Seats: Description and Operation
INTRODUCTIONPower Seat
Power seats can be adjusted in eight directions; up, down, forward, back, tilt forward, or tilt rearward. Four reversible motors and a transmission located on the seat tracks provide the various seat movements. The electrical circuit is protected by a 40 amp fuse in the Power Distribution Center (PDC) and a 30 amp circuit breaker located in the wire harness under the driver's seat.
Memory Seat and Mirrors System
Memory Seat and Mirrors system is available only on Town and Country (Luxury Class) vehicles.
The Memory Seat/Mirror Module (MSM Module) is mounted under the driver's seat, on the inboard upper track with Torx head screws. The MSM Module provides the driver with an adjustable seat, recliner, and power side view mirror positioning controller that remembers stored positions and will recall those positions on command.
The Memory Seat/Mirror Module reads all seat and recliner switch inputs and operates the seat and recliner motors in response to switch actuation. The MSM Module monitors position sensing potentiometers (mounted on the motors) for seat and recliner positioning.
The MSM Module operates the power side view mirror motors through solid state drivers (electronic switches) in the recall mode only, and follows the glass face position by means of rheostats built into the motor pack assembly of the mirrors. Normal electrical operation of the mirrors is accomplished by actuation of the power mirror switch.
The Memory Seat/Mirror Module monitors the memory switches and has the capability to store desired positions in non-volatile memory in response to a valid input sequence. Refer to Memory Selector Switches (1, 2, and S) and Remote Keyless Entry (RKE) Data Link. The memory seat/mirror module also can activate the previously described motors in response to a recall request from an individual memory switch.
The Memory Seat/Mirror Module monitors a data link between the RKE receiver and the Body Control Module (BCM) and will respond to stored information or modify stored information when requested by a valid data stream.
The Memory Seat/Mirror Module is connected to the system through a seat wiring harness that interfaces will all of the components within the seat structure, and with electrical distribution wiring harness connections to the non-seat mounted components. The module operates the seat and recliner motors through relays: four dedicated to track forward/rear- ward, track front up/down, track rear up/down, and recliner forward/rearward. A fifth relay controls the direction of operation of those motors.
SYSTEM OPERATION
Power Side View Mirror Position Sensing
The mirror switch on the instrument panel operates the outside rear view mirrors independently of the memory seat/mirror module. The module activates the mirror motors only when in its recall mode.
The side view mirrors have position sensing rheostats built into each side view mirror vertical and horizontal motor assembly. These rheostats provide a sense voltage to the memory seat/mirror module that indicates where the mirror is moving to or where its position is at when the module is activated but the mirror motor is not moving.
Memory Selector Switches
The memory selector switches are mounted on the driver's door trim panel within easy reach of the driver. They provide a means to set or recall either of two positions of seat and recliner, and the side view mirrors as chosen by the driver.
The inputs from these switches to the memory seat/mirror module is a ground level signal.
1. Adjust the seat, recliner and side view mirrors to the desired position.
2. Press momentarily and release memory switch S.
3. Press momentarily and release memory switch 1 or 2. Do NOT press any switches for 10 seconds.
4. To program the second driver's position, follow the above sequence.
5. To recall either of the programmed positions momentarily press and release either memory selector switch 1 or 2.
Definition Of: Momentarily And Release
The memory seat/mirror module has switch input timing requirements of a minimum press momentarily time of 250 milliseconds followed by a maximum hold time of 5 seconds, followed by a maximum release time between steps of 5 seconds that must be met for proper operation of the system.
Seat and Recliner Switches
The seat and recliner switch assembly is mounted outboard on the seat side-shield. Press and hold the desired seat or recliner switch to effect movement. The Memory Seat/Mirror Module (MSM Module) will drive a maximum of 2 motors at a time in a given direction. If conflicting directions are requested, the priority for response will be as follows:
- Seat Track Rearward
- Seat Front Down
- Seat Rear Down
- Recliner Rearward
- Seat Track Forward
- Seat Front Up
- Seat Rear Up
- Recliner Forward
The inputs from these switches to the MSM Module is a current limited battery source fed by the MSM Module. This protects the MSM Module printed circuit board traces from acting as fuses. All of these switch contact inputs to the module are normally closed to ground, except when actuated.
Position Sensing Seat and Recliner Potentiometers
A potentiometer is mounted to each seat track and recliner motor end-bell to provide a sense voltage to the Memory Seat/Mirror Module that will indicate to the module where the seat track or recliner is positioned.
This sense voltage is derived from a 5 Volt source provided by the module to the potentiometer. The sense voltage is input into the module and stored by the Memory Seat/Mirror Module.
CIRCUIT OPERATION
Power to both driver and passenger seats, as well as power door locks, rear blower, and front fog lamps (if so equipped), is provided by the A3 circuit through a 40 amp MAXI-fuse in the Power Distribution Center (PDC) under the hood. If all of these devices are nonfunctional, replace the MAXI-fuse. If the new MAXI-fuse blows immediately, correct the wiring short to Ground that could be on any of those aforementioned loads before proceeding further.
Once the power is back ON, if the power seats still do not work, check the 30 amp circuit breaker that is located in the driver's seat wiring harness approximately 10 inches from the 4-way connector. The power feed circuit to the 30 amp circuit breaker is 14 ga. A3 RD/WT.
Following the 30 amp circuit breaker is a 14 ga. wire designated as F35 RD that provides power into the Memory Seat/Mirror Module and is double crimped with a 14 ga. F35A RD that provides power to the passenger seat through the 4-way connector.
If the power door locks, rear blower, and front fog lamps (if so equipped) are functional and the seats are both nonfunctional, repair/replace the open wiring and/or circuit breaker in the driver's seat harness to correct the condition.
Ensure that the 12 ga. ground wire Z1 BK from the electrical distribution wiring ground splice into the 4-way connector is providing ground. The Z1 BK is double crimped at the seat harness side of the 4-way connector taking a 14 ga. Z1 BK into the 10-way connector (cavity 7) 14 ga. This double crimp carries a 20 ga. Z1A BK to cavity 3 of the power seat switch 10-way If the passenger power seat is functional, and the driver's seat is nonfunctional examine the circuit F35 RD from the double crimped circuit breaker connector into the 10-way connector cavity 8 of the control module for continuity. Repair or replace as necessary. If the driver's seat is still nonfunctional, use a multi-function meter to check the P9 RD 20 ga. circuit from the control module 21-way connector (cavity 11) to the power seat switch 10-way connector (cavity 5) This is a low current battery feed from the control module that will not illuminate a test lamp.
During shipping of the vehicle, an M1 circuit 10 amp fuse (labeled IOD) is temporarily removed from the PDC in the engine compartment to eliminate unnecessary battery depletion. However, this fused circuit being open (that feeds through the electrical distribution wiring to cavity 16 of the 25-way connector) will not stop manual seat actuations from taking place (only recall mode requests) during shipping.
1. If the memory seat/mirror module does not respond with a relay click to any seat switch input (as well as the desired motion) when actuated, proceed with the following analysis:
- Verify power ON F35 and ground Z1 into the system as indicated above.
- Verify all connectors are mated with the memory seat/mirror module.
- Place the vehicle gear shift lever in any position except PARK (causes the Memory Seat/Mirror Module to wake-up and provide a position sense voltage to the seat motor potentiometers and the mirror rheostat(s). This voltage can be checked at the appropriate cavities of the 21 and 25-way connectors.
- Verify the switch connector is mated with the seat switch on the inside of the outboard side-shield.
- Verify battery voltage at the P9 circuit referenced to the Z1A ground reference (cavity 1) of the seat switch. If P9 low current battery is not available coming from the module, replace the Memory Seat/ Mirror Module.
- If P9 low current battery is present at (cavity 5) referenced to ground Z1 (cavity 1) of the seat switch, verify the presence of the P9 voltage at the switch outputs. If there is no output voltage from the switch, replace the switch.
- If P9 voltage is present at the output of the switch, but there is no reaction from the memory seat/mirror module, verify that the P9 voltage is present at the appropriate 21-way connector pins into the module. If the P9 voltage is not present at the 21-way connector, repair or replace the seat wiring harness. If the verification check of the seat wiring harness is correct, replace the control module.
2. If the control module does not respond with a relay click to a specific seat switch when actuated, verify the continuity of the particular circuit between the seat switch and the Memory Seat/Mirror Module. If the P9 voltage is present at the correct input of the 21-way connector of the module when the switch is actuated, but there is no response by the module, replace the Memory Seat/Mirror Module.
3. If the Memory Seat/Mirror Module responds with a relay click when a seat switch is actuated for a given direction, but there is no reaction from a seat or recliner motor relating to that switch input, disconnect the 10-way connector from the control module. Jumper the battery and ground from cavities 8 and 7 of the seat harness 10-way connector to the proper cavities for the seat or recliner motor in question and direction of travel desired. If the motor operates, replace the control module. If the motor does not operate, verify continuity of the wiring into the motor 2-way connector. Repair or replace the wiring as necessary If the wiring has continuity, and the motor will not operate when fed directly, replace the track assembly, since the motor/transmission combinations are not designed to be serviced on an individual basis.