Audi Repair: Oxygen Sensor, oxygen sensors, audi cabriolet

Question
QUESTION: I have a 1996 Audi Cabriolet.  The check engine came on and the code indicated baed oxygen sensors.  My mechanic replaced both before the convertor.  The check engine light came on again indicating that "Bank 1, Sensor 1" is not functioning.  My mechanic blamed the part, and replaced it.  Still not working - code P0134.  He blamed the part again.  Replaced yet one more time this morning...and it's still not working.  Auto store blamed carbon build-up.  Any thoughts?

ANSWER: I have heard of one bad O2 sensor, but not 3.  Sounds like you have  a problem with the wiring.  Cheers,  Jan

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QUESTION: Hi Jan,
Thanks for all of your help on this.  Okay, so in an effort to determine if the wiring was bad, we unplugged the oxygen sensor from the harness, and plugged a new one in just to check the wiring.  While the Oxygen sensor was not actually installed in the manifold, it did heat up.  I'm assuming that it is actually getting power - so, the wiring appears to be okay.  

So, I now know that there is actually power going to the sensor and the sensor itself is working.  There is some disconnect with the o2sensor being installed.  I mean, the sensor works, the power is going to it, there's just something about it sitting in the manifold.  I'm thinking it's something in there.  What are your thoughts?

ANSWER: The heating up of the wire does not mean the sensor itself is OK.  The heating wires are only half of the equation, the sensor wires the other half.  When you plugged the last sensor in could you re-set the light?  I would double check the sensor is the correct one for your car, and also verify if there are any shortcircuits in the wiring.  I have never heard of any build up in the manifold causing this kind of issue.  Jan

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QUESTION: Hi Jan,
Sorry to keep bothering you on this.  So, the other half - the 'sensor wires', how could one tell if those are bad?  We were able to re-set the light, but within minutes it came back on with the same code.  The code is 'no activity detected.'  My mechanic did some test on the sensor - digital mulitmeter that says it's working.  Is there a way to actually clean the housing where the sensor sits or no?  

Answer
There is no housing where the sensor sits, it is located right in the exhaust manifold down pipe.  I don't see a way for anything to obstruct the sensor.  Are you sure it is a broadband O2 sensor, and not some aftermarket 'universal' O2 sensor that has been obtained?  The universal ones have been troublesome.  Let me know,  Jan