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I have very weird problem with my WBO2 lambda values. At first I thought I had a leak either in intake or exhaust side, but that has now been counted off.

These lambda values I get, both sides equal:

At start lambda 0.8-0.9.

When warm-up enrichment cease lambda rises to 1.0.

After few minutes of idle lambda 1.1.

Increasing revs idle-4000 rpm, car stationary, lambda rises to 1.2-1.3

Over 4000 rpm ( exact switching point unclear ) lambda drops to 1.0!

While there were no mechanical causes to this I stated to look for electric ones. What makes fault finding difficult is that I have reprogrammed Motronic and I really do not know which fault codes have been blocked. I asked just NBO2's to be blocked, but so far I haven't got info if all oxygen sensor related were...

So I started with OBD Manual's code P0130...:

Work instruction:

1. Check reference voltage on component. OK

2. Check reference voltage on control module. Unable without that test adapter

4. Check wiring for short circuit to ground. OK

5. Check wiring for open circuit. OK

But 3. Check wiring for short circuit to B+. Measured following voltages:

Pin II/9 and gnd 2,5V

Pin II/15 and gnd 2,96V

Pin II/2 and gnd 0,35V

Pin II/5 and gnd 0,35V

Right bank shows similar values. According to work instruction all of these should be 0V. ( Although I did measurement with cold engine... ) Corrective action is to repair wiring & correct the cause of damage.

Now the million dollar question:" Where that short to B+ may be?", if it's not in the WBO2 wiring, which I have just replaced without any help. Or is my Motronic toast? If yes, why?

Thanks for even trying to help...!

PS. '01 turbo engine, EVOMS tune. New WBO2 sensor. This problem did not occur before the Motronic was tuned in January, neither right after that. It has developed during the spring, first symptoms I noticed in end of March when changing better flowing intake parts and doing Durametric loggings after that. Because of this the car failed state smog test and is now prohibited to drive until it passes...

EDIT: Did some more fault seaching.

According to fault code P0103 MAF B+ check OK.

According to fault code P0112 & P0237 ( or 0238 ) IAT & MAP B+ check not OK, found +5V.

Disconnecting connectors ( breaking points ) X59 1/2/3 ( = separating the engine ) does not help, ie. the fault is not at engine wiring loom.

Disconnecting Motronic connectors C/D/E and leaving only A & B, power feed and WBO2,, does not help.

Removing fuse C1, engine electronics does help...

Is there a way to get the Motronic tested for internal faults? And also repaired?



EDIT: Back then I forgot to add the solution for this case. Eventually it was incorrectly installed (ie missing) engine wiring loom grounding wire.

Edited by pete95zhn
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