A Code 13 stored in the ECM memory may be caused by an inoperative oxygen sensor. The oxygen sensor may not generate enough voltage to the ECM, or there may be an opening in the sensor wire which can cause the Check Engine light or Service Engine Soon Light on later models to come on and store Code 13.
If using the Code 13 diagnostic chart leads to the conclusion that the problem is intermittent, the Oxygen Sensor should be changed using the new sensor part number 8990741.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those 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 a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.