GM Catalytic Converter Break

A service engine soon light may be experienced on low-mileage vehicles, or vehicles that have recently had the catalytic converter replaced and DTCs P0420 and/or P0430 may be stored.

On a new vehicle, catalytic converter efficiency DTCs P0420 and P0430 are disabled for the first hour of engine run-time to allow break-in of the catalytic converter.

The following scenarios may allow a DTC P0420 or P0430 to set after this hour of engine run-time has expired. If these DTCs are found on a new/low mileage vehicle, use the Tech 2 to verify engine run-time on the Engine Hour Meter in the IPC Data Display/Data 1 List. If the engine run-time is less than one hour, the battery may have been disconnected, or another vehicle power loss event may have occurred, during vehicle manufacturing.

This may allow the catalyst efficiency diagnostics to run before one hour of engine run-time has been achieved. If this occurs, the catalytic converter may not have completed a thorough break-in cycle, causing a false DTC P0420 and/or P0430 to set.

If this occurs, clear the DTCs and perform the following drive cycle. If the DTCs set shortly after the catalytic converter is replaced, it may be a result of the engine run-time restrictions no longer being in place since the vehicle is no longer new. As a result, the catalytic converter may not have completed a thorough break-in cycle after replacement, possibly resulting in a false DTC P0420 and/or P0430. If this occurs, clear the DTCs and perform the following drive cycle.

In order to achieve proper catalytic converter temperature and allow the mat material to out-gas (break-in), perform the following drive cycle and suggestions:

If the diagnostics for P0420 and P0430 have passed, return the vehicle to the customer. If the diagnostics do not pass, perform further diagnostics and repairs.