P0420 Just threw that code, bad cat?
P0420 Just threw that code, bad cat? Well I just threw a P0420 code on my 00 WS6. I am the original owner and I have only 20k miles on the car. Assuming I double check first if its the 02 sensor, do you think the dealer will replace the cat if its bad? I have borla y-pipe and exhaust done but thats it. How should I approach them if I bring the car in for service, cause I dont want to pay to swap oxygen sensors if its the cat!
That code is for a insufficient catalyst. If the stock cat is bad it still should be covered under the emission warranty up to at least 50K.
Many times with headers its not unusual to get that code.
Many times with headers its not unusual to get that code.
No headers here just borla y-pipe and exhaust, I dont want to go to the dealer and have them pull some crap that its the oxygen sensor and pay for that then find out later to get the same code.
TECH Senior Member
Joined: Dec 2001
Posts: 5,399
Likes: 3
From: Jacksonville, FL
You could swap your rear 02's side to side and see if the code changes to P0430. Don't think they'll hassle you for your exhaust as long as they can bolt in a new cat. I know a couple people that had their's replaced free w/catbacks. Over the phone they got the "Might be an 02, have to charge a diagnostic fee, etc." but once they condemned the cat there was no charge.
Originally Posted by 2001NBMZ28
You could swap your rear 02's side to side and see if the code changes to P0430. Don't think they'll hassle you for your exhaust as long as they can bolt in a new cat. I know a couple people that had their's replaced free w/catbacks. Over the phone they got the "Might be an 02, have to charge a diagnostic fee, etc." but once they condemned the cat there was no charge.
If it changes to P0430 does that mean its the oxygen sensor?
TECH Senior Member
Joined: Dec 2001
Posts: 5,399
Likes: 3
From: Jacksonville, FL
Yep, clear any codes after the swap. If you get P0420 again should be the cat. Personally I wouldn't bother swapping them, it's most likely the cat - just something you can do to make sure it's not the sensor.
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Joined: Nov 2003
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From: Wichita KS / Rancho San Diego
Originally Posted by 2001NBMZ28
Yep, clear any codes after the swap. If you get P0420 again should be the cat. Personally I wouldn't bother swapping them, it's most likely the cat - just something you can do to make sure it's not the sensor.
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TECH Enthusiast
Joined: Jul 2006
Posts: 638
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From: San Diego
Bad O2 sensor won't cause code to move side to side. The code sets because the computer sees too much activity after the cat, ie. the front and rear O2 sensors are switching at the same rate. If the sensor is bad it will set a differant code.
My Silverado started throwing that code. At 120k miles, I put on Dynatech headers and hi flow cats. At 200k miles that code started popping up on gas I bought in Alabama and Texas. Now at 211k miles, that code comes up on gas in Georgia as well. I don't feel like buying cats, so I'm just going to tune out the ses for that code.
