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04-25-2010, 10:29 PM
Trouble code: P0420 Catalyst system efficiency below threshold (Bank1)
What dose that mean? How do I fix it? Desperate for answers,PLEASE

04-26-2010, 05:43 PM
Hi 007,

P0420 means the catalytic converter in the exhaust system connected to the no. 1 cylinder bank (the cylinder bank that contains cylinder no. 1) is not operating as well as it should. The PCM compares the upstream and downstream oxygen sensor signals; when operating normally (when the engine is fully warmed-up), the upstream sensor output voltage should be fluctuating rapidly, and the downstream sensor's output voltage should be more stable, indicating that the converter is doing its job. Most of the time a code P0420 means the converter is bad. There are some cases where a service bulletin has been released, instructing technicians to "re-flash" the PCM to make it so the threshold isn't quite as sensitive. This is worth looking into, because if that can be done and it fixes the problem, it's a lot cheaper than replacing a converter.
Also, before replacing a converter, you should make sure that there are no existing conditions that could destroy the new converter, such as misfiring or an out-of-range fuel trim. You can learn more bout this in Haynes Techbook no. 10206, OBD-II and Electronic Engine Management Systems.

I hope this helps.