This bulletin applies to 2002-2018 Chevy Escalade, Avalanche, Express, Silverado, Tahoe and Suburban models, Cadillac Escalade, Hummer H and GMC Savana, Sierra and Yukon models.
The SES light may be experienced on vehicles that have recently been serviced by replacing a catalytic converter. 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:
1. 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 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 may have occurred. 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 to set.
2. If the DTCs set shortly after the catalytic converter has been replaced, it may be a result of the engine run time restrictions to no longer be 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 drive cycle below.
In order to achieve proper catalytic converter temperature and allow the mat material to out-gas (break-in), perform the following drive cycle:
1. Drive the vehicle at sustained highway speed for 25 to 30 minutes.
2. Bring the vehicle to a stop.
3. Shut off the engine for 1 minute.
4. Restart the engine and resume highway speed for an additional 10 to 15 minutes.
5. Bring the vehicle to a stop.
6. Shut the engine off for 1 minute.
7. Restart the engine and operate the vehicle at the conditions for running the DTC P0420/P0430 tests and assure that the vehicle passes these diagnostic tests.