Diagnostic System Check

Circuit Description
Powertrain OBD system check is an organized approach to identifying a problem created by an electronic engine control system malfunction. The Powertrain OBD system check is the starting point for any driveability concern diagnosis, because it directs the service technician to the next logical step in diagnosing the concern. Understanding the table and using it correctly will reduce diagnostic time and prevent the replacement of good pans.DO NOT perform this check if a driveability concern is not present.

Diagnostic Aids
Inspect all related wiring and connections including the connections at the PCM. These may cause an intermittent malfunction. Check terminals for the following:
^ Damaged.
^ Corroded.
^ Pushed out terminals.

Test Description
The numbers below refer to the step numbers in the Diagnostic Table.
1. The Powertrain OBD system check should not be performed unless one of the concerns noted is present. Failure to follow this procedure could lead to misdiagnosis of the system.
2. The MIL should be on steady with the ignition ON and the engine OFF.
3. This step checks whether the PCM and the scan tool can communicate (serial data).
4. This step checks whether the vehicle will start.
5. Before proceeding to the applicable DTC table consider all of the items below.
^ Check for related service bulletins.
^ If multiple DTCs are stored, refer to the DTC tables using the following priority:
1. PCM error DTCs (P0601, P0603).
2. System voltage DTCs.
3. Component level DTCs (sensors, switches, relays, output drivers, etc.).
4. System level DTCs (Misfire, Fuel trim, HO2S lean or rich, etc.).
^ First failures of Type B DTCs will store in Last Test Failed, but not in History. When the MIL is on and a DTC is displayed in History, a current fault is indicated.
^ If the scan tool is unable to record DTC information, then record the DTC information on paper.
6. This step detects a MIL circuit shorted to ground.
7. Before proceeding to Symptoms or Components, check for related service bulletins. The diagnostic tables are designed for use with a properly functioning scan tool. If a faulty scan tool is suspected connect it to another vehicle to verify operation. Serial data communications must be corrected before beginning any other diagnostic procedure. OBD II serial data may not transmit if system voltage is below 9.0 volts or above 16.0 volts. DO NOT clear DTCs unless directed by a diagnostic procedure. Clearing DTCs also clears valuable Freeze Frame/Failure Record data. Testing and Inspection