Fault Code OBD II 0155 (O2 Sensor)

[Sir WIll]

Ladies and Gents,

The only fault code I am getting from the A8 is in regard to the 02 sensors.

OBD II P0155 Oxygen Sensor Heater Circuit Malfunction (Bank 2, Sensor 1)

Now this tends to come and go, I have days without the engine warning light on the dash. Then it pops back for a while to say hello then goes again.

Car drives fine, no problems and whether its on or not makes no difference to the driving of the car. That's all well and good but I would like to have it cleared so it stops annoying me!

Are we looking at here a case of a Lambda sensor swap, wiring or perhaps an exhaust leak (Though cannot hear anything)?

[Sir WIll]

Aha, think I have found the reason.

Started up tonight and its sound quite fruity! Thought to myself this is not a sports exhaust so had a look.

A quick look shows that under the engine drivers side the exhaust I think Pre Cat has been wrapped with black cloth, looks like a cheap repair to me.

Anyone point me towards a diagram of the exhaust as I cannot quite tell if its the downpipe, cat or perhaps a flexible joint that's gone and will need to be replaced.

[Architex_mA8tey]

Here you go - top manifold in the first picture of the upper image and cat/pipe in the lower image







.

[Sir WIll]

Good man, thanks for that.

Looks like number 3 on the second picture, where the bulge is I presume pre cat. Looks like one whole part to me also so the whole lot may need to be changed.

The bulge pre car is wrapped in black cloth so I think someone has done a little repair!

Anyone have the right part code as its time to work out whether to fix myself or see what ATS/ Kwik Fit would want to charge.

[Sir WIll]

A little google and eBay suggests:

AUDI A8 Catalytic Converter Exhaust 90909 3.7 ltr 3/1999-2/2001

Last time I replaced a cat Kwik Fit were damn cheap so perhaps worth a quote at least.

Though does sound lovely right now

[Dezzy]

Down pipes from the manifold. Well obvious would be second hand parts give A8Parts a call and do it yourself if possible, ATS and the likes might be able to source pattern parts but get a quote first if that's the way you choose to go, as it could be time consuming. The flange nuts / bolts from down pipes to cats get hot, cold, hot,wet ect and rot, and flanges to the cats.
Manifold to downpipe is not too bad, inner arch out for access. It might be as cheep to use a local specialist exhaust that can bend some stainless tube to suit.

[Sir WIll]

I will pop the old girl into the local Kwik Fit so they can get it on the ramp and at least have a look.

Get a quote and take it from there.

[Architex_mA8tey]

Part number for item 3 - RH side is -

part number 4D0 253 012 PX

But be warned its looking like about £860 on the parts prices I have and that may well be plus VAT

Try David or Carl at A8 Parts as they've had some 3.7's in there and may well have a 2nd hand one at much reduced cost

[ainarssems]

I am afraid there are no cheap aftermarket replacements available as far as I know. In your case as the cat is working fine it's probably best to cut out damaged piece of pipe and weld a new one in.

[Dezzy]

I did think that it might be a no no from one of the national companys.

I had trouble with the parts aft of the cats, the cats had been welded to the down pipes at some point and flanges welded to the cats, a bit of a mess. A local tyre and exhaust place has a tube bender and stock stainless tube (although not sure where they get it but i could stick a magnet to it) cut the section out and bent a bit of stainless tube to suit. I had some Flanges cut on the laser and supplied the exhaust place with these. Some were hole and some halfs, the halfs could be placed over the tube and welded together so the fluting didn't need cutting off and cause another problem.