W T E C I I I E L E C T R O N I C C O N T R O L S T R O U B L E S H O O T I N G M A N U A L
Intermittent codes are a result of faults that are detected, logged, and then disappear, only to recur later. If, when
troubleshooting, a code is cleared in anticipation of it recurring and it does not, check the items in the following list
for the faults source.
1. Intermittent power/ground problems can cause voltage problems during ECU diagnostic checks
which can set various codes depending upon where the ECU was in the diagnostic process.
2. Damaged terminals.
3. Dirty or corroded terminals.
4. Terminals not fully seated in the connector. Check indicated wires by uncoupling connector and
gently pulling on the wire at the rear of the connector and checking for excessive terminal move-
5. Connectors not fully mated. Check for missing or damaged locktabs.
6. Screws or other sharp pointed objects pushed into or through one of the harnesses.
7. Harnesses which have rubbed through and may be allowing intermittent electrical contact between
two wires or between wires and vehicle frame members.
8. Broken wires within the braiding and insulation.
Finding an Intermittent Fault Condition
To find a fault, like one of those listed, examine all connectors and the external wiring harnesses. Harness
routing may make it difficult to see or feel the complete harness. However, it is important to thoroughly
check each harness for chafed or damaged areas. Road vibrations and bumps can damage a poorly installed
harness by moving it against sharp edges and cause some of the faults. If a visual inspection does not
identify a cause, move and wiggle the harness by hand until the fault is duplicated.
The next most probable cause of an intermittent code is an