P0420 code

CLEVASH

MEMBER
2002 CHEVROLET BLAZER
117,640 MILES

Obd 11 scanner keeps coming up with p0420 code, something keeps triggering the check engine light to come on and have no ides what. Changed spark plugs& wires, replaced front o2 sensor and replaced cat converter. Checked for vac leaks and found none also checked for any oil leaking anywhere and found nothing. What else could be wrong

5 Replies

BILLYMAC

MECHANIC
2,204 POSTS

This is a cataliyst code triggered by bad oxygen sensor

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Wednesday, February 22nd, 2012 AT 3:19 AM

CLEVASH

MEMBER
3 POSTS

So which one would it be? I replaced the front o2 sensor. So is it the rear one

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Wednesday, February 22nd, 2012 AT 3:28 AM

BILLYMAC

MECHANIC
2,204 POSTS

I would think it must be the rear. Could possibly be restricted convertor I would have it checked at exhaust shop. This code is not specifically for the 02 sensor rather insufficient flow in the exhaust. So you really need to eliminate the possibility of a bad convertor first.

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Wednesday, February 22nd, 2012 AT 3:31 AM

CLEVASH

MEMBER
3 POSTS

So is taking it to a shop the only way to find out if its the converter? Which should I try first? Replacing the rear o2 sensor or having the converter looked at?

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Wednesday, February 22nd, 2012 AT 3:39 AM

BILLYMAC

MECHANIC
2,204 POSTS

Yes the only acurate way not expensive they drill a hole in it and attach a backpressure guage take a reading. Yes you can always just buy a sensor and try that atleast you will know. We never replace any sensor without a hard code for that sensor then we test the parameters of the sensor 'but we have to sell it to the customer so we have to know it is bad. But new sensors are always good to have