Dreaded p0420
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Dreaded p0420 I have been doing some work for a family member on his 2008 Avalanche with a 6.0, he has a P0420, I put in a set of aftermarket converters and nothing changed, (tried to keep it cheap but kicked me in the ***) Finally installed a set of factory converters from GM with new O2 sensors, The light stayed off for a while but returned with a P0420. also did new spark plugs as well. I did end up updating the ECU with the latest and greatest software too. (I work at a Chevrolet dealership) Not sure what is going on but seeing if there is something I am missing.
Did you change both O2 sensors? (The code is generated by comparing the readings from the two on either side of the converter.)
If you have changed both, I would start looking at the other causes that can cause issues with the catalytic system efficiency:
If you have changed both, I would start looking at the other causes that can cause issues with the catalytic system efficiency:
- Damaged muffler or leaks in the muffler.
- Damaged exhaust manifold or leaks in the exhaust manifold.
- Damaged exhaust pipe or exhaust pipe leaks.
- A misfire in the engine.
- Oil contamination in catalytic converter.
- Faulty engine coolant temperature sensor.
- A leaking fuel injector.
- High fuel pressure.
Excellent response....
Did you change both O2 sensors? (The code is generated by comparing the readings from the two on either side of the converter.)
If you have changed both, I would start looking at the other causes that can cause issues with the catalytic system efficiency:
If you have changed both, I would start looking at the other causes that can cause issues with the catalytic system efficiency:
- Damaged muffler or leaks in the muffler.
- Damaged exhaust manifold or leaks in the exhaust manifold.
- Damaged exhaust pipe or exhaust pipe leaks.
- A misfire in the engine.
- Oil contamination in catalytic converter.
- Faulty engine coolant temperature sensor.
- A leaking fuel injector.
- High fuel pressure.
I should have also mentioned, that if a K&N or other oiled air filter is involved with the vehicle, it would probably be best/safest to toss that also.
GM has warned about the oil shedding and coating O2 sensors (although most of us have had more experience with MAF contamination). If the air filter oil can make it through the engine, it could get to the CAT. (Still unlikely that it would do so in such a volume to cause a problem with the CAT, more likely the O2's.)
GM has warned about the oil shedding and coating O2 sensors (although most of us have had more experience with MAF contamination). If the air filter oil can make it through the engine, it could get to the CAT. (Still unlikely that it would do so in such a volume to cause a problem with the CAT, more likely the O2's.)
