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savethestickshift

saveth ... 1/17/2020

2010 Audi S5 Base 8 Cyl 4.20L

Engine

Intermittent O2 sensor codes... have they gone bad? (4.2L V8- 105,000 miles)

i have had occasional fault codes of P2098, P2096, P2196, P2198, and the even more occasional P0161/0141 (O2 sensor heating circuit malfunction) which are all codes for too much O2 in the exhaust. I have been monitoring the situation with an OBDII scanner for months and sometimes I can go multiple weeks with no problems. Other times, it's every other day that these codes come back. To mitigate these issues, I have replaced a fuel injector (that was causing a misfire) and only run Shell Nitro+ gas through the car, I carbon cleaned the engine, checked all my vaccuum lines and replaced them all, and replaced a fuel valve to correct a preexisting P0171 (that has not reappeared). I also had my cats replaced at a dealership (yuck) in accordance with the recall.
the only symptom is that OCCASIONALLY the engine will hesitate a little bit when accelerating. Everything is pointing to O2 sensors being bad. Any advice?

1 Answer


Jimm

Jimm 1/17/2020

Please note that none of these DTC fault codes describe simply replacing one or more of the O2 sensors.

P2096 Post Catalyst Fuel Trim System Too Lean Bank 1 and P2098 Post Catalyst Fuel Trim System Too Lean Bank 2

The causes for these DTC may include:
Low fuel pressure caused by a clogged filter, failing fuel pump, failed fuel pressure regulator or clogged or leaking injectors.
Rough running engine due to misfiring plugs. Many engines have misfire codes to indicate the cylinder effected, such as P0307 for number 7.
A large vacuum leak would cause a massive amount of un-metered air to enter the intake manifold resulting in an overly lean mixture.
A large air leak at or near the number one oxygen sensor would also cause a lean mixture. A plugged converter will cause of host of driveability problems as well as set this code.
A severely plugged converter will result in the inability to increase rpm when under load. Look for a code such as P0421 -- catalytic converter efficiency below threshold if the converter indicating a faulty converter. A faulty oxygen sensor. This will set a code in itself, however, a faulty oxygen sensor does not automatically condemn the sensor. The code just means that the sensor signal was not within specifications.
An air leak or any of the above will cause an erroneous signal. There is a multitude of O2 codes relating to O2 performance which gives a clue to the problematic area. The Mass Airflow sensor will also cause this problem. It would be accompanied by a code such as P0100 -- Mass Airflow circuit malfunction. The Mass Airflow sensor is a hot wire that senses the volume of air entering the intake manifold. The computer uses this information to control fuel mixture.
Rusty exhaust systems, cracked exhaust manifolds or damaged or missing gaskets or donuts will cause air leaks.

P2196 = O2 Sensor Signal Biased/Stuck Rich (Bank 1 Sensor 1)
P2198 = O2 Sensor Signal Biased/Stuck Rich (Bank 2 Sensor 1)


Potential causes of a P2196 and P2198 code include:
Oxygen (O2) or A/F ratio sensor or sensor heater malfunction
Open or short in O2 sensor circuit (wiring, harness)
Fuel pressure or fuel injector problem
Faulty PCM Intake air or engine vacuum leaks
Faulty fuel injector(s) Fuel pressure too high or too low
PCV system leak/fault
A/F sensor relay faulty
MAF sensor malfunction
ECT sensor malfunction
Air intake restriction
Fuel pressure too high
Fuel pressure sensor malfunction
Fuel pressure regulator malfunction
Note on some vehicles that have been modified this code may be caused by the modifications (e.g. aftermarket exhaust, headers, etc.).

O2 sensor (downstream) = WALKER PRODUCTS part#25024692 - or it's equivalent

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