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

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







Special tools and equipment
- VAG1526 A
- VAG1594 A
- VAG1598/31

NOTE: The Motronic engine control module (ECM) power supply relay -J271- supplies the ignition coils with output stages as well as the engine control module on Pin 121 with power.

Test sequence







- Disconnect cover -1- on left in engine compartment.







- Unbolt coolant expansion tank (arrow).
- Disconnect electrical wiring to Engine Coolant Level (ECL) warning switch -F66- on bottom of expansion tank.
- Lay coolant expansion tank with connected coolant hoses -1- to -3- aside.







- Remove bolts (arrows) on left cylinder head.
- Disconnect 4-pin connectors -4- to -6- on ignition coils.

NOTE: For further testing, the multimeter is attached to an ignition coil connector.







- Connect multimeter as follows to measure voltage.

Connector Measure to
terminal
1 Engine ground

- Switch ignition on.

Specified value: approx. battery voltage

If specified value is not attained:
- Switch ignition off.
- Pull off rubber seal of plenum chamber cover.







- Remove plenum chamber cover -1- toward front (arrows).







- Pry off both trim caps -3- with a screwdriver.
- Undo hex nuts -4- a few turns.
- Release wiper arms -2- from pivot shaft by tilting them slightly.
- Remove hex nuts completely and remove wiper arms.
- Disconnect retaining clips -1- and remove air cowl grille -5-.







- Remove cover for electronics box (plenum chamber) (arrows).







- Lift off engine control module retaining clip using a screwdriver (arrow) and move control module to side.
- If installed, unclip transmission control module retaining clip and place control module on one side.







- Disconnect power supply relay -2-.







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

Relay carrier in electronics box, Connection of ignition coils
plenum chamber, position 2 terminal
terminal
8 1

- Repair open circuit, if necessary.

If no wiring malfunction is detected:
- Check voltage supply of Motronic Engine Control Module (ECM) power supply relay -J271-.
- Check actuation of Motronic Engine Control Module (ECM) power supply relay -J271-.

Checking power supply







- Connect multimeter as follows to measure voltage.

Relay carrier in electronics box, Measure to
plenum chamber, position 2 terminal
1 Engine ground
2 Engine ground

Specified value: approx. battery voltage

If specified value is not attained:
- Check wiring connections.

Checking actuation







- Connect multimeter as follows to measure voltage.

Relay carrier in electronics box, Measure to
plenum chamber, position 2
terminal
4 Battery positive

- Switch ignition on.

Specified value: approx. battery voltage

If specified value is not attained:
- Switch ignition off.
- Connect test box VAG1598/31 to wiring harness for engine control module; do not connect engine control module.







- Check for open circuit and short to positive or ground in following wiring connection:

Relay carrier in electronics box, Test box V.A.G 1598/31
plenum chamber, position 2 Socket
terminal
4 23

- Repair any open/short circuit as necessary.

If no malfunction is found:
- Replace Motronic Engine Control Module (ECM) power supply relay -J271-.