Why do these OBDII / DTC Fault codes keep coming back ?

[headache56]

Why are these OBDII / DTC Codes coming back to haunt me ?
To cure hesitant acceleration on my 1999 Passat 1.8 Turbo APU engine, I have replaced the:
- EVAP purge value (DTC fault code 17833)
- Turbo Boost N75 valve (DTC 17955)
- MAF (DTC 16486) and the
- Oxygen-Lambda sensor (DTC 17523).

Most of these faults refer to "Short to Ground" but my dealer has not found any common / connected issue using VAGCOM.

I have erased all fault codes with a (Autel) hand held code reader (several times) but after short drives the codes keep coming back. The hesitant acceleration seems to be cured and the only other code not yet fixed relates to the N249 valve (DTC 17697).


Any tips guys (or girls), please, on:

(1)
Is it possible that only VW dealers' diagnostic equipment can erase fault codes ? Realistically, I worry that if I can erase all codes, they are gone for 10 minutes, then reappear, the underlying faults must still be there?

(2)
Is it possible that I have wasted my time replacing the above and that there is a common / connected Short To Ground fault which has not been identified yet ?

(3)
Where is the N249 Boost Pressure Control Valve (it is not shown in my Haynes Manual).

Any steer would be much appreciated.

Thank you
Kevin

[Sam]

Unfortunately, if the codes keep returning, then the problem(s) still remain(s).

[headache56]

Dear MycarsaVW,

Thank you for your response, which was, as I feared.

My local authorised VW dealer has already run a diagnostic for 2 hours (they say) on their dealers' system which I think is VAS, VAGS or a similar wording, NOT VAG-COM. They merely suggested replacing a Turbo and Purge valve (now done).

I asked them if they did not see a common theme in that 4 or the fault codes all referred to "Short to Ground" which kind of implies a wiring fault. They said no.

I am wondering whether an Automotive Electrician / company might have the necessary extra expertise as I do not have much faith in my local VW dealer to fix / understand this difficult problem.

Any suggestions please?

Maybe if I buy a £212 Vagcom kit from ILEXA that might help me identify the problem more accurately?

I am wondering whether the ECU needs replacing at £820 new?

Regards
Kevin

[kenney]

Having looked at the wiring diagram these components have one thing in commen and that is the ECU might be a good idea to have a look at the 121 multipin connector on the ECU

[Sam]

As kenney has stated, eveything goes back to the ECU.

Pop the bonnet and check for any signs of water/damp intrusion. It could be something as simple as a poor connection at the ECU or a bit of damp.

That said, the diagnostic equipment would have struggled to communicate if that were the main problem.

Interesting

[headache56]

Dear Mycarsavw, Kenney, er anyone:-

Thank you. I checked, removed and examined the ECU closely and it all looked remarkably clean. I then noted which of the 121 PINS relate to what components (MAF, N75, N80, N249, G70 and G139) that are showing up with "Short to Ground" ODBII / DTC fault codes.

The applicable PINS are not even close to each other and the wires that come into the ECU are on different sub-looms / different "twigs of the branch" if you know what I mean.

Then, checking a detailed wiring diagram sent to me by Haynes Manuals, I see that all these components share a common wiring connection, which the Haynes diagram describes as :

"E30, Connection 87a, in engine wiring harness "

Any steer please on how I might locate, check or fix this connection would be really apprecaited.

Thank you
Kevin