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 reclining motor), a pulse signal returns to power seat ECU. Power seat ECU uses pulse signals to determine position of seat in relation to memorized position. If 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 power seat ECU. Remove power seat ECU, but leave wiring harness connectors attached.
- Connect a jumper wire between chassis ground and power seat ECU connector "A", terminal No. 11. See Figure. This puts the power seat ECU into a check mode (diagnostic mode).
- Connect an analog (needle-type) voltmeter between chassis ground and terminal No. 3 of power seat ECU connector "A". A "ready" code should be output by power seat ECU (needle deflects once every second).
- While watching voltmeter, use manual seat switch to operate each seat motor (on vehicles with lumbar support, do not operate lumbar motor because system does not monitor its position).
- While motor is running and seat is moving, voltmeter needle should deflect every .25 second (okay indication). If system is okay is indicated, return to TROUBLE SHOOTING . If voltmeter needle deflects every .50 second (no good indication) go to next step.
- If voltmeter indicates a "no good" code for any motor while it is running, disconnect wiring harness connectors from position sensor and motor. Using jumper wires, connect battery and voltmeter to suspect position sensor and related motor. See Fig 1 and Fig 2 .
- While motor is running, voltage should be about half of battery voltage. While motor is stopped, voltage should be zero or battery voltage, 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 power seat ECU. See WIRING DIAGRAMS . If circuit is okay, replace power seat ECU.