Question about 2004 Chevrolet Cavalier

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P0420P - 2004 Chevrolet Cavalier

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We are assumingn that you are talking about DTC P0420

P0420 OBD-II Trouble Code - Catalyst System Efficiency Below Threshold (Bank 1)

What does that mean? The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

Symptoms: You will likely not notice any drivability problems, although there may be symptoms.

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: Need a catalytic converter? Visit our catalytic converter shopping area for the lowest price on your replacement converter!

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
* Replace the catalytic converter

One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car 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.

Hope helps (remember rated this).

Posted on Jul 15, 2010

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I have a 2006 Pontiac Torrent showing codes P0171, P0420 and P0420P. Any help?


171 and 420 both have the same area that will cause these codes to pop..

you need either your O2 sensors replaced or new catalytic converter replace, if you have over 140,000 miles I would replace both ..

Jun 02, 2015 | 2006 Pontiac Torrent

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