Scan Tool Testing and Procedures: Overview

The Powertrain OBD System Check is an organized approach to identifying a problem created by an electronic engine control system malfunction. The OBD system check is the starting point for any driveability complaint diagnosis. This directs the service technician to the next logical step in diagnosing the complaint. Keep the following special considerations in mind while making the OBD system check:

Blocking Drive Wheels
The vehicle drive wheels should always be blocked and the emergency brake set while checking the system.

Cold Oxygen Sensor (O2S 1)
On certain engines, the Oxygen Sensor (O2S 1) may cool down after only a short period of operation at idle. This may cause the system to go into an Open Loop operation. Run the engine at part throttle several minutes and accelerate the engine from idle to part throttle a few times in order to restore a Closed Loop operation.

NOTICE: Do not use a scan tool that displays faulty data. Report the scan tool problem to the manufacturer. Use of a faulty scan tool can result in misdiagnosis and unnecessary parts replacement.

Only the parameters listed are used for diagnosis. If a scan tool reads other parameters, General Motors does not recommend these values for use in the diagnosis. If all of the values are within the illustrated ranges, refer to Symptoms.