Might be a dumb question, but I think I may be having an O2 sensor problem but need to know, does a 2000 A4 Avant Quattro (1.8T) have two O2 sensors or one? Can't find the downstream one or wires to it if it is suppose to a have one.

 

2 sensors. Why do you think you are having a problem? CEL on? What trouble codes are you seeing?

 

I am just copying and pasting a post by me from another forum below but this will give you the just of the problem... Thanks for replying.

I have a 2000 A4 quattro Avant with approx 118K mi. I have been getting the P1136, Long term fuel trim.....too lean code on and off for a couple of months. Engine is idling a little rough, MPG is down slightly, sometimes a black carbon looking smoke in exhaust at idle.

I have had both the MAF sensor and turbo recirc. valve replaced at the "advice" of the dealer. The code still was appearing until I picked it up from the shop yet again and noticed that the light came on approx 5 seconds after startup, much quicker than it normally takes once reset, (the shop had reset it).

I put my scan tool on it and I am no longer getting P1136 (lean mix) but 10 different codes all pertaining to O2 sensors, sec air sys, turbo valves, etc....and a lot of short to ground codes.

Could a faulty O2 sensor cause all these codes (see below)?

I have just replaced the upstream O2 sensor, reset the codes and still getting the error codes. Could there be some sort of a system relay bad? or could a faulty downstream O2 sensor cause these codes? I have looked for shorted wires, loose connectors, etc. but found nothing. I am at my wits end with this one and any help will be appreciated.


P1425 Tank Vent. Valve short to ground
P1117 O2 sensor heater circ, bank 1 sensor 2 short to ground
P1435 Sec. air inj sys pump relay circ short to ground
P1421 Sec air inj sys valve circ short to ground
P1289 Turbo bypass valve short to ground
P1473 EVAP Emis cont LDR circ, open circ
P0102 Mass or Volume Air Flow a Circ low
P1115 O2 sensor heater circ, bank 1 sensor 1 short to ground
P1114 Bank 1, sensor 2 Internal resistance too high
P0140 O2 sensor circ no activity detected, bank 1, sensor 2.

 

I counted "short to ground" six times. I think there is a short to ground.

My guess is that they fuxored something when they were working on it. Take it back asap.