avoid a premature stopping point occurrence after the repair is made. A second switch press in each direction may be required to complete motor travel.

Remote Keyless Entry (RKE) Transmitter

A RKE transmitter can be used to recall previously set memory positions, but must first be associated to that memory position. The transmitter associated with personality 1 is capable of recalling memory position 1 only. Similarly, the associated personality 2 transmitter can recall only memory position 2. Memory recall occurs when the unlock switch is depressed on the RKE transmitter.

To associate a remote transmitter to a memory position, refer to Remote Keyless Entry (RKE) Programming in Handles, Locks, Latches and Entry Systems Testing and Inspection. To diagnose a RKE transmitter concern, refer to Handles, Locks, Latches and Entry Systems Testing and Inspection.

Easy Entry/Exit Feature

The easy entry/exit feature moves the seat backwards about 50.8 mm (2 in) when the ignition key is removed or a RKE transmitter button is pressed. The DSM receives a KEY OUT message over the module communication network and commands the driver seat rearward. The DSM will cancel this operation if a valid input command is received, such as the seat control switch or memory recall request. The DSM records the seat position before moving the seat for an easy entry/exit operation and returns the seat to the recorded position when a KEY IN message is received.

This function will not operate if the feature has been disabled. The easy entry/exit feature can be disabled and enabled using the message center display menu. Refer to Instrumentation, Message Center, and Warning Chimes Information And Message Center or the Owner's Literature for instructions for using the message center.

Power Lumbar

The driver and front passenger seat backrests are equipped with a 4-way power lumbar that moves up/down and in/out. The seat control switch supplies voltage and ground directly to the power lumbar motors located in the seat backrest. The power lumbar feature operates independent of the ignition position.

The driver seat power lumbar positions cannot be set or recalled using the memory feature. No sensors are provided for these positions.

The second row bucket seat backrests are equipped with a 2-way power lumbar that moves in/out. The power lumbar switches located on the outboard seat side shields, supply voltage and ground directly to the lumbar motors located in the seat backrests.

Climate Controlled Seats

NOTICE: Avoid applying voltage directly to a Thermo-Electric Device (TED) for testing its operation. Doing so may cause damage to the TED.

Front climate controlled seats are controlled by the Dual Climate Controlled Seat Module (DCSM) mounted to the bottom of the front passenger seat cushion. Second row climate controlled seats (if equipped) are controlled by the Passenger Climate Controlled Seat Module - 2 (PCSM-2) mounted to the bottom of the LH second row seat cushion. The climate controlled seats only operate with the engine running or a scan tool can be used to command the system on/off in 15 second durations for diagnostic testing with the ignition ON and engine OFF. The front and rear climate controlled seats do not time out.

If a fault occurs setting a DTC specific to a climate controlled seat, the affected seat will be disabled by the module. When a fault causes a shutdown, the climate controlled seat indicators will turn off and the affected seat will not be operational until the next key cycle. If a temperature related DTC is set, cycling the ignition OFF and then ON again can reset the DCSM or PCSM-2 and may allow the system to function during diagnosis.

The 4 buttons (identified with seat icons), located on the Front Controls Interface Module (FCIM) and Rear Heating Ventilation Air Conditioning (RHVAC) module, activate each seat system setting and illuminate indicators on each button to indicate the operating mode, 3 indicators for high, 2 indicators for medium or 1 indicator for low. The push-buttons with the blue seat icon operate the seat cooling mode and the push-buttons with the red seat icon operate the seat heating mode. The climate controlled seat system is not equipped with auto-mode.

The front climate controlled seat button commands are communicated from the FCIM to the HVAC module and then to the DCSM using the module communication network. Similarly, rear climate controlled seat button commands are communicated from the RHVAC to the PCSM-2. Upon receiving a command, the mode status (high, medium, low or off) is communicated from the DCSM to the HVAC module and then to the FCIM which commands the indicators on or off. Likewise, the mode status is communicated from the PCSM-2 back to the RHVAC which commands the indicators on or off. The climate controlled seat system can only operate if the modules are communicating correctly on the module communication network.

Each seat cushion and backrest is equipped with a Thermo-Electric Device (TED) assembly that includes a seat blower (fan motor, serviced as an assembly with the TED). Applying voltage polarity to the TED in one direction, causes it to heat. Applying voltage polarity in the opposite direction causes the TED to cool. Cabin air is drawn through the blower and distributed to each of the TED modules located in the seat cushion and backrest. The TEDs then heat or cool the incoming air depending on the control switch settings. The air is then directed into the foam pad and manifold (part of foam pad) where it is distributed along the surface of the cushion and backrest of the seat.

Each TED contains a temperature sensor allowing the DCSM or PCSM-2 to monitor and adjust the TED temperature and the blower speed as needed to maintain seat temperature. Measuring seat temperature at different settings is possible by monitoring the DCSM or PCSM-2 PIDs using the scan tool. The temperature differences between settings is minimal and can be difficult to distinguish by feel.

