EXH Lamp Permanently On

EXH Lamp Permanently On

Fault symptoms
EXH lamp permanently on

Diagnostic help
Check the temperature sensor circuit.
Check the relay, EXH warning (416), on the dashboard's main relay board.

Check the wiring
Jiggle the wiring harness at several points and in different directions to reveal intermittent breaks and short-circuits in the wiring harness. Observe the multimeter, test lamp or diagnostic instrument while doing this.





Diagnostic procedure

1. Check the fault symptoms
- Turn the ignition switch to the ON position.

In what way is the EXH lamp faulty?
THE EXH LAMP DOES NOT LIGHT UP
- Go to point 2.
THE EXH LAMP IS PERMANENTLY ON
- Go to point 6.





2. Check the EXH lamp's power supply.
- Remove component: EXH relay.





- Connect a jumper lead between terminals 2 and 4 on the relay holder.





- Turn the ignition switch to the ON position.





- The lamp should light.

Test results OK?
YES
- Go to point 3.
NO
- Repair or replace the wiring.
- Go to point 9





3. Check the EXH relay's ground connection
- Connect a test lamp to pins 4 and 5 of the relay holder.





- The test lamp should light.

Test results OK?
YES
- Go to point 4.
NO
- Repair or replace the wiring.
- Go to point 9.





4. Check the wiring and operation of the main instrument unit.
- Connect a test lamp to terminal 2 of the relay holder and a good grounding point.





- The EXH lamp in the main instrument unit should light.

Test results OK?
YES
- Change EXH relay.
- Go to point 9.
NO
- Go to point 5.





5. Locate the fault
- Unplug the main instrument unit's 20-pin connector: (540)





- Connect a test lamp to pin 4 of the female connector and a grounding point.





- The test lamp should light.

Test results OK?
YES
- Continue fault diagnosis by fault symptom in Group 3, Electrical System, "Main instrument unit": EXH.
- Go to point 9.
NO
- Repair or replace the wiring harness between terminal 2 of relay holder 416 and pin 4 of female connector 540.
- Go to point 9.





6. Check the lead connected to the main instrument unit.
- Turn the ignition switch to the ON position.





- Remove component: EXH relay.





- The EXH lamp should go out.

Test results OK?
YES
- Go to point 7.
NO
- Repair or replace the lead between terminal 2 of the relay holder and the EXH lamp in the main instrument unit.
- Go to point 9.





7. Check the wiring harness between the relay and the sensor.
- Check the wiring harness between the EXH relay and the EXH sensor for shorting or an open circuit.

Is the lead OK?
YES
- Change: EXH relay.
- Go to point 8.
NO
- Repair or replace the lead/Change the wiring harness.
- Go to point 9.





8. Function test
- Clear the diagnostic trouble codes in all systems.
- Carry out a function test.

Test results OK?
YES
- The steps taken to rectify the fault were correct.
NO
- Change: EXH temperature sensor
- Go to point 9.





9. Final check
- Clear the diagnostic trouble codes in all systems.
- Carry out a function test.

Test results OK?
YES
- The steps taken to rectify the fault were correct.
NO
The cause of the fault is probably to be found in:
- the EXH relay
- the EXH temperature sensor
- the wiring harness.