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

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

Special tools, testers and auxiliary items required
- Multimeter V.A.G 1526 or equivalent.
- Test Box 105 Pin VAG1598/42.
- Adapter Lead Vag1598/39 VAG1598/39.
- Adapter cable V.A.G 1598/39-1.

NOTE: The Motronic Engine Control Module (ECM) Power Supply Relay J271 supplies voltage to the ignition coils with power output stages as well as the Engine Control Module (ECM) J623 at pin 3 and a few additional components. With the ignition switched on, 12 Volts must be present at the respective ignition coil connector, terminal 1.

Test requirement
- The fuse for the engine electronics OK.
- Battery voltage at least 12.5 V.
- The Ground (GND) connections at the engine and transmission OK.
- The ignition is switched off.

Test sequence
- Remove the rubber seal in the direction of the - arrow -.







- Remove the plenum chamber cover - 1 - .
- Using a screwdriver, remove wiper arm caps - 3 - from wiper arms.
- Loosen wiper arm nuts - 4 - several turns.
- Loosen wiper arms - 2 - from wiper axle by tilting slightly.
- Remove wiper arm nuts completely and remove wiper arms.







- Remove securing clips - 1 - and cowl - 5 - .







- Remove the screws - arrows - and cover from the E-Box in the plenum chamber.







- Using a screwdriver, remove the retainer bar - arrow - and Engine Control Module (ECM) J623 and position aside.







- Remove the Motronic Engine Control Module (ECM) Power Supply Relay J271 - 2 - from the E-Box.
- Remove the Motronic Engine Control Module (ECM) Power Supply Relay J271 - 2 - from the E-box.







- Connect the Test Box 105 Pin VAG1598/42 to the wiring harness of the Engine Control Module (ECM) J623. The ECM is not connected.
- Using the Test Box 105 Pin VAG1598/42 and Multimeter V.A.G 1526 A or equivalent, check the following wiring connection for an open circuit.

Relay carrier position 2 Terminal Test box Socket
4 69

Specified resistance 1.5 Ohms max.

If the specification is not obtained:
- Check the wiring for a short circuit to Battery positive (+) or an open circuit.
- If necessary, repair the wiring connection.

If no malfunctions are found in the wiring:







Checking voltage supply
- Using the Multimeter V.A.G 1526 A or equivalent, check the following wiring connections for voltage.

Relay carrier position 2 Terminal Measure to
1 Engine Ground (GND)
2 Engine Ground (GND)

Specified value: approx. battery voltage.

If the specified value is not obtained:
- Using the Multimeter V.A.G 1526 A or equivalent, check the wiring connections for an open circuit.
Specified resistance 1.5 Ohms max.

If no malfunctions are found in the wiring:







Checking wiring connection
- Using the Test Box 105 Pin VAG1598/42 and Multimeter V.A.G 1526 A or equivalent, check the following wiring connection for an open circuit.

Relay carrier position 3 Terminal Test box Socket
2 3

Specified resistance 1.5 Ohms max.

If the specification is not obtained:
- Check the wiring for a short circuit to Battery positive (+) or an open circuit.
- If necessary, repair the wiring connection.

If no malfunctions are detected:
- Replace the Engine Control Module (ECM) J623.

Assembly is performed in the reverse order of the removal, note the following:

Final procedures
After repair work, the following work steps must be performed in the mentioned sequence:
1. Check the DTC memory.
2. If necessary, erase the DTC memory.
3. If the DTC memory was erased, generate readiness code.

- End diagnosis and switch the ignition off.