Thread: new engine or parts for rebuilding

When you run headers and a hi-flow CAT or no CAT the code P0420 is thrown. You need to have the code removed. Removing the rear O2 sensor and installing a sim. will solve this problem but it creates another. GM installed a rear O2 diagnostic program on '01 and later model years. Basically, it checks to make sure that a rear O2 sensor is installed by increasing the fuel ratio then waiting for the proper signal from the rear O2 sensor. By running a simulator, the signal never changes and the diagnostic continues to run, and your engine continues to run super rich. Over time, this can lead to wash down and even bearing failure.

Chris..don't you mean when you remove a cat from our cars... headers won't actually set a code, a lack of a cat or lack of a good cat do that.

Originally Posted by BillBoost37

Chris..don't you mean when you remove a cat from our cars... headers won't actually set a code, a lack of a cat or lack of a good cat do that.

Corrected. Thanx Bill.

Can I make another correction? Its 01+ cars.

thought it was '00...corrected...thanx Cam