Scan Tool Data List: Overview

Engine Scan Tool Data List
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. Some special considerations to keep in mind while making the OBD system check are:

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

Cold Oxygen Sensor (02S 1)
On certain engines, the Oxygen Sensor (O2S 1) may cool down after only a short period of operation at idle. This will cause the system to go into Open Loop. To restore Closed Loop operation, run the engine at part throttle several minutes and accelerate from idle to part throttle a few times.

Notice: A scan tool that displays faulty data should not be used and the problem should be reported to the manufacturer. The use of a faulty scan tool can result in misdiagnosis and unnecessary parts replacement.

Only the parameters listed below are used in this manual for diagnosis. If a scan tool reads other parameters, the values are not recommended by General Motors for use in diagnosis. For more description on the values and use of the scan tool to diagnose PCM inputs, refer to the applicable diagnostic section. If all values are within the ranges illustrated, refer to Symptoms.

TEST CONDITIONS
At Idle / Upper Radiator Hot / Closed Throttle / Transmission in Park or Neutral/ Closed Loop / Accessories Off.