Control Module Power Supply, Checking

Control Module Power Supply, Checking

Requirements
- Fuses for engine electronics OK
- Battery voltage at least 12.7 V
- Alternator OK

Work sequence
- Connect test box V.A.G 1598/31 at wiring harness to engine control module. Actual engine control module is not to be connected. Wiring And Component Check Using Test Box V.A.G 1598/31
- Switch on ignition.

NOTE:
- Engine control module is supplied with positive voltage via contact 21 (terminal 15), contact 62 (terminal 30) and contact 3 (from main relay).
- Ground supply for the engine control module is provided by way of contacts 1 and 2.
- Connect multimeter for voltage measurement as follows.

Test box V.A.G 1598/31 Measure to
Socket
1 Battery positive
2 Battery positive
62 Engine Ground

- Specification: approx. battery voltage.

- Connect multimeter for voltage measurement as follows.

Test box V.A.G 1598/31 Measure to
Socket
3 Engine Ground
21 Engine Ground

- Switch on ignition.
Specification: approx. battery voltage

If readings do not match specifications:
- Check wiring.
- Check Motronic ECM power supply relay -J271-.