For 1990-2009 cars

The Powertrain Control Module (PCM) is equipped with a self diagnostic feature that detects system failures and aids the technician in locating a faulty circuit. The PCM has memory for comparing various input information to programmed information. These conditions are described on the support page for each Diagnostic Trouble Code (DTC). If a value is not within the PCM parameters, a DTC will set and the default values or actions will be used, if applicable.

The PCM continually performs a self diagnostic check. You can use a scan tool in order to request the PCM to display any stored DTC.

Important: You cannot flash the DTC by grounding the DLC. Refer to Strategy Based Diagnosis in General Information, before beginning any diagnosis.

Important: Always refer to the Powertrain On-Board Diagnosis (OBD) System Check before diagnosing any DTC.

The scan tool displays all stored DTCs and Freeze Frame or Failure Records in current and history status. If the DTC is in history status, the condition may be intermittent. An intermittent DTC is one which will not reset during the current ignition cycle. The support page of a DTC contains Diagnostic Aids to help locate intermittent conditions.

For more information on PCM operation and DTC modes, refer to the Engine Controls Section.

When diagnosing specific DTCs, always diagnose and repair the first DTC set. After you have made the repair and the DTC is cleared, road test the vehicle and check for DTCs to reset. A failed component or circuit often causes other related components and circuits to display faulty information or to set a false DTC.

Each DTC has a specific diagnostic table and support page. The diagnostic table contains a series of tests that pinpoint a specific failure. The support page contains a circuit description, a list of enable conditions that must be met to set the code, a Diagnostic Aids section to help locate intermittent conditions, and a test description section that identifies specific steps in the DTC table. The table and the support page were designed to be used together so that you will better understand the circuit and the diagnostic procedure.

If a visual check does not locate the cause of the fault, test the suspected circuit with a J 39200 Digital Multimeter (DMM). Use the J 39200 DMM to check for the following opens and shorts:

• | Short to voltage -- Connect the J 39200 DMM, set on the DC voltage scale, to a known good ground.

• | Short to ground -- Connect the J 39200 DMM, set on the DC voltage scale, to a known good battery voltage.

• | Open circuit -- Connect the J 39200 DMM, set on the ohms scale, to each end of the circuit with voltage removed from the circuit.

For complete electrical test descriptions and procedures, refer to Circuit Testing in Wiring Repairs.

### Intermittent and Performance Diagnostic Trouble Codes

The DTC tables in this section determine if there is a fault within the circuit. The fault must be present in order to locate the problem. If an intermittent condition occurs, a DTC is stored in history status, but a check of the circuit will indicate a normal condition. When diagnosing intermittent trouble codes, thoroughly check the suspected circuit for the following conditions:

• | Poor terminal tension

• | Poor setting of the connector halves

• | Poor connections between the terminal and the wire

• | Improperly formed or damaged terminals

• | Faulty PCM power or ground connections

• | Electrical system surges which are caused by a defective relay, solenoid, or switch. Normally these conditions occur when the faulty component is operated.

• | Electromagnetic Interference (EMI)