+15 Power Supply Circuit

Fault symptom
The alarm is not set off when the ignition is switched on and the alarm is armed.







Diagnostic procedure
1 Check fuse 17
- Check that fuse 17 is intact and live.
- Connect the test lamp to the fuse and a good grounding point.
With the ignition switch in the "ON" (+15) position, the test lamp should light up.
Does it light up?
[YES] Continue with point 2.
[NO] Continue fault diagnosis as described in Service Manual 3:2 "Electrical system, +15 power supply".

2 Check the electronic control module's power supply (+15 circuit)
- Unplug connector H33-3.
- Connect the test lamp to pin 25 of connector H33-3 and a good grounding point.
- Turn the ignition switch to the "ON" (+15) position.
The test lamp should light up.
Does it light up?
[YES] Continue with point 3.
[NO] Proceed to point 6.






3 Check the engine management system's power supply (+15 circuit)
- Connect a jumper lead between pins 25 and 18 of connector H3373.
- Turn the ignition switch to the "ON" (+15) position.
The "CHECK ENGINE" lamp (MIL) in the main instrument display panel should light up.
Does the lamp light up?
[YES] Proceed to point 7.
[NO] Continue with point 4.

4 Check the wiring between connectors H33-3 and H33-4.
Check the wiring harness for continuity between pin 18 of connector H33-3 and pin 21 of connector H33-4.
The resistance should be < 1 ohm.
Is the resistance OK?
[YES] Continue with point 5.
[NO] Repair or replace the wiring harness.







5 Check the wiring connected to the engine management system
Check the wiring harness for continuity between pin 21 of connector H33-4 and
- Pin 60 of the Trionic electronic control module
- Pin 27 of the Motronic 2.10.3 electronic control module
- Pin 27 of the Motronic 2.8.1 electronic control module depending on the engine version.
The resistance should be < 1 ohm.
Is the resistance OK?
[YES] Continue fault diagnosis as described in "Engine management system TRIONIC" or "MOTRONIC".
[NO] Repair or replace the wiring harness.

6 Check the wiring connected to fuse 17
- Connect the test lamp to fuse 17 and a good grounding point.
- Turn the ignition switch to the "ON" (+15) position.
The test lamp should light up.
Does it light up?
[YES] Check and repair or replace the wiring.
[NO] Continue fault diagnosis in +15 power supply". Electrical Diagrams







7 Check the wiring connected to the electronic control module
- unplug the electronic control module.
- Check the wiring harness for continuity between:
- connector H33-3 (pin 25) and the electronic control module (pin 10)
- connector H33-3 (pin 18) and the electronic control module (pin 22)
The resistance should be < 1 ohm.
Is the resistance OK?
[YES] Continue with point 8.
[NO] Repair or replace the wiring harness.

8 Final test
Start the car and check to see if the fault symptom persists.
Does the trouble persist?
[YES] Continue as described in "Before Changing The Electronic Control Module".
[NO] The remedial measures taken were correct or the fault is of intermittent nature.