Main Relay (Computer/Fuel System): Testing and Inspection

Motronic Engine Control Module (ECM) Power Supply Relay -J271-, Testing

Special tools and equipment
- VAG 1526 A
- VAG1594 A
- VAG 1598/31

NOTE: The Motronic engine control module (ECM) power supply relay -J271-supplies voltage to the ignition coils with power output stages and to the engine control module (pin 121).

Test sequence

- Remove engine cover panel -1- -arrows-

- Unplug 4-pin connector -1- from one ignition coil -2-.

- Connect multimeter (voltage measurement range) as follows:

Connector Contact Measure against
1 Engine Ground

- Switch on ignition.
- Specification: approx. battery voltage

If the specification is not attained:
- Switch off ignition.

- Unplug current supply relay -1- (located under cover on left side of bulkhead).

NOTE: To remove protective cover on vehicles with suspension turret stiffener strut, disengage and move down relay carrier on bulkhead. If necessary, also unplug connector on air mass meter.

- Test for open circuits in the following wiring connection according to current flow diagram:

Relay carrier under cover Connectors on ignition
on left side of bulkhead coils
Contact
2 1

- Correct any open circuit as necessary.

If the wiring is OK:
- Test supply voltage for Motronic current supply relay -J271.
- Test activation of Motronic current supply relay -J271.

Checking voltage supply
- Switch off ignition.

- Connect multimeter (voltage measurement range) as follows:

Relay carrier below cover Measure against
on left side of bulkhead
Contact
1 Engine Ground
3 Engine Ground

- Specification: approx. battery voltage

If the specification is not attained:
- Carry out the following tests (marked with dots):

- Check fuse S10 (infuse carrier, plug-in position10).

- Check fuse S134 (110 A) in main fuse box on battery.
- Test for open circuit in wiring from battery + (terminal 30) via fuse S134 and fuse 10 to Motronic current supply relay -J271 (under cover on left side of bulkhead)

Checking activation
- Switch off ignition.

- Connect multimeter (voltage measurement range) as follows:

Relay carrier below cover Measure against
on left side of bulkhead
Contact
5 Battery positive

- Switch on ignition.
- Specification: approx. battery voltage

If the specification is not attained:
- Switch off ignition.
- Connect test box VAG 1598/31 to wiring harness for engine control module. Do not connect to the engine control module itself. Scan Tool Testing and Procedures

- Test for open circuit and short to positive or Ground in the following wiring connections:

Relay carrier below cover Test box VAG 1598/31
on left side of bulkhead Socket
Contact
5 21

- Correct any open/short circuit as necessary.

If no malfunction is found:
- Install a new motronic engine control module (ECM) power supply relay -J271-.