Intermittent Problem Diagnosis

WARNING: This page is about a different car, the 2002 Isuzu Trooper, 2002 Isuzu Rodeo Sport, 2002 Isuzu Rodeo, 2002 Isuzu Axiom, and 2002 Honda Passport. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: An intermittent problem may or may not illuminate the MIL or set a DTC. Unless directed there from a specific test DO NOT use DTC testing for intermittent problems. Fault must be present to locate problem.

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

Poor mating of connector halves or a terminal not fully seated in harness connector (terminal backed out).
Improperly formed or damaged terminal(s).
All connector terminals in suspect circuit should be carefully checked for proper contact tension.
Poor terminal-to-wire connection. Test this requires removing terminal from the harness connector body to test. Road test the vehicle with a DVOM connected to a suspected circuit. An abnormal voltage when malfunction occurs is a good indication that there is a fault in circuit being monitored. Use a Tech 2 or equivalent scan tool to help detect intermittent conditions.
The scan tool has several features that can be used to locate an intermittent condition. Using a Tech 2's FREEZE FRAME buffer or FAILURE RECORDS buffer can aid in locating an intermittent condition. Review and record information in FREEZE FRAME or FAILURE RECORD associated with intermittent DTC being diagnosed. Vehicle can be driven within the conditions that were present when DTC originally set. To check for loss of diagnostic code memory, disconnect MAP sensor and idle engine until MIL illuminates. DTC P0107 should be stored and kept in memory when ignition is turned off. If not, PCM is faulty. When this test is completed, clear DTC P0107 from memory.
An intermittent MIL with no stored DTC may be caused by following:
- Ignition coil shorted to ground and arcing.
- MIL signal circuit to PCM shorted to ground.
- Poor PCM grounds. See WIRING DIAGRAMS article. Check for improper installation of electrical options such as lights, cellular phones, etc. Check all wires from PCM to ignition coils for poor connections. Check for an open diode across A/C compressor clutch and check for other open diodes.
- Check Calibration ID of PCM, and compare it with the latest Isuzu service bulletins and/or Isuzu EEPROM reprogramming equipment to determine if an update to PCM's reprogrammable memory has been released. To check Calibration ID, connect scan tool to Data Link Connector (DLC). DLC is located under small cover on left side of instrument panel. On scan tool, select POWERTRAIN CONTROL MODULE, then select CALIBRATION ID. This identifies contents of the reprogrammable software and calibration contained in PCM. If CALIBRATION ID is not the most current available, it is advisable to reprogram PCM's EEPROM memory, which may either help identify a hard-to-find problem or may fix the problem. See EEPROM PROGRAMMING PROCEDURE under POWERTRAIN CONTROL MODULE in appropriate SELF-DIAGNOSTICS article.