The climate controlled seats can be commanded using the diagnostic tool to verify both module communication and operation of the DCSM or PCSM-2. This method may be useful for isolating a control switch concern. Refer to Module Communications Network Testing and Inspection for additional information concerning module communication. When installing a new DCSM or PCSM-2, it is necessary to carry out PMI. Refer to Programmable Module Installation (PMI) in Module Configuration Programmable Module Installation (PMI).

Climate Controlled Seat Heating Characteristics

NOTE: Temperatures are approximate.

- In the LOW setting, the DCSM or PCSM-2 is set to maintain TED temperature at approximately 46°C (115°F).
- In the HIGH setting, the DCSM or PCSM-2 is set to maintain TED temperature at approximately 65°C (149°F).
- When heating, the DCSM or PCSM-2 will vary the speed of the fans and the TED duty cycle in order to reach and maintain the temperature determined by the switch setting.

Climate Controlled Seat Cooling Characteristics

- In cool mode, the TED circuits on a seat are connected in series internally in the DCSM or PCSM-2.
- In cool mode, the TED can remove up to 8°C (14°F) from the ambient air temperature entering the system.
- When cooling, the DCSM or PCSM-2 maintains constant fan speed and TED supply voltage (duty cycle) in open loop cool mode.

Climate Controlled Seat Recovery Mode

If the temperature at one of the TEDs rises above 110°C (230°F) in the heat mode or 65°C (149°F) in the cool mode for more than 4 seconds, the DCSM or PCSM-2 will record an overtemperature DTC, remove voltage from the TEDs and go into recovery mode (blower only) for 30 seconds to cool down the TEDs. The same will occur if a temperature difference of 60°C (108°F) or greater is seen between the backrest and cushion TEDs on either front seat. The DCSM or PCSM-2 will continue to monitor the TEDs while in recovery mode. If the temperature of the TEDs does not drop to 105°C (221°F) in the heat mode or 60°C (140°F) in the cool mode after 30 seconds, the system will continue to cool the TEDs in recovery mode for up to 5 minutes. If the TEDs cool down at anytime after 30 seconds, but before 5 minutes (checked at 4-second intervals), the system will operate as normal. An overtemperature DTC will still be recorded even if the system recovers and is operating normally. Recovery mode is more likely to occur during extreme cabin temperatures with significant seat back sunload. If the system does not recover within 30 seconds in heat mode or within 5 minutes in cool mode, the DCSM or PCSM-2 will disable that seat (fault mode) and remain off until the ignition is cycled. If the DCSM or PCSM-2 detects temperature differential fault twice during the same ignition cycle, it will shutdown. If a sensor indicates a temperature below 5°C (41°F), the DCSM or PCSM-2 will shut down the TEDs and initiate system recovery mode. If the temperature continues below 2°C (36°F), the DCSM will shut down the affected seat operation.

Heated Seats

The rear 60/40 bench heated seats are controlled by a heated seat module located on the bottom of the RH second row seat. The heated seat module does not time out. The system will only function with the engine running. The rear heated seat switches are part of the Rear Heating Ventilation Air Conditioning (RHVAC) module controls but the heated seat operates independently from the climate control system. When a button on the RHVAC module is pressed, a momentary ground signal is sent to the heated seat module. When requested on, the heated seat module will decrease one setting (the sequence is high, low, off, high). In high mode, both indicators on the heated seat button illuminate. In low mode, only the low indicator illuminates.

The heated seat module supplies voltage to heater mats located in the seat cushion and backrest to heat the seat. The heated seat module monitors a temperature sensor in each cushion heater mat and regulates the seat temperature. The heated seat module is designed to remain on, heating the seat and maintaining temperature until switched off.

Normal heat cycle may require several minutes to initially warm the seat. The seat should be occupied to correctly test for normal operation. Temperature measuring devices do not provide an accurate method for testing heated seat operation as surface temperatures are subject to human and environmental characteristics. Correct testing requires heater mat resistance measurements which have tight tolerances affecting the length of time for the heater mats to reach maximum operating temperature.

The heated seat module monitors the heater output and thermistor circuits for fault detection but does not report DTCs and is not connected to the module communication network. If an open circuit or short to ground occurs, the output is disabled to the heater mats and the heated seat indicators turn off. When a fault is detected, the heated seat module only disables the affected seat and the other seat may continue to operate normally. The heated seat cannot be operated until the system is repaired and the ignition is cycled OFF and ON to reset the heated seat module from the detected fault.

