Principles of Operation

Seats

Principles of Operation


Driver and Passenger Power Seats Without Memory

The 10-way seat control feature moves the seat in 10 possible directions: the seat can be moved forward or backward and the front and back of the cushion can be moved up and down independently. The backrest of the seat can be moved forward and backward, and the lumbar can be moved in and out. All 10 positions are controlled by one switch. The power seat feature operates independent of the ignition position.

The 6-way power seat feature moves the seat in 6 possible directions: the seat can be moved forward or backward and the front and back of the cushion can be moved up and down independently. The power seat feature operates independent of the ignition position.

The power seat motors are hardwired to the seat control switch. The circuits are normally at ground through the seat control switch. An individual circuit is switched to voltage when a specific adjustment position is selected.


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.

NOTE: A memory recall in progress does not prohibit the initiation of another memory recall; the most recently requested memory recall will be executed.

The memory driver seat feature allows the driver to program a personalized seat position that can be recalled using the memory switch or a Remote Keyless Entry (RKE) transmitter (if associated). There are 2 memory settings possible. The power exterior mirrors, power adjustable pedal (if equipped) and power steering column (if equipped) positions are also stored and recalled with the power driver seat positions. The power steering column memory positioning is only used to raise the column upon easy exit and position it back upon easy entry.

The Driver Seat Module (DSM) does not require calibration to the driver seat track, although soft stops must be set within the seat track physical limits.

The driver seat control switch provides voltage to the DSM when activated. The neutral position of each driver seat control switch position is a ground state through the seat control switch contacts. A voltage input causes the DSM to output voltage and ground to the appropriate motor until the input is removed.

As the seat is adjusted, the DSM constantly monitors the motor position sensors to record the current seat position. The DSM will remove voltage from the motor upon termination of the seat control switch input or if the DSM does not see movement from the motor by monitoring the position sensor.

The DSM communicates DTCs and other information using the MS-CAN communication bus. Refer to Information Bus for information concerning MS-CAN bus communication.

This only diagnoses concerns specific to the memory seat. To diagnose an exterior mirror concern, refer to Mirrors. To diagnose a power adjustable pedal concern, refer to Hydraulic System, Brakes &/or Brake Pedal Assy. To diagnose a power steering column concern, refer to Steering Column.

For information on programming memory positions or recalling a stored memory position, refer to Memory Position Programming Programming and Relearning.


Easy Entry/Exit Feature

The easy entry/exit feature is a function of the DSM that moves the driver seat backwards about 51 mm (2 in) and the power steering column (if equipped) to the full upward position when the ignition key is removed from the ignition switch. The DSM receives a key out command over the MS-CAN and operates the driver seat rearward and the steering column upward. The DSM will cancel this operation if a valid input command is received from the driver seat control switch, memory SET switch, adjustable pedal control switch, exterior mirror control switch, power steering column switch or if the function has been disabled.

The DSM will record the current seat and power steering column (if equipped) positions before operating the seat and column for an easy exit operation. This recorded position will be used to return the seat and steering column to this position on the easy entry operation. During easy entry operation, the seat and steering column are returned to the position previous to the easy exit operation. Easy entry operation will be cancelled if a valid input command is received by the DSM.

The easy entry/exit feature can be enabled/disabled using a scan tool. When enabled, the feature becomes a user accessible item on the message center allowing the user to turn the feature on and off. Refer to the Owner's Literature or Instrument Panel, Gauges and Warning Indicators for information on the message center.


Remote Keyless Entry (RKE) Transmitter

NOTE: A memory recall in progress does not prohibit the initiation of another memory recall; the most recently requested memory recall will be executed.

A Remote Keyless Entry (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 if it has been associated with a memory position. The second depression of the unlock switch, which unlocks passenger doors, does not initiate a memory recall.

For information on diagnosing an RKE concern or associating a RKE transmitter to a memory position, refer to Doors, Hood and Trunk &/or Locks.


Driver Seat Module (DSM) Hard Stop/Soft Stop

A hard stop occurs when one of the memory seat track, seat backrest recliner or power steering column axes physically reach the end of travel and can go no further. A soft stop occurs when the seat or steering column stops before physically reaching the end of travel. The hard stop is set by seat or steering column design and cannot be changed or adjusted. The soft stops are set by the DSM to prevent unnecessary stress on the seat, steering column and motors. The seat track axes are forward/rearward, front up/down and rear up/down. The seat backrest axis is forward/rearward and the steering column axis is up/down. The DSM will use a preset distance from the hard stop to determine where the soft stop will occur. When an axis reaches the hard stop and the switch is held for approximately one second, it will then back up 180 milliseconds and establish the soft stop for that end of travel. The DSM uses this "back up" strategy to check sensor integrity any time movement has stopped prematurely due to a sensor failure or obstruction. After a new seat track, seat recliner motor, power steering column or DSM is installed, allow the DSM to reset the soft stops by operating the component(s) in all directions through the full range of travel. This will prevent premature stopping points when the component(s) are initially operated after service is complete.


Heated Seats - Front

The heated seat system operates independently from the climate control system and is controlled by the heated seat module located underneath the front passenger seat cushion. The heated seat buttons are part of the Front Controls Interface Module (FCIM) controls. When a heated seat button on the FCIM is pressed, a request message is delivered via Controller Area Network (CAN) communication to the HVAC module. The HVAC module then provides a momentary ground to the heated seat module to command the system on or off.

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 communication bus circuits. 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 HVAC module monitors the control circuits to the heated seat module and will set a DTC if a circuit fault is detected. Refer to the HVAC Module DTC Chart. HVAC Module DTC Chart

The heated seat module is designed with an auto-configuration feature for use with heated seat systems equipped with dual contact switches. This feature enables additional input circuits intended for rear heated seats, if equipped, and will cause the front 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


Heated Seats - Rear, Crew Cab

Rear heated seats are controlled by the heated seat module located behind the rear 60 percent seat backrest and a dual contact switch attached to each rear door panel. When the heated seat switch is pressed, a momentary ground signal is sent to the heated seat module. The heated seat module then supplies voltage to the heater circuit. The seat cushion and backrest heater mats are wired in series and supplied voltage by the same output. The heated seat module monitors inputs from a temperature sensor, located in each cushion heater mat and maintains seat temperature by cycling output voltage to the heater grids as necessary to maintain the set point temperature. The heated seat module supplies voltage to the appropriate indicator circuit in the heated seat switch. The heated seat module does not time out and will remain on until switched off or ignition is OFF.

The heated seat module does not report DTCs and does not communicate on any network. If a fault is detected, the affected seat system will be disabled. The faults detected will be:

- a heater feed circuit short to battery, ground or open.
- sensor circuit short to battery or open.
- heated seat switch stuck closed to ground.
- heated seat switch low and high inputs shorted together.

To reset the module, cycle the ignition OFF and then ON. After the heated seat module has been reset, the module will return to an off state.

A new heated seat module must be configured after installation for correct operation. Heated seat module configuration occurs automatically when the low heat mode button is pressed on either rear heated seat switch. Until the module is correctly configured, the heated seats will operate incorrectly from the high heat mode button on either heated seat switch by following a sequence of high, low and off with each button press. After the low heat mode button is pressed on either heated seat switch, the module will correctly configure and the system will operate correctly.


Climate Controlled Seat System

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

NOTE: When installing a new Dual Climate Controlled Seat Module (DCSM), it is necessary to carry out Programmable Module Installation (PMI). Refer to Information Bus. Programming and Relearning

Both the driver and front passenger climate controlled seats are independently controlled electronically by the DCSM mounted to the bottom of the passenger seat cushion. The climate controlled seat system only operates with the engine running, however, if using a scan tool to command the DCSM, diagnostic testing can be carried out with the ignition ON engine OFF in 15 second durations. The system receives voltage from Battery Junction Box (BJB) fuse 69 (30A) supplying battery voltage into the DCSM.

If one of the voltage supply circuits opens, both seats will remain operational because the circuits are connected internally in the DCSM.

If a fault occurs setting a DTC specific to either climate controlled seat, only the affected seat will be disabled by the module. If the system shuts down due to a DTC fault, cycling the ignition to OFF and then ON again will reset the DCSM to function until the DTC resets.

The 4 climate controlled seat switches (identified with seat icons) on the HVAC module activate each seat system setting and illuminate indicators above each switch to indicate the operating mode. Each switch uses 3 indicators for HIGH, 2 indicators for MED and 1 indicator for LOW.

Each driver and front passenger seat cushion and backrest is equipped with a Thermo-Electric Device (TED) and blower motor assembly. 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 where it is distributed along the surface of the cushion and backrest of the seat. Once activated, the DCSM maintains the heating/cooling modes until deactivated.

The temperature differences between the individual heated and cooled settings is minimal. For example, it is difficult to distinguish between LOW cool and MED cool settings. Measuring seat temperature at different settings is possible by monitoring the DCSM PIDs using the scan tool.

The HVAC module communicates climate controlled seat commands to the DCSM using the Medium Speed Controller Area Network (MS-CAN) bus. The MS-CAN bus is connected to the Data Link Connector (DLC) for diagnostic use. No direct connection exists between the DCSM and HVAC module for the climate controlled seat switches. The climate controlled seats can be commanded on or off using the scan tool to verify both module communication on the MS-CAN bus and operation of the DCSM. This method may be useful for isolating a control switch concern. Refer to Information Bus for additional information concerning CAN bus communication.

Heating Characteristics

- In heat mode, the TED circuits of a given seat are wired in parallel internally in the DCSM.
- The climate controlled seat system draws approximately 24 amperes, with both seats heating, until reaching the set point and then the system operates at a reduced amperage to maintain the climate setting.
- In heat mode, the TED can add up to 40°C-60°C (72°F-108°F) to the ambient inlet air temperature as it passes over the TED.
- The system control settings are based on the 3 indicators above each climate controlled seat heat switch button on the HVAC module.
- In the LOW setting, the DCSM is set to maintain TED temperature at approximately 46°C (115°F).
- In the HIGH setting, the DCSM is set to maintain TED temperature at 65°C (149°F).
- When heating, the DCSM will vary the speed of the blowers and the TED duty cycle in order to reach and maintain the temperature determined by the switch setting (closed loop operation). Refer to the following table for heating mode temperatures.





Cooling Characteristics

- In cool mode, the TED circuits of a given seat are wired in series internally in the DCSM.
- The climate controlled seat system draws approximately 7 amps.
- In cool mode, the TED can remove up to 8°C (14°F) from the ambient air temperature entering the system.
- The system control settings are based on the 3 indicators above each climate controlled seat cool switch button on the HVAC module. The first setting is HIGH (3 indicators), the second setting is MED (2 indicators) and the third is LOW (1 indicator) then OFF (no indicators).
- When cooling, the DCSM maintains constant speed of the blowers and constant TED supply voltage (duty cycle) in open loop COOL mode (refer to the following table).





The climate controlled seat system is deactivated by one of the following actions:

- Selecting the HVAC module setting to manual OFF
- Turning the vehicle OFF

If the temperature at one of the TEDs falls below 5°C (41°F), the DCSM will shut down the TEDs and initiate system recovery mode. If the temperature continues to drop below 2°C (36°F), the DCSM will shut down the blowers in the affected seat.

Climate Controlled Seat System Recovery Mode

NOTE: The presence of overtemperature faults (DTCs B2729, B2730, B272A and B272B) can be induced by incorrect operation of the climate controlled seat system after an initial heat setting has been attained. If a heat setting is repeatedly turned OFF and ON in an attempt to increase the seat temperature or repeatedly toggled between heat and cool modes, an overtemperature condition can result and the DTCs will be set.

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 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 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. This 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 will disable that seat (fault mode) and remain off until the ignition is cycled. Also, if the DCSM detects temperature differential fault twice during the same ignition cycle, it will shutdown. When a fault causes a shutdown, the climate controlled seat indicators will turn off and that seat will not be operational until the next key cycle.