TimeOrMoney

I got the following intermittant problems with VAG-COM on a 2.8 30V:

4 Faults Found:
16518 - Oxygen (Lambda) Sensor B1 S1: No Activity
P0134 - 35-10 - - - Intermittent
16538 - Oxygen (Lambda) Sensor B2 S1: No Activity
P0154 - 35-10 - - - Intermittent
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

So I could:
1. Reset and see if they come back,
2. Do all the fancy block diagnostics to see how "old" they are, etc.
3. Don't waste the time, just replace them. Car has 140K!

I'm thinking just do it (#3). Might increase gas mileage a tad, anyway. Should I get the universals and save some bucks?

Danomatic93

Try resetting the codes. They will likely come back after two starts.

If you have a meter, check the resistance between the white wires on the oxygen sensor. Should be around 10 ohms. If it's in the 200 ohm range, the heater is dead and will give you a internal resistance too high fault.

Since these are the primary (pre-cat) sensors I would order up a set. These are the ones that determine your fuel map, the important ones.

eejimm

I would also look around to make sure there's not a connector loose, or an ECU fuse blown. Suspicious to have booth sensors and their heaters go bad at the same time. There is common power to the heaters, no common grounds, though.
Jim

TimeOrMoney

I just reset. This intermittant thing leads me to think it could be a glitch, but we'll see. Wet or corroded connectors could theoretically make either the heater or signal paths have higher resistance, so that's a possibility. I'll probably order new sensors anyway, as I've gotten better MPG on all the over 100K cars I've replaced them (front sensors) on. These are narrow band sensors, so universals will work, assuming I can clean/reuse the old connectors.

johnkk

Agree. I reset several times until the light goes on every week or so and gets annoying. I replaced passenger side when it became a daily light. Driver side now throws a light about once a month. Probably get almost another year before the light is daily.

SloopJohnB@mac.com

STFA. There are universal sensors and universal sensors as I recall. Something about response time on the audi sensors...IIRC BD had some Bosch part numbers and tech explanations but I'm too lazy to look them up.

Now, of course karma will cause my own sensors to fail and I'll have to look it up anyway.

tenspeed

Does Audi use all four O2 sensors for fuel trim?

Some cars use the upper sensor(s) for the trim and the lower sensor(s) for the health of the cat. The lower sensors can be replaced with a dummy load or placed in a spark plug extender to prevent the "Check Engine" indication.

Replacing the upper sensors at 100K is a good thing for fuel economy. Sensors get slow as they age. IMO, the money spent just to monitor a healthy cat could be put to better use.

GTA_Driver

I'm pretty sure that Audi does the same thing.

eejimm

Think about it - the fuel trim has to come from only the upper ones, otherwise it won't be an accurate reading of the engine's A/F mixture. The whole purpose of the cats is to burn off excess hydrocarbons, which will change the A/F ratio coming from the engine, and would make the engine run rich if the fuel trim was looking at the lower sensors.
The lower ones are only there to check the operation of the cats themselves.
Jim

SloopJohnB@mac.com

Nope..just the upper ones.