Dodgy O2/Lambda Sensor

[lozzyho]

Hi all,

First post so please be gentle!

I've recently had the dreaded Engine Management warning light on my 2013 A6 (2.0TDi 177). I've used my OBDII reader to get the following fault code:

P2196 - O2 Sensor Signal Stuck Rich Bank 1 Sensor 1

I cleared the fault to see if it was a fluke (wishful thinking I know) but it has happened 3 times now in 3 days, so I'm guessing (hoping) it's just a dodgy lambda sensor in front of the DPF/Cat.

Here's the thing, though. On each time it has happened, it's always been during a period of sustained gentle engine braking (20 seconds or so) on the motorway, going from about 60mph to 40mph in 4th gear. Under these conditions, I'm pretty sure there's very little, if any, fuel in the exhaust unless there's something else at fault.

However, the car has no other symptoms at all. It's running well, performing well, no smoke, great fuel economy (53+ mpg) and there are no other fault codes. Obviously, it's a diesel so I'm guessing it's unlikely to get a rich enough fuel mixture to genuinely trigger that sensor reading. I don't horse the car or treat it harshly, and it's had an easy life in the 30K miles since I've owned it. It's been serviced by Audi all its life, and its last service was about 7,000 miles ago.

So am I safe enough to assume it's a faulty lambda sensor, or bad connection, or do the circumstances point to something else?

BTW, the car has done 55K miles, so the sensor isn't due to be replaced.

Any advice much appreciated.

[Olio]

Just had mine replaced. Same warnings, same (absence of) symptoms.

Have it changed by an indy, so you've got peace of mind.

Those probes seem prone to failure. They are supposed to last 250,000 km or so.

[lozzyho]

Just had mine replaced. Same warnings, same (absence of) symptoms.

Have it changed by an indy, so you've got peace of mind.

Those probes seem prone to failure. They are supposed to last 250,000 km or so.

Thanks Olio, that's good to know.

I did wonder whether the emissions fix was partially to blame, but a) I doubt it and b) they'd never admit it even if true.

How much did you pay at your Indy? I got quoted £205 all-in.

[Crasher]

Those sensors fail with or without the stupid recall but I will repeat again, if you have not had the recall done, don't!

[Olio]

£205 is £10 cheaper than what I've paid, so sound about right.

[Crasher]

The sensor is £174.52 inc. VAT genuine or £140 for a Bosch from ECP.

[lozzyho]

£205 is £10 cheaper than what I've paid, so sound about right.

Thanks Olio and Crasher

[lozzyho]

For posterity, this problem is now fixed with a replacement lambda sensor. I replaced it with a Bosch equivalent part from Mister-auto for ~£90 and fitted it myself.

Fitting it is a doddle: open the bonnet and the Cat/DPF is beside the engine near the right wheel. On top of that is the Lambda sensor. Get a good quality 22mm lambda sensor socket (I got one from Amazon for £10) and it'll save you cutting the cable off the old one to get it undone. Then just use a ratchet driver (or torque wrench) with an extension head on it and the job will take you 10 minutes tops. Last step is using an OBDII reader to clear the fault code.

The old sensor was probably just sooted up. I've cleaned it thoroughly with switch cleaner and kept it in case it can be used again.

And then the very next day, I get a letter from Audi telling me that if there's any fault with the exhaust system after the recall, they'll "consider" contributing to the cost out of good will!

[johnro79]

Has anyone tried cleaning and using the old one?

[lozzyho]

I kept mine aside in case it ever happened again, and if it did then I was going to try and clean and refit the original. I had read speculation that the sensor coking up was a symptom of the EA189 emissions fix, so I half expected a recurrence, but it's never happened.

On the other hand, it's VERY easy to try. I've just changed my car for a late '17 version so if you PM me your address I'll send my old one by post.