Engine Controls - Trouble Shooting - No Codes: INTERMITTENTS

NOTE: The problem may or may not illuminate Malfunction Indicator Lamp (MIL) or store a Diagnostic Trouble Code (DTC). Do not use DTC tables for intermittent problems. The fault must be present to locate problem. Most intermittent problems are caused by faulty electrical connections or wiring. Perform a careful visual/physical check. Check for following conditions:

Poor mating of connector halves or a terminal not fully seated in connector.
Improperly formed or damaged terminal.
All connector terminals in problem circuit should be carefully checked for proper contact tension.
Poor terminal-to-wire connection. This requires removing terminal from connector body to check.
The vehicle may be driven with a Digital VoHmeter (DVM) connected to suspected circuit. An abnormal voltage when a malfunction occurs is a good indication that there is a fault in circuit being monitored.

A scan tool can be used to help detect intermittent conditions.

Using a scan tool's Freeze Frame buffer can aid in locating an intermittent condition. Review and record information in freeze frame associated with intermittent DTC being diagnosed. The vehicle can be driven within conditions that were present when DTC originally set.

To check loss of DTC memory, disconnect Throttle Position (TP) sensor and idle engine until MIL comes ON. DTC P0122 should be stored in memory and kept in memory when ignition is turned OFF. If not, powertrain control module (PCM)/engine control module (ECM) is faulty. When this test is completed, make sure that you clear DTC from memory.

An intermittent MIL with no stored DTC may be caused by following:
- Ignition coil shorted to ground and arcing at ignition wires or plugs.
- MIL wire to PCM/ECM shorted to ground.
- Poor PCM/ECM grounds.
  Check for an electrical system interference caused by a defective relay, PCM/ECM driven solenoid, or switch. They can caused a sharp electrical surge. Normally problem will occur when faulty component is operated. Check for improper installation of electrical options such as lights, cellular phones, etc. Check for open diode across A/C compressor clutch and check for other open diodes.