Heated Rear Seat Not Working

Heated Rear Seat Not Working

Fault symptoms
Rear seat heating does not work for one or both pads.

Conditions
A break in the circuit from the relay to the heating pad or a break in the circuit to pin 9 of the control module.

Diagnostic help
The control module output can be activated and the control module input from the switch can be read using the diagnostic tool.

If the indicator lamp lights on activation of the control module output, the fault probably lies between fuse B and pin 9 on TWICE.
If the indicator lamp does not light on activation of the control module output, the fault probably lies in the circuit from relay (511) to the heating pad (64RL/RR).

Check the wiring
Touch the wiring harness at several different points and in different directions to reveal intermittent faults, breaks and short-circuits in the harness. Monitor the multimeter, test lamp or diagnostic instrument during the test.

Diagnostic procedure

1. Activate the heated rear seat
^ Turn the ignition key to the ON position.






^ Press the button for the heated rear seat.






^ The indicator lamp for the heated rear seat should light.






Test results OK?
YES
^ Go to point 2.
NO
^ Go to point 4.

2. Check power supply to heating pad
^ Unplug the connector: heating pad, rear seat, left side: (64RL)






^ Connect test lamp 86 11 857 between the pin 8 of the female connector for the left-hand heating pad and a good grounding point.






^ The test lamp should light.






Test results OK?
YES
^ Go to point 3.
NO
^ Repair or replace the lead between pin 2 (87) of the relay holder and pin 8 of the female connector for the left-hand heating pad.
^ Go to point 8.

3. Check ground lead from heating pads
^ Connect test lamp 86 11 857 between the pins 8 and 9 of the female connector for the left-hand heating pad.






^ The test lamp should light.






Test results OK?
YES
^ Replace the faulty heating pad.
^ Go to point 8.
NO
^ Repair or replace the lead between pin 9 of the female connector for the left-hand heating pad and grounding point G5.
^ Go to point 8.

4. Check control module input
^ Contact TWICE.






^ Read value: Rear seat heating, switch (TWICE).
^ Hold down the button for the heated rear seat.
^ The diagnostic display should show ON.

Test results OK?
YES
^ Go to point 5.
NO
^ Go to point 6.

5. Check the relay power supply
^ Connect test lamp 86 11 857 between pin 1 of the relay (30) and a good grounding point.






^ The test lamp should light.






Test results OK?
YES
^ Replace: relay, heated rear seat.
^ Go to point 8.
NO
^ Repair or replace the lead between pin 1 of the relay holder and fuse 10 in the dashboard fuse box.
^ Go to point 8.

6. Check switch power supply
^ Connect a test lamp between pin 3 and a good grounding point.






^ The test lamp should light.






Test results OK?
YES
^ Go to point 7.
NO
^ Repair or replace the lead between the fuse B in the dashboard fuse box and pin 3 of the rear seat heating switch.
^ Go to point 8.

7. Check switch
^ Connect a jumper lead between pins 3 and 2 of the female connector.






^ Read value: Rear seat heating, switch (TWICE).
^ The diagnostic display should show ON.

Test results OK?
YES
^ Replace: switch, heated rear seat
^ Go to point 8.
NO
^ Repair or replace the lead between pin 2 of the heated rear seat switch and pin 9 of the TWICE control module female connector.
^ Go to point 8.

8. Final check
^ Delete the diagnostic trouble codes in all systems.






^ Carry out a function check.

Test results OK?
YES
^ The steps taken to rectify the fault were correct.
NO
^ See "Before changing a control module."