Seat Leon.
Year 2004.
1.9TDI ASV engine.

Reported to be running rough, no power. I didn’t test drive it.

Came in with the following fault codes.
17957 boost pressure regulation valve N75 open or short to ground.
17849 EGR valve N18 open or short to ground.
17660 commencement of injection valve N108 open or short to ground.

The codes would not clear. I checked supply to N75 and N18, both ok. Checked on the return sides of both solenoids while unplugged and had 3.7v (from the ECU)which is about right and I think indicates the wiring was ok. My first thought was an ECU fault. Since the solenoids had good supply and the returns back to the ECU seemed ok the fault codes should have cleared.

The above was a quick check before bringing it into the workshop. Moved it inside later for testing. Still same codes. The three faulty circuits are fed from fuse 34 which checked ok. I did a quick general check around the wiring and removed ECU and took the covers off the ECU plugs for back probing. At this stage the fault disappeared. I don’t suspect the main relay because fuse 34 was ok with the fault present.
The car has only 60K KMs and all the wiring and connections etc are mint.

It is not fixed but I can’t get it to fault again. I have wiggle tested this to death. I have opened the ECU and flexed the board with the engine running.

Anyone seen this before? Any thoughts?

Thanks