The heated seat module is designed with an auto-configuration feature for use with heated seat systems equipped with dual momentary switches. This feature enables additional input circuits not intended for use on this vehicle and will cause the heated seats to operate incorrectly. If this occurs, the heated seats will both display a symptom of operating only in one mode and illuminating only one indicator. If this condition exists, a reset procedure is required to correctly configure the heated seat module for use. For diagnosis of this condition, GO to Symptom Chart. Symptom Related Diagnostic Procedures

Second Row Power Seats

NOTE: The Smart Junction Box (SJB) may also be identified as the Generic Electronic Module (GEM).

The second row bucket seats and the 40 percent of the 60/40 bench seats are equipped with a power-released latch mechanism (power-fold seat motor). When pressed, the seat control switch located on the C-pillar, supplies voltage from the SJB to the power-fold seat motor located in the base of the seat. The second row power-fold seat motor retracts a cable to release the backrest recliner latches and allows the backrest assist spring to fold the backrest forward onto the seat cushion. The power-fold seat motor continues to retract to release the seat-to floor latches and allows the spring assist strut to lift and tumble the seat forward to the E-Z entry position for third row seat access. Immediately after the seat is fully released, the power-fold seat motor returns the release cable and latches to a relaxed state, ready for manual latching. To return to a seating position, the seat must be manually latched to the floor and the backrest must be manually latched upright.

With the transmission selector in PARK and a door open, the SJB supplies a shared voltage to the system for 30 minutes using the demand lamp circuit. The voltage will be disabled 30 minutes after turning the vehicle OFF. If the demand lamp relay is disabled after 30 minutes, it can be enabled by opening any door, pressing the unlock key on the key fob or turning the ignition ON.

Third Row Power Seats

NOTE: The Smart Junction Box (SJB) may also be identified as the Generic Electronic Module (GEM).

The third row power seat system includes the following components:

- Third row power seat relay
- Power-Fold Seat Module (PFSM)
- Seat control switch
- Power-stow seat motor assembly (contains LH and RH motors and sensors)
- LH and RH power-fold seat motor and sensor assemblies (backrest)
- LH and RH latch assemblies (contains latch motor and latch switch)

The third row power seat relay coil receives voltage from the battery saver relay in the SJB (courtesy lamp circuit) and ground from the chassis. When energized, the relay switch closes and supplies battery voltage from the Battery Junction Box (BJB) to the PFSM. Sufficient battery voltage is required for PFSM operation. If battery voltage drops below 8 volts, a started seat movement will stop.

When the gear selector lever is in the PARK position and the liftgate is open, the SJB supplies voltage to the PFSM enable circuit for 30 minutes. With the ignition OFF, the SJB disables the battery saver relay after 10 minutes. The system can be re-enabled by opening any door, pressing the unlock button on the RKE transmitter or turning the ignition ON. A short to voltage on the PFSM enable circuit can result in the third row power seat being operational any time the battery saver relay is energized, regardless of gear selector lever or tailgate position.

The seat control switch contains the seat selector switch button and seat position switch buttons. The PFSM receives a voltage signal from the seat selector switch for 3 modes:

- LH seat
- RH seat
- BOTH seats

The PFSM receives voltage signals from the seat position switches for 4 possible seat positions:

- NORMAL
- FOLD
- STOW
- TAILGATE

The power-stow seat motor assemblies rotate the LH or RH seat cushion assemblies together or separately (based on seat[s] selected) and are located at the outboard seat positions. The motor assemblies contain Hall-effect sensors that indicate seat position to the PFSM. The power-stow seat motor assemblies are part of the third row seat pivot tube assembly and are not serviceable separately.

The power-fold motor assemblies rotate the LH or RH seat backrests and are located at the backrest lower outboard positions. The motor assemblies contain Hall-effect sensors that indicate seat backrest position to the PFSM. The LH and RH power-fold motor assemblies are serviceable individually.

The LH and RH latch motors receive voltage from the PFSM. The motors share a common ground supplied by the PFSM. The seat latch motors energize and release the seat latch mechanism(s) when STOW and TAILGATE positions are selected.

The latch switches are normally open and receive approximately 12 volts from the PFSM. The LH and RH latch switches share a common return circuit in series to the PFSM. The PFSM monitors the latch switch circuits to determine if the seat latches are open or closed. The latch switch is mounted to seat latch mechanism and is not serviceable. A new power seat latch must be installed.

When STOW, FOLD or TAILGATE is selected the backrest will fold forward enough to release the spring loaded headrest. If the head restraint is not folded prior to achieving FOLD, STOW or TAILGATE positions, the head restraint will become an obstruction and prevent the seat from completing the seat movement. When an obstruction is detected during any seat movement, the seat will stop, reverse movement a few inches and then stop again until the obstruction is removed. When the obstruction has been removed the seat control switch must be depressed again to reset the request. The seat will go to the home position (seat folded and latched to the floor) and then continue with the requested seat position. After the seat is repaired or a new system component has been installed, the PFSM will also need to find the seat's 'home' position before completing a selected seat position.