RMcQ

Seems straight forward. Internal resistance too high (i.e. it is broken/failed/out of spec/whatever) and it needs a new ones.

Should I just buy and replace both pre-cat O2 sensors as VAG-COM is telling me or is there any other explanation I should consider before going to the trouble.

Car is a '01 allroad. Codes do come back after being reset once car runs a while. Mileage is 61,xxx miles.

Here is the exact text:

<b>Control Module Part Number: 4Z7 907 551
Component and/or Version: 2.7l V6/5VT G 0002
Software Coding: 06712
Work Shop Code: WSC 02325
Additional Info: WAUYP64B71N069945 AUZ7Z0Y1611845
2 Faults Found:
17539 - Oxygen (Lambda) Sensor: B2 S1: Internal Resistance too High
P1131 - 35-10 - - - Intermittent
17521 - Oxygen (Lambda) Sensor: B1 S1: Internal Resistance too High
P1113 - 35-10 - - - Intermittent
</b>

robfox4

Sounds fishy. It is unlikely that two O2 sensors failed at the same time, but it could happen. Possibly overfilled with oil, which coated the front O2 sensors, or some other contaminant. The pre cats would probably have prevented the rear sensors from being damaged. If it were a different car I would suggest buying an O2 sensor and throwing it in, to see if it fixes it. However, the front ones are REALLY hard to get to on the 2.7T engine.

"Internal resistance too high" isn't usually masking a different problem. Usually it is a failed sensor. Did you make sure everything is plugged in correctly on the pre-firewall location? From memory, the S1's on each side will be the oval black plugs, while the green and brown ones are the rears for right and left. Again, from memory, so I'm not 100% sure right now, The green and brown S2s and the passenger side S1 will all plug in on the passenger side behind the airbox, while the driver's side S1 plugs in sort of in front of the brake fluid reservoir. Check those, and the wiring, and if all looks good, you might want to replace one at a time to try not to spend too much not to solve the problem.

Hope this helps,
Rob @ MP

skidmark

got them out with a stubby 22 mm wrench but i had my downpipes loose and could get my arm up there. it is funny that both sides went bad at the same time.(and you just chipped around a month before) try some weird gas additive? i have heard a lot of people say that 02 sensors only last about 60,000 miles but i don't know if it is true or relates to audi's.

RMcQ

Still seems weird that both went at one time.

If I want to replace, I guess it is going to be a real hassle. They put them in a really difficult position I understand.

Damn...

RMcQ

but I think I am stuck replacing 2 sensors. I understand that I can buy the same sensor with a VW part number for much less than the Audi OEM part number. I've got to do a little more research.