The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
A SES light may be experienced on low mileage vehicles, or vehicles that have recently had thecatalytic converter replaced.
Upon inspection, DTCs P0420 and/or P0430 may be stored.
On a new vehicle, catalytic converter efficiency DTCs P0420 and P0430 are disabled for the first hourof 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 onthe 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 beenachieved. 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 drive cycle below.
If the DTCs set shortly after the catalytic converter is replaced, it may be a result of the engine runtime restrictions no longer being in place since the vehicle is no longer new. As a result, the catalyticconverter may not have completed a thorough break-in cycle after replacement, possibly resulting ina 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 and suggestions:
Drive vehicle at sustained highway speed for 25 to 30 minutes
Bring vehicle to a stop
Shut off the engine for 1 minute
Restart the engine and resume highway speed for an additional 10 to 15 minutes
Bring vehicle to a stop
Shut off engine for 1 minute
Restart the engine and operate vehicle at the conditions for running the DTC P0420/430 tests andassure that the vehicle passes these diagnostic tests.
If the diagnostics for DTC P0420 and P0430 have passed, return the vehicle to customer forevaluation.
If the diagnostics do not pass, perform SI diagnostics and repair as necessary.
For vehicles repaired under warranty, please use the appropriate warranty labor operation based onthe actual cause and repair
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.
GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.