Principles of Operation

Seats

Principles of Operation

Driver and Passenger Power Seats Without Memory

The 10-way power 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 8-way power seat control feature moves the seat in 8 possible directions. It is like the 10-way power seat, less power lumbar.

The 6-way power seat control feature moves the seat in 6 possible directions. It is like the 10-way power seat, less power lumbar and recline.

The power seat motors are hard-wired 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.


Power Driver 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 driver power memory seat is controlled by the Driver Seat Module (DSM). The memory 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. There are 2 memory settings possible. The exterior mirror positions are also stored and recalled with the driver memory seat positions.

The driver seat control switch provides voltage to the DSM when activated. The NEUTRAL position of the driver seat control switch position is a ground state through the seat control switch contacts. A voltage input causes the DSM to power the appropriate motor until the input is removed. Ground is the normal state of the motor circuits through the DSM and is not switched to control the motors. The DSM internally switches the appropriate circuit from ground to voltage for operating the motors.

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. It should be noted for diagnostics that because Controller Area Network (CAN) bus communication is more robust and reliable than other methods, it may be possible to have limited module communication with one of the CAN bus circuits disconnected or shorted to ground. Refer to Information Bus for information concerning MS-CAN bus communication.

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

The DSM is located under the driver seat. To install a new DSM, refer to Body Control Systems. Programmable Module Installation (PMI) must be carried out when installing a new DSM. Refer to Information Bus.

This section only diagnoses concerns specific to the memory seat. To diagnose a memory exterior mirror concern, refer to Mirrors.


Easy Exit/Easy Entry

The easy entry/exit feature is a function of the DSM that moves the driver seat backwards about 2 in (50.8 mm) when the ignition key is removed from the ignition. The DSM receives a key out command over the MS-CAN communication network and powers the driver seat rearward. This function will not operate if the seat is less than the 51 mm (2 in) travel distance to the end of the track or the function has been disabled. The DSM will also cancel this operation if a valid input command is received from the driver seat control switch, memory SET switch or exterior mirror control switch.

The DSM will record the current seat position before powering the seat for an easy exit function. This recorded position will be used to return the seat to this position on the easy entry operation. During easy entry operation, the seat is returned to the position previous to the easy exit operation. Easy entry operation will be cancelled if a valid input command from the seat control switch, memory SET switch or exterior mirror control switch 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.


Heated Seats

The heated seat system is controlled by the heated seat module located underneath the front passenger seat cushion. The heated seat switches are part of the HVAC module but the heated seat system operates independently from the climate control system. The heated seat module supplies voltage to heater mats located in the seat cushion and backrest to heat the seat. The heated seat module regulates seat temperature by monitoring resistance of a thermistor type thermostat located in the cushion heater mat. 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 will 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 on other vehicles equipped with dual contact 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


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.

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 Key ON Engine OFF (KOEO). The system receives voltage from Battery Junction Box (BJB) fuse 12 (30A) supplying battery voltage on circuit SBB12 (GN/RD) into DCSM C3305a pin F. The system also receives voltage from BJB fuse 11 (30A) supplying battery voltage on circuit SBB11 (BU/RD) into DCSM C3305a pin E.

If only one of the BJB fuses 11 or 12 open, both seats will remain operational because the voltage supply circuits are internally connected in the DCSM.

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

The 4 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, 3 indicators for HIGH, 2 indicators for MED 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.

Each driver and front passenger seat cushion and backrest is equipped with a 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 MEDIUM 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 MS-CAN communication 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 using the diagnostic 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. It should also be noted that because CAN bus communication is more robust and reliable than other methods, it may be possible to have limited module communication with one of the CAN bus circuits disconnected or shorted to ground. Refer to Information Bus for additional information concerning CAN bus communication.

Heating Characteristics

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, an overtemperature condition can result and the DTCs will be set.

- 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 air temperature entering the system.
- There are 3 manual settings based on the indicators above each seat heat switch button on the HVAC module. The first setting is HIGH (3 indicators), the second setting is MED (2 indicators), the third is LOW (1 indicator) then OFF (no indicators).
- 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 fans and the TED duty cycle in order to reach and maintain the temperature determined by the switch setting.
- Seat heating has a maximum operating duration of 15 minutes.





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 when in cool mode on high setting.
- In cool mode, the TED can remove up to 8°C (14°F) from the ambient air temperature entering the system.
- There are 3 manual settings based on the indicators above each 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 fans and constant TED supply voltage (duty cycle) in open loop cool mode.
- Seat cooling has a maximum operating duration of 30 minutes.





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 affected seat operation.

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. 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 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 for the affected seat and that seat will not be operational until the next key cycle.