Symptom Diagnosis: Intermittents

Most intermittent problems are caused by faulty electrical connections or wiring. Perform a careful visual/physical check for the following conditions:

• Poor mating of the connector halves or a terminal not fully seated in the connector (backed out).
• Improperly formed or damaged terminal.
• All connector terminals in the problem circuit should be carefully checked for proper contact tension.
• Poor terminal-to-wire connection. This requires removing the terminal from the connector body to check.

Road test the vehicle with a J 39200 Digital Multimeter connected to a suspected circuit. An abnormal voltage when the malfunction occurs is a good indication that there is a fault in the circuit being monitored.

Use a Tech 2 to help detect intermittent conditions. The scan tool has several features that can be used to locate an intermittent condition. Use the following feature to find intermittent faults:

• Using a Tech 2"s "Freeze Frame" buffer or "Failure Records" buffer can aid in locating an intermittent condition. Review and record the information in the freeze frame or failure record associated with the intermittent DTC being diagnosed. The vehicle can be driven within the conditions that were present when the DTC originally set.

To check for loss of diagnostic code memory, disconnect the ECT sensor and idle the engine until the MIL (Check Engine lamp) comes on. DTC P0117 should be stored and kept in memory when the ignition is turned "OFF". If not, the ECM is faulty. When this test is completed, make sure that you clear the DTC P0117 from memory.

An intermittent MIL (Check Engine lamp) with no stored DTC may be caused by the following:

• Ignition coil shorted to ground and arcing.
• MIL (Check Engine lamp) wire to ECM shorted to ground.
• Poor ECM grounds. Refer to the ENGINE PERFORMANCE .

Check for improper installation of electrical options such as lights, cellular phones, etc. Check all wires from the ECM to the ignition coils for poor connections.

Check for an open diode across the A/C compressor clutch and check for other open diodes (refer to ENGINE PERFORMANCE .

If problem has not been found, refer to Visual/Physical Check  tables.

• Check the "Calibration ID" of the ECM, and compare it with the latest Isuzu service bulletins and/or Isuzu EEPROM reprogramming equipment to determine if an update to the ECM's reprogrammable memory has been released. To check the "Calibration ID", connect the Tech 2, then look for "Engine", then select "Calibration ID". This identifies the contents of the reprogrammable software and calibration contained in the ECM. If the "Calibration ID" is not the most current available, it is advisable to reprogram the ECM's EEPROM memory, which may either help identify a hard-to-find problem or may fix the problem.
• Calibration ID (example)