QuestionQUESTION: I have a 99 VW Passat 1.8T that has the above code. Have since changed the MAF and vacuum hose as advised by Greg (on this forum) but code remain. Also changed the upstream O2 sensor but code remain. Could the downstream O2 sensor be at fault or could there be another underlining issues such as a vacuum leak in another location.
Thanks.
ANSWER: I have seen on rare occasions that the O2 sensor could be faulty. Have you changed the O2 sensor yorself or have it done? Also if you have replaced these items you have to re-set the fault codes using a VAG-COM, the fault codes do not get erased automatically. Since the fault code states electrical circuit problem I would also make sure you are getting the right voltages at the sensors. let me know, Jan
---------- FOLLOW-UP ----------
QUESTION: Thanks Jan. Have all work done at a repair shop and codes were all erased. A couple of follow-up question:
1. What about the second O2 sensor should that be replaced too? (The upstream had changed to white )
2. I'll check the voltages check but what should be the optimum reading?
3. What about the vacuum leak, is that possible?
Thanks.
Dele.
AnswerThe second O2 sensor does eventually fail but usually later than the one in front of the CAT. It is normal for these sensors to have a white color after use. These are three or four wire O2 sensors, two are used to heat a filament, this voltage should be present when the car is running and warmed up. Vacuum leak is possible, but I don't know how likely. You can test the vacuum system for integrity once you remove the vacuum line from the manifold, and attach a vacuum pump to the lines and measure the leak down rate.
