The ECU doesn't check cat temp. It only checks the oxygen level coming out of the cat. It expects to see a fairly steady reading. If the cat isn't working or isn't heating up, the downside oxygen sensor reading will be all over the place. See this post on what the Po420 or P0430 means: https://ricksfreeautorepairadvice.com/p0420-is-it-the-catalytic-converter-or-the-oxygen-sensor/
Buick Century 2001, 100,000 miles.....the code indicated thermostat issue. Cars engine is not heating up properly I guess. Check engine light is on, can't reset it with pushing Gas pedal 3 times. ...
2001 Buick Century Custom Sedan FWD
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Maintenance & Repair
CAT CONVERT WAS NOT HEATING UP TO SPECS.WOULNT THAT SET A CODE?
2001 Buick Century Custom Sedan FWD
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Maintenance & Repair
That's why service engine light and my service vehicle light come on on my 2001 Buick Century because the traction is off and the light is on also any lock brake light on
2001 Buick Century Custom Sedan FWD
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Maintenance & Repair
I just got my car the other day. It runs great, but every so often, when I turn it on, the service engine soon light pops up and the brake locks. If I switch gears it just slowly rolls as if in neut...
2001 Buick Century Custom Sedan FWD
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Maintenance & Repair
1996 Buick Century very rough cold start idle. I have to pump the gas to keep it from stalling; and the car automatically revs to keep the engine from stalling. "Check engine" light stays on . I'v...
1996 Buick Century Sedan FWD
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Maintenance & Repair
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