- Preliminary Inspection

PRECAUTIONS IN IDENTIFYING DIAGNOSTIC TROUBLE CODES (DTCs)

- Do not disconnect connectors from the Engine Control Module (ECM), battery cables, ECM ground wire harness, or the 15 amp "TAIL DOME" Fuse. Such disconnection will erase ECM DTCs in memory.
- Note DTC indicated first.
- Intermittent malfunctions - There are cases where the scan tool indicates a DTC representing a fault which occurred only temporarily and has gone away. In such a case, it may occur that good parts are replaced unnecessarily. To prevent such an error, be sure to follow instructions given below when checking by using the "Diagnostic Tables."
- When a malfunction can be identified, that is, it is not an intermittent one, check the following areas:

- sensor
- wires
- each connection.

- When a fault cannot be identified, but the scan tool indicates a DTC:

- Diagnose the fault by using the appropriate DTC charts. If the sensor (actuator), wires and connections are all in good condition, erase the DTC from the ECM memory. Then conduct a test run and check what DTCs are present when the MIL illuminates. Only when it indicates a DTC again, is the fault present.

NOTES ON SYSTEM CIRCUIT INSPECTION

- Most intermittent malfunctions are caused by faulty electrical connections or wiring. Perform a careful check of suspect circuits for:

- Poor mating of connector halves, or terminals not fully seated into the connector body (backed out).
- Improperly formed or damaged terminals. All connector terminals in malfunctioning circuits should be carefully reformed to increase contact tension.
- Poor terminal to wire connection.

- Never connect any tester (voltmeter, ohmmeter, etc.) to the Engine Control Module (ECM) when the connectors are disconnected. Attempting to do so may cause damage to the ECM.
- Be sure to use a digital Multimeter whose minimum resistance is more than one Megohm per volt. Any other digital multimeter should not be used because accurate measurements are not obtained. (Use J 39200 or equivalent.)
- When checking voltage at each terminal of the connector which is connected to the ECM, be sure to connect the negative (-) probe to body ground and, using a jumper wire connect the positive (+) probe to connector terminal being tested. Applying the probes of digital Multimeter improperly may cause a sensor or the ECM to be shorted and damaged.