Cat mfg guidance for P0420 issues

[simple_gifts]

http://download.deccats.com/POP/DEC_3_fold_brochure.pdf

This guide from DEC suggests using scantool to determine whether the ECM is correctly controlling the a/f mixture or if it is fluctuating because of other issues.

The !echo! is throwing a p0420 and i replaced the O2 sensors maybe 18 months ago?

At my mileage a new cat might be in order.

 

[dparm]

P0420 basically means the differential value between the pre- and post-cat O2 sensors is incorrect. Typically the post-cat sensor will read too close to the pre-cat sensor, indicating the exhaust gas isn't coming out very much cleaner. This means the cat has failed.

First step is to make sure both sensors are working. If the wires are long enough, try swapping them and see if the code returns. With the right scantool you might be able to read the values in case the wires aren't long enough.

If the sensors are good, the next step is to replace the cat converter.

 

[Chris142]

99% of the time a 420 code is a bad cat

 

[Merkava_4]

It's the back pressure you gotta watch out for. Anything over 2 psi back pressure is a plugged catalytic converter. It's a simple test. All you do is get a back pressure gauge that threads into your upstream oxygen sensor port. Even under full throttle, you shouldn't have more that 2 psi back pressure.