Wife's car
 

1998 A8 w/ 185K.

It's driven only about 100 miles a week for groceries, etc and very conservatively. She's 73 yrs old as am I.

Owned since 9/2007 with very few issues and never a CEL

In last month, CEL came on twice. Both times after car not started for 4 or 5 days. Other than the CEL, car ran with no problems. Reset CEL each time. Looking at repair history from PO shows O2 sensors replaced in 2005.

Codes came up as follows from CARISTA

OBD2 - confirmed:
P1198
P1199
P0160 - O2 Sensor Circuit No Activity Detected Bank 2 Sensor 2

Any thoughts? (Other than why is a 73 yr old guy is still screwing around with an audi)

Do you have access to a VCDS scanner, so that you can pull more precise telemetry? I doubt the car would not start with a simple O2 sensor failure. However, if your CPS or MAF is dirty/defective it could be causing such issues. When is the last time you performed maintenance on the vehicle? i.e. cleaning MAF, replacing spark plugs, changing filters, etc...

​​​​​​'' Both times after car not started for 4 or 5 days." ? ...I believe he meant, after not being driven or started ... not unable to start.

Jim, did the CEL come back after 2 driving cycles after you reset them? If a "problem" persists, it will trip the CEL after 2 "drives" (2 start-run-shutoffs) ... likewise, 2 cycles with no detection of a "problem" will automatically turn off the CEL.

Cheers
Sam

The last time I got an "O2 sensor no activity" fault, the fuse for the upstream O2 sensor (Sensor 1) heaters had blown. The upstreams were both on one fuse, along with the MAF sensor, so I also got a MAF fault. The downstreams, if I remember correctly from my '97 wiring diagram, are on another fuse. If it were the fuse I'd expect you'd get faults for both sides, Bank 1 and Bank 2.

I think you did - below is pasted from http://www.bentleypublishers.com/tec...table.htm17606
P1198

O2 Sensor Heater Circ.,Bank1-Sensor2 Electrical Malfunction

17607
P1199

O2 Sensor Heater Circ.,Bank2-Sensor2 Electrical Malfunction

Check your fuses?

Hi Silver, we've chatted before about my 2000 A8L, which was two cars ago for me. This is my wife's 98, owned long time.

Hill is correct there never was a problem starting. Maybe the verbiage I used was confusing. It starts, runs and behaves normally.

I don't have a VCDS. My Carista has sufficed for what I need, including open, close, calibrate elect park brake on my D3

CEL has been intermittent. Comes on, scan and reset, then drive a week and it's back

Today, I used it for an errand, CEL came on soon after I left the house. Scanned and produced the same codes and I reset. Drove a bit more and scanned, P1198 and 1999 were "pending" reset and drove and scanned again, they were still there. A little more driving and the CEL popped up and included the P0160.

I'm ruling out a fuse as I don't know too many fuses that are intermittently blown. I'm thinking it might be a connector related to the heater circuit but not sure where to look. Is this on the O2 sensor behind the CAT or under the hood? since it's bank 1 and 2, I'm thinking something common such as a connector under the hood. Can anyone give me a location to look?

Thanks

Could be mice?

Sensor 2 is behind the cat. Those wires go up through the floor on each side of the car. You should be able to see them on the inside by pulling up the rug on each side, a simple job. There are connectors there.

I have had mice chew through wires. Melted insulation on wires can go intermittent with shorts to ground or even continuity.

But both sides at once?

Two mice?

Aside from the remote possibility of two mice and both connectors becoming flaky, what is common to them. Where is the fuse for the heater circuit? What number? Is it the same fuse for both banks? The way it's been acting, (ok for a week, then CEL), I wouldn't think it was a fuse, but could the heaters not work at all, then only cause a fault occasionally?

Thanks,

Both downstream (of the cats) O2 sensors G130 and G131 (well, to be more precise, their heaters Z29 and Z30, respectively) are powered by fuse S4 (4th spot over from the right) on fuse row ST4 (4th row [blue] down from the top). I wouldn't think fuses go intermittent, but stranger things have happened. I have had fuses (in non-automotive situations) show continuity when removed and tested with an ohmmeter but unable to pass the required current in service. At the very least you should look at the fuse carefully.

From the wiring diagram, the only other thing I see common to both bank's O2 sensors is that the other 3 wires on each sensor plug into the ECU. Being resistance heaters, also the fact that they're exposed to high heat, it's possible that they can go intermittent as they heat up and cool down. Maybe they both reached the ends of their lives around the same time?