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created 30.12.2007

Checking and repairing the ECU’s relay:-

One of the most common fault which cause any of the following is usually down to the relay 30 (the ECU’s relay) being faulty:-

- Erratic idle speed

- Engine running badly at no-load

- Engine stalling for no apparent reason

- Error 0532 ECU voltage too low

- Several errors logged by the ECU

Note: The engine could still be running badly if the ECU relay is faulty and no

errors were logged by the ECU.

If the ECU relay is suspect, then it should be removed and either repaired or replaced. A replacement relay costs about 10-odd Euros or about 10-odd pounds in the UK.

The ECU relay is located in the front boot compartment on the left hand side of the car (arrowed):-

The relay its self can be removed carefully by pulling it upwards away from it’s socket whilst holding down relay 80 (the fuel pump relay) at the same time
. Make sure that you do not break the relay sockets !!

The VAG part number of the ECU relay is 165 906 381, which is shown below:-

This ECU relay also fits the following vehicles:-

- Type 2 T4 (Bus T4, etc.)

- Golf Mk 3 and Mk 4

- Vento

- LT Mk 2

- Audi A4, A6, 100 (1993)

- Audi 80 and 90 (1992-on)

- Audi Coupe

- Caddy (1996 – 2003)

- Passat Mk2 and Mk3, Santana

- Polo Mk2

- and several other VWs

To fix the relay its self, you will have to remove the plastic cover from the relay its self. To remove it you will need to do the following:-

- Use two jeweller’s screwdrivers (one on each side of the relay) to gently prise off the plastic cover outwards from the relay’s base.

- Now lift up the plastic cover upwards away from the relay’s base.

- You should now be able to get at the relay’s PCB.

The most common problem with the ECU relay is usually dried solder joints on the relay’s PCB. These will cause an intermittant (or non-existant) electrical connection between the component(s) and the PCB its self.

The photo below shows (in this case) where there are dried joints on the relay’s PCB, which are indicated by the red arrows:-

The solder joints shown in the photo above shows that there are several dried joints on the relay’s PCB. Notice the difference between the solder joint on the left hand side of the photo and the rest of them.

Note: The relay its self may have different dried solder joints compared to the

one in the photo above.

These solder joints should now be cleaned up and resoldered. Use a soldering iron, solder and a solder sucker to do this. Once those solder joints have been redone, the relay’s PCB should now look like the one shown in the photo below:-

Now compare the two different photos and notice how shiny and complete the solder joints are. This should now fix the ECU relay problem.

Now refit the relay back into it’s relay socket, connect up your diagnostics kit and start the engine.

Now read the fault codes from the ECU and erase them. The engine should then run normally.

This document has been translated (in my own words) by Phil Ade, Saturday 3^rd November 2007.