Position Sensor Circuit Test
NOTE:
Power seat ECU applies an 8-volt reference signal to each position sensor. When a power seat motor turns one revolution (20 revolutions for the reclining motor), a pulse signal returns to driver's power seat ECU. Power seat ECU uses pulse signals to determine the position of seat in relation to memorized position. If driver's power seat ECU does not receive a signal, it prevents seat from returning to memorized position, even if seat motor is okay.
- At driver's seat, remove bolts for front vertical adjuster. Lift front end of seat cushion slightly for access to driver's power seat ECU (do not lift too far; harness clamp may come loose). Remove driver's power seat ECU, but leave electrical connectors attached.
- Connect a jumper wire between chassis ground and the following terminal of driver's power seat ECU connector. This puts the driver's power seat ECU into a check mode (diagnostic mode).
- See Figure.
- Connect an analog (needle-type) voltmeter between chassis ground and terminal No. 17 of driver's power seat ECU connector "B". Voltmeter should indicate a "ready" code (needle deflects every second).
- While watching voltmeter, use the seat switch to operate each seat motor (on vehicles with lumbar support, do not operate lumbar motor because the system does not monitor its position).
- While motor is running (seat moving), voltmeter should indicate an "okay" code (needle deflects every .25 second). When motor stops running (seat stops moving in either direction), voltmeter should indicate a "no good" code (needle deflects every .50 second).
- If voltmeter indicates an "okay" code for each motor, go to next item listed under TROUBLE SHOOTING. If voltmeter indicates a "no good" code for any motor while it is running, disconnect electrical connectors from position sensor and motor.
- Connect 12 volts across terminals No. 3 (positive lead) and No. 2 (negative lead) of position sensor connector. See Fig 1. Connect voltmeter between ground and terminal No. 1 of position sensor connector. While watching voltmeter, connect 12 volts across motor connector terminals.
- While motor is running, voltage should be about half of battery voltage. While motor is stopped, voltage should be 0-12 volts, depending on where the seat is stopped within its range of travel.
- If voltage is not as specified, replace position sensor. If voltage is okay, check for faulty circuit between position sensor and driver's power seat ECU. If circuit is okay, replace driver's power seat ECU.