Hello all - I am new to the Audi world and am trying to learn the lingo, so please bear with me as I learn all I can.

I recently became the owner of a 2001 Quattro with the 2.8 L engine and some known issues. I do not know the extent of any prior diagnosing, so I'm starting at this from a fresh perspective. I would also consider myself an amateur in maintenance and repair, able to do most of the basics, but with an IT background my curiosity also makes me want to figure things out on my own. I did search the forums, but there wasn't anyone else with a similar experience with this list of issues that I could find.

I'm in Pennsylvania, so a Check Engine Light is a fail for the emissions inspection, so as long as I keep the car under 5000 miles I'm okay. I would still like to get this light out if I can. I did purchase a AUTOPHIX 7610 OBD2 Diagnostic Scanner to scan codes. I also cleared them to see how fast they come back. The CEL comes back immediately after the second engine start. This makes me wonder if there is an electrical or computer issue due to the volume of codes and how fast it comes back. I verified that the fuse (#34) is functional (continuity tests of the fuse itself).

Here are the codes, in order:
P0036
P0056
P0130
P0134
P0136
P0140
P0154
P0156
P0170
P0173

They come back as O2 Sensors, Fuel Trim, and Heater Control Circuit.

One new thing that I did yesterday, but haven't tested to see if the light comes back on, is I cleaned the MAF sensor with Throttle Body Cleaner. There was some soot-like materials in that part when it was cleaned. I did allow it to fully dry before reinstalled. However I haven't driven it yet to see if the light makes an appearance.

Anyway, lots of info there all at once, but I do appreciate any guidance on where I could start on this one. Thank you.

 

To save time it would help the forum if you defined each code so everyone doesn’t have to look them up.

 

Great point. I apologize for missing that.

Here are the codes, in order:
P0036 - Heater Control Circuit Bank 1 Sensor 2
P0056 - Heater Control Circuit Bank 2 Sensor 2
P0130 - O2 Sensor Circuit Bank 1 Sensor 1
P0134 - O2 Sensor Circuit Bank 1 Sensor 1
P0136 - O2 Sensor Circuit Bank 1 Sensor 2
P0140 - O2 Sensor Circuit Bank 1 Sensor 2
P0154 - O2 Sensor Circuit Bank 2 Sensor 1
P0156 - O2 Sensor Circuit Bank 2 Sensor 2
P0170 - Fuel Trim Bank 1
P0173 - Fuel Trim Bank 2

 

Looks like all your O2 sensors are done and it’s affecting your fuel trims which makes sense.

 

I cleared the codes, drove around for little bit, and parked. Couple days later started car and a few seconds after starting the CEL came back on.

Did another scan and the list isn't as extensive this time:

P0056 - HO2S Heater Control Circuit Bank 2 Sensor 2
P0036 - HO2S Heater Control Circuit Bank 1 Sensor 2
P0136 - O2 Sensor Circuit Bank 1 Sensor 2
P0156 - O2 Sensor Circuit Bank 2 Sensor 2
P0154 - O2 Sensor Circuit No Activity Detected Bank 2 Sensor 1

I also ran the Autophix 7610 to run a live feed of everything while the engine was running. This is some of the data I observed (I have screenshots if that'd better though):

Fuel System 2 Status - OL_Fault. (is this normal?)
Short Term Fuel Trim Bank 1 - the percentage would fluctuate greatly from a low percentage up to 99%
Short Term Fuel Trim Bank 2 - same as Bank 1
Air Flow Rate from Mass Air Flow Sensor - 0.4lb/min
Oxygen Sensor Output Voltage (B1-S1) - 0.74V
Short Term Fuel Trim (B1-S1) - percentage would fluctuate to both positive and negative percentages as the voltage above would change
Oxygen Sensor Output Voltage (B1-S2) - 0.435V


I purchased a bottle of Catclean to see if that could possibly clean off the sensors to help things. One thing I failed to note earlier, but I believe it's also a common issue, is that the engine is also a slow burner of oil, so maybe enough oil has been burned to clog the sensors? The engine also has > 200k miles, but I don't know the age of the sensors, so they may also just be well beyond their lifespan.

 

Are you getting any oil drips on the ground or smell or see oil burning from the engine compartment? We’ve had many 2.8’s come through the shop and all of them didn’t burn oil out the tail pipe but leaks from the valve cover and cam chain tensioner gasket. The tell tail sign that your gaskets are done is oil collecting in your spark plug wells. That’s most likely where all your missing oil is going.

As for the codes, everything is pointing to the O2 sensors.

 

I agree with Cyber, and it sounds like your O2 sensors are dead or dying, which throws off your fuel trim. The heater control circuit is related to that and should go away with new sensors.

A word of advice: Do NOT waste your time with cheap O2's. I threw on some $26(ea.) closeout sensors from Rock Auto and was happy to get through inspection, but they died less than two months later and I did it all over again but with quality Bosch ones (also from Rock Auto) which I have two years on now.

It's also worth doing right because poor fuel trim that is excessively off or done long-term can trash your catalytic converters.

 

Hello all -

I have a happy and sad update.

I was finally able to acquire brand new Bosch O2 sensors. I had them installed yesterday and the CEL went out (or the tech turned it off, he didn't specify). In the past, it would come back on by the second start so during my 75+ mile journey back home, I made a few pit-stops to other stores, so my car was started and stopped 4 times before being parked for the night. Thought 'great, this finally worked!' Not sure if the placebo effect, but it felt like it ran a little smoother too.

Today, went to leave and the CEL immediately came back on. This time though, only one code via the Autophix 7610 device:

• P0170 Generic - Fuel Trim Bank 1

Started/Stopped the car 2 more times and it didn't go back off.

 

Sounds like you've made some headway.

I'm wondering, how many miles does your engine have and do you know if the fuel injectors were ever cleaned & balanced? At higher mileage, they can definitely have debris at the injector filter, or one could be stuck open / dribbling... I will say that dirty injectors usually results in slightly rough running especially at idle, but can definitely throw these fuel trim codes if one is stuck open (or closed), dribbling, or clogged to an extent.

DesertSage and I have had our 12v injectors cleaned and the before / after report provided by the cleaning shop usually is insightful.

 

Currently it's at 203,000 miles. Sadly, I have no history information on the injectors.

I used the Autophix VW menu to get more details on the code, I think. Here, it says
P117600 O2 Correction Behind Cat, Bank1 Control limit reached.