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Hi all, I'm a lowly lube boy at a VW dealership and a very big fan of Paul's methods, and was helping one of the master techs the other day with trouble shooting this problem. The O2 sensor 1/1 (upstream) was replaced around 8 months ago for lean codes, and the car has come back now with the same problem.
One dead end we found was 2.5 volts on the sensor ground at the ECM, but we tested another identical car from the lot and found the exact same voltage down to the millivolts (that's a weird one by itself), so concluded it must be something normal. We tested further and could find no other out of the ordinary signals, and the sensor itself was found to be behaving normally.
Another very unfortunate fact of the matter is that we have EXTREMELY limited freeze-frame data on the VW scan tool system (literally date and time and maybe RPM and system temp if we're lucky).
Any suggestions from any late model German make gurus here, firstly about why there is that much voltage as normal on a supposed ground circuit, and/or what to look for next?
I'm far from a VW guy, new or otherwise. :silly: But I'm not at all surprised to hear that you found 2.5V on that sensor ground circuit. VAG products have been rolling with five wire air/fuel ratio sensors for years now, and 2.5V is a very commonly used 'floating ground' value. It's similar down to the mV because it's regulated and supplied by the ECM.
That freeze frame data sounds like a joke! :lol: I wonder if the Global OBD side of things would have more detailed data? Nissan has similarly frustrating FF data - some PIDs, just not the ones you want. So I sometimes find myself combining the OEM and Global data to get a clearer picture.
Is this lean condition intermittent, or can you reproduce it? Are new model VW's still using additive and multiplicative values?
