Thread: Service engine light

Originally Posted by buck

I think I'll start small with a tune up, even though the guy at the Zone said I didn't need one. It has 103 K miles and original plugs.

2003 Grand Prix GT Limited Edition.

I think thats a good start.

Would this be the ever so popular P0420?


Causes

A code P0420 may mean that one or more of the following has happened:

• Leaded fuel was used where unleaded was called for
• An oxygen sensor is not reading (functioning) properly
• The engine coolant temperature sensor is not working properly
• Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
• Retarded spark timing
• The oxygen sensors in front and behind the converter are reporting too similar of readings

Possible Solutions

Some suggested steps for troubleshooting a P0420 error code include:

• Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
• Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
• Inspect the downstream heated oxygen sensor (HO2), replace if necessary

Originally Posted by buck

It just dawned on me that about a week ago my son ran out of gas in the car. He used a gas can that use to mix two cycle engine oil in. It had about a gallon of 50/50 mix. Then I filled the tank later. My thought is that mabeye the oil gas mix screwed up the 02 sensor. (making the car think there was an oil leak inside the engine). any thoughts?

You run your 2 cycles 1 to 1??? Go through plugs much?

Has your cat been replaced? If an aftermarket converter was used, it may be the problem. I know of several people that have had issues with the P0420 code after a new cat was installed, they simply do not do a good enough job and the code is thrown.

it's really not good on the cat but one gallon shouldn't really hurt anything i wouldn't think.

Tune out the code

I have a high flow cat, and the code was removed. You can just let it be until you do the pulley drop and tune.