Principles of Operation

PRINCIPLES OF OPERATION

Driver and Passenger Power Seats Without Memory
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 switch 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.

Power Driver Seat With Memory

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

This vehicle uses 2 different driver seat modules (DSMs) and will be referred to as early production and late production. The circuit locations at the connectors are different and the DSMs are not interchangeable. Before diagnosing or servicing, make sure the correct DSM has been identified. Refer to Vehicle/Diagrams, Memory Seats for schematic and connector information.

The driver power memory seat is controlled by the 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 and adjustable pedal positions are also stored and recalled with the driver memory seat positions.

For information on programming memory positions or recalling a stored memory position, refer to Memory Position Programming. For information on remote keyless entry transmitter programming or to diagnose a concern, refer to Locks. Programming and Relearning

The DSM is located underneath the driver seat. Programmable module installation (PMI) must be carried out when installing a new DSM. Refer to Information Bus (Module Communications Network). The DSM does not require calibration to the driver seat track, although soft stops must be set within the seat track physical limits. Refer to Driver Seat Module (DSM) Hard Stop/Soft Stop in Principles of Operation.

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 has the ability for soft stops both at the upper and lower limits on all axis of the driver seat. When an axis reaches the hard stop and the switch is held for approximately one second it will then back up 180 ms and establish the soft stop for that axis in that direction. The DSM uses this `back up' strategy to check sensor integrity any time movement has stopped prematurely due to a sensor failure or obstruction.

The DSM communicates DTCs and other information using the medium-speed controller area network (MS-CAN) communication bus. It should be noted for diagnostics 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 (Module Communications Network) for information concerning MS-CAN bus communication.

This section only diagnoses concerns specific to the memory seat. To diagnose a memory exterior mirror concern, refer to Mirrors. To diagnose a memory adjustable pedal concern, refer to Brakes and Traction Control.

Remote Keyless Entry (RKE) Transmitter
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 a RKE concern or associating a RKE transmitter to a memory position, refer to Locks.

Driver Seat Module (DSM) Hard Stop/Soft Stop
A hard stop occurs when one of the memory seat track axes physically reach the end of travel and can go no further. A soft stop occurs when the seat stops before physically reaching the end of travel. The hard stop is set by seat design and cannot be changed or adjusted. The soft stop is set by the driver seat module (DSM). The seat track axes are forward/rearward, front up/down and rear up/down. To prevent unnecessary stress on the seat and motors, the DSM will set soft stop positions, 2 for each moving axis. 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 in the same direction, the DSM establishes the soft stop for that axis in that direction.

Setting the Soft Stop

NOTE: If a new DSM or driver seat track has been installed, all driver seat track soft stops must be reset.

Use the following procedure once a new seat track or DSM has been installed.

During the setting procedure, if the seat track stops before the end of travel has been reached, the DSM has stopped at a previously set soft stop. To set the new soft stop, release the seat control switch and press again in the same direction until the seat track stops at the hard stop for that given direction.
1. Turn the ignition key to the ON position.
2. Press the seat control switch horizontal button forward until the seat track stops.
3. Keep the horizontal button pressed forward for one second after the seat track reaches its forward end of travel. The horizontal forward soft stop has been set, release the switch button.
4. Repeat steps 2 and 3 for all seat track axes in both directions.

Heated Seats
The driver and passenger heated seats share a common ignition feed via the heated seat relay. The heated seat relay is energized when the ignition is ON. A shared ground source supplies the heated seat control switches and the heated seat elements. The heated seat control switches are latching-type switches; continuity through the switch will remain, regardless if voltage is supplied to the switch or not, until the switch is pressed to place it in the OFF setting. When the heated seat control switch is pressed with the ignition switch in RUN or START, voltage is supplied to the bi-metallic thermostat that is part of the seat cushion element. The seat cushion element and seat backrest element are wired in series and supplied voltage by the same output of the bi-metallic thermostat that is part of the seat cushion element. The cushion element and seat backrest element are wired in series and supplied voltage by the same output. The heated seat will remain on until the heated seat control switch is pressed and voltage is no longer supplied to the bi-metallic thermostat. If the ignition source is removed from the heated seat, the heated seat system will return to ON with the ignition switch in the RUN state until the switch is pressed. The heated seat system is designed to maintain the temperature by the opening (no voltage to the heated seat elements) and closing (voltage supplied to the heated seat elements) of the bi-metallic thermostat.