05-26-2009, 09:17 PM
Join Date: Apr 2009
Location: Orange County, CA
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 temperature sensor is not working properly
- Damaged or leaking / catalytic converter / exhaust pipe
- Retarded spark timing
- The oxygen sensors in front and behind the converter are reporting too similar of readings
Some suggested steps for troubleshooting a P0420 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
- Replace the catalytic converter
One thing to note is that many offer a longer warranty on emissions-related parts. So if you have a newer but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into.