Dear All,,

How can I fix this problem:

p0420: catalyst system efficiency below threshold bank 1

 

Replace the catalytic converter.

 

Do you mean change catalytic completely ?

 

If there are no other problems, Replace. How many miles on it?

"Some suggested steps for troubleshooting and fixing a P0420 error code include:
Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady). Inspect the downstream heated oxygen sensor, replace if necessary
Replace the catalytic converter"

Read more at: https://www.obd-codes.com/p0420

 

92000 km

 

I replaced my cats but with magnaflo cats and new O2 sensors and still have the code.
The O2 sensors don't like the after market cats and I wasn't about to pay the GM price and 30 day wait to get them.
Now to come up with a fix for the after market cats throwing codes on my Alpha.

 

One easy way to do it is to get the truck tuned. They can turn the rear O2 sensors off. If you live in a state that tests emissions, may not be an option for you though.

That's what I did, no cats here.

 

Thanks, I'll have to check into that since we don't have emissions testing here in Florida.

 

Did you clear the code after replacing the Cats? Did you use ACDelco O2 sensors?

 

yes to both. It comes back next time the engine is started each time. Will stay off until then too.