EGR Valve Fault

[Klaus Ludwig]

We have tried injecting 12V at ECU plug pins T60/19 and T60/04 with ECU plugs and battery disconnected. The EGR valve opens fully - which is a good test of the loom. If our EGR valve (driven by a 12V PWM motor) is supposed to open fully during a VCDS Output test then quite clearly the ECU is not giving the output that it should - for whatever reason.

Earlier in this thread I mentioned that we had no earth continuity at T6/03 (EGR valve plug) which we should have according to the current flow diagram. I have since discovered that this point is earthed via the ECU which explains the lack of earth continuity with the ECU plugs disconnected.

As our EGR valve is only opening very slightly during a VCDS Output test we will try getting at least a voltage reading across the EGR valve motor which we haven't done yet due to restricted access.

Running out of ideas and reputable ECU specialists.

 

[Klaus Ludwig]

We would be extremely grateful if anyone could confirm for definite if our EGR valve is supposed to open fully during a VCDS Output test. We are working on the assumption that it should.

Our EGR valve is driven by a pulse wave modulated 12V motor. It only opens very slightly during a VCDS Output test. It is free to move by hand and we know that it opens fully if 12V is fed into the relevant pins on the ECU plug as per our previous message.

Our next plan is to measure actually what voltage we are getting across the EGR valve motor during a VCDS Output test. Not sure yet if we will try hiring a scope.

Finally, does anyone know if Canbus is involved with the EGR valve in any way? I believe that our valve uses a Hall Effect Sensor to give a 0.5V to 5V feedback signal, but am not clear if Canbus is involved. I am assuming that the latter may be relevant if we are not using an OEM EGR valve.

 

[Crasher]

All the ones I have actually tested where I could see the operation have fully opened.

 

[Klaus Ludwig]

Thanks @Crasher - much appreciated!

Still think we have an ECU issue and also it is clear that fault P0403 (EGR malfunction) which is what we have, is listed on the Bosch website as a typical fault for our particular ECU.

As far as I can see on VCDS there are 3 setup operations related to the EGR system.
1) Reset of EGR valve (under adaptations)
2 EGR valve basic settings (which for our car seems to be under engine / group 123 and out of 4 dispalyed measured value fields seems to only use field 1 and field 4. Field 1 being Lamda % and field 4 being voltage (which appears to be the 0.5 to 5V EGR valve position feedback)
3) EGR system basic settings (engine running)
Any tips related to the above would be much appreciated. VCDS Wiki does not seem to mention EGR valve set up on diesel engines that I can find.

Unfortunately, we have not had much luck with the two "good" ECU specialists that we have sent our ECU to (ECU Testing Ltd & ACtronics). The first one was unable to complete all necessary tests, but their comm's were excellent. The second one did not load test the ECU output to the EGR. Looks like we only have Bosch in Germany left as a realistic option?

 

[Crasher]

Both the ones you mention have failed me, one is a local legend. I have used Bosch in Germany twice, they failed to spot a fault until I sent it back again and then said it was unrepairable offering me a new one for more than a genuine VAG new unit.

 

[Klaus Ludwig]

Fitted a Pierburg aftermarket EGR valve from Eurocarparts, performed a basic setting and crossed fingers. Not convinced that the voltage in field 4 of Engine group 123 (which I believe is 0.5 - 5V EGR valve position feedback) comes anywhere close to matching the expected value based on the EGR motor duty cycle. The car has been out for a few short trips with no EGR valve warning as yet.

It is not clear to me that just switching on EGR basic setting (Engine group 123) is the correct method for carrying out EGR valve alignment on our particular vehicle. I have not yet found any evidence of others doing this. For petrol engines the method is well documented in Ross Tech wiki using Engine group 74 - which we don't have. In the latter case, field 4 of Engine group 74 apparently announces the successful completion of the adaptation.

 

[Klaus Ludwig]

P.S.
Our new Pierburg valve opened a max of approx ONLY 1.5mm during a VCDS Output test. The max possible valve lift measured with a DTI was 5.36mm when the Pierburg valve was opened manually via the gears (plastic cover removed) and a lift of 5.36mm is also achieved when putting 12V directly across the motor terminals (equivalent to 100% duty cycle).

The fitted Pierburg EGR valve opens slightly further than the original valve during a VCDS Output test and that fact may be just enough to stop a fault indication???.... We will see. It definitely does not open anywhere near fully during an Output test.

Would be very interested to hear any opinions on /experience of using Engine group 123 to carry out EGR valve alignment under basic settings. This is the group which comes up via the basic settings menu for EGR valve basic setting on our vehicle.

 

[Klaus Ludwig]

After over a week with the new Pierburg exhaust gas recirc valve in place. No more associated EGR faults appearing. Briefly monitoring VCDS measuring block group 123, field 4 (which is the exhaust gas recirc valve position signal) we have noted that this value now goes from 0.76 to 3.7 V between engine stopped and revving engine - which is significantly more range than was the case originally. I am assuming that some self tuning may have taken place? Still not sure why the original or new EGR valves did not open anywhere remotely close to full open during the VCDS output tests. The original valve barely moved at all - even though it was free.
Onwards and upwards. Time to move on to the next thing!