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

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







Special tools and equipment
- VAG1526A or Fluke 83 Multimeter
- VAG1594A Connector test kit
- VAG1598/31 Test box

NOTE: The Motronic Engine Control Module (ECM) power supply relay -J271- supplies voltage to the ignition coils with power output stages and the Motronic ECM at pin 121.

Work sequence







- Remove engine cover (arrows).







- Disconnect 4-pin harness connector -1- at one ignition coil -2-.







- Connect multimeter for voltage measurement as follows.

Harness connector Terminal Measure to
1 Engine Ground (GND)

- Switch ignition on.
- Specified value: approx. battery voltage

If specified value is not obtained:
- Switch ignition off.







- Disconnect power supply relay (arrow) below left cover at bulkhead.

NOTE: To remove the protective hood for vehicles with a dome brace, disengage the relay carrier at the bulkhead and swing it downward. Disconnect additional harness connectors at the Mass Air Flow (MAF) sensor, if necessary.







- Check following connection for open circuit according to wiring diagram:

Relay carrier below left cover, Harness connector at
at bulkhead Terminal ignition coils Terminal
2 1

- Repair open circuit in wiring if necessary.

If wiring connection is OK:
- Check voltage supply of Motronic ECM power supply relay -J271-. Testing and Inspection
- Check activation of Motronic ECM power supply relay -J271-. Testing and Inspection

Checking voltage supply
- Switch ignition off.







- Disconnect power supply relay (arrow) below left cover at bulkhead.

NOTE: To remove the protective hood for vehicles with a dome brace, disengage the relay carrier at the bulkhead and swing it downward. Disconnect additional harness connectors at the Mass Air Flow (MAF) sensor, if necessary.







- Connect multimeter for voltage measurement as follows.

Relay carrier below left cover, Measure to
at bulkhead Terminal
1 Engine Ground (GND)
3 Engine Ground (GND)

- Specified value: approx. battery voltage

If specified value is not obtained:
- Perform following tests marked with dots:







- Check fuse S10 (in fuse holder, position 10).







- Check fuse S134 (110 A) in main fuse box/battery.
- Check wiring connection from B+ (terminal 30) via fuse S134 and fuse 10 for voltage supply of Motronic ECM power supply relay -J271- (below left cover, at bulkhead) for open circuit.

Checking activation
- Switch ignition off.







- Disconnect power supply relay (arrow) below left cover at bulkhead.

NOTE: To remove the protective hood for vehicles with dome brace, disengage relay carrier at the bulkhead and swing downward. Disconnect additional harness connectors at Mass Air Flow (MAF) sensor, if necessary.







- Connect multimeter for voltage measurement as follows.

Relay carrier below left cover, Measure to
at bulkhead Terminal
5 B+

- Switch ignition on.
- Specified value: approx. battery voltage

If specified value is not obtained:
- Switch ignition off.
- Connect VAG1598/31 test box at wiring harness to Engine Control Module (ECM) but do not connect ECM. Scan Tool Testing and Procedures







- Check following wiring connection for open circuit and short circuit to Ground (GND) and B+:

Relay carrier below left cover, VAG1598/31 test box
at bulkhead Terminal Socket
5 21

- Repair open circuit in wiring or short circuit if necessary.

If no malfunctions are detected:
- Replace Motronic ECM power supply relay -J271-.