P0420 Catalyst System Low Efficiency - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 11-02-2005, 11:46 AM   #1
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Default P0420 Catalyst System Low Efficiency

(PO420) has anybody had that code come up before? if so what did you do to fix it?
thanks for any help you can give.
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Old 11-02-2005, 12:12 PM   #2
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That'* going to be either a rear O2 sensor failure (emissions only, no performance loss) or a bad catalytic converter. The cat can cause a loss in performance due to restriction and higher operating temps. How'* your WOT response?

Also be warned as a Cat comes apart, it can send nasty debris into your resonator and muffler.
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Old 11-03-2005, 12:01 AM   #3
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Majority of the time, that code signals a failed cat.
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Old 11-28-2005, 06:31 AM   #4
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still having problem. I think I will replace the CAT.
Any idea what one to buy and how much it will cost???
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Old 11-28-2005, 09:49 AM   #5
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Long as you are doing it.. look up the universal magnaflow hi flow cat with 2.5 inlet and outlet. Ebay usually has them for about $60 I hear.
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Old 11-28-2005, 01:23 PM   #6
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Are any other codes present?

According to the 97 FSM, things to check for code P0420 are as follows:

1. Inspect wiring harness at PCM for damaged, backed out terminals and poor terminal and wire connections.

2. Inspect cat for dents, severe discoloration, holes, internal rattle

3. Inspect Exhaust system (from rear exhaust flange manifold to cat) for leaks, damage, or loose/missing hardware.

4. Inspect Rear Oxygen (H02S 2) sensor (right behind the cat) to insure the sensor is mounted securely, and that the electrical pig-tail and wiring is connected and is not contacting the exhaust pipe or damaged. Also check the connector at the end of the pig-tail for loose/broken connectors.
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