P0420 Catalyst System Low Efficiency

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P0420 in a Prius

EDIT #2: I rescanned, looking at the correct data, and found the rear O2 sensor was definitely bouncing up and down with the forward sensor's lambda reading. Since I have looked for leaks and ...
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1answer
25 views

Error Codes Related to Transmission?

2002 Ford Mustang V6 My car started having a new problem yesterday. When I drive down the road randomly the pedal loses rpm's. For instance I'll be going 40mph and then there is no resistance on the ...
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3answers
2k views

06 Chevy Cobalt ls 2.2 l . Replaced B1S1 O2 sensor still having issues

I went and had my 06 Cobalt checked out because the dreeded check engine light came one and I got the P0420 threshold bank 1 code. My mechanic, who has been a good friend of mine for quite some time, ...
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1answer
86 views

P0420 code for 09 Murano

I've had several opinions stating my car needs a cat converter but after failing inspection today, the mechanic said it might need ECT sensor changed. I've read previous posts that cat converters ...
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1answer
464 views

Faulty TCC solenoid or bad computer?

Make: Pontiac Model: Sunfire Year: 2001 Engine: 2.2 L Trans: Automatic Hello to every one, bought my first car and it is fine except for this little annoying problem. After driving it for a ...
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3answers
35k views

Check Engine code P0420 Catalyst efficiency below threshold bank 1

After months of normal driving with no problems, my 2003 Honda Civic EX check engine light came on during a long trip. Got it scanned and it's P0420: Catalyst efficiency below threshold bank 1. They ...
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3answers
13k views

What would cause a car to lose power a few seconds after starting, then run normally?

I start my 2003 Honda Civic each morning and drive to work. A few hundred feet down the road, the engine will sometimes behave as though it is running out of gas and lose power momentarily. It ...
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2answers
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2005 Dodge Ram: easy way to diagnose code P0420?

My truck is reporting a code P0420, which apparently is "Catalyst System Efficiency Below Threshold (Bank 1)" which can either be the catalytic converter or the rear O2 sensor. The code came on at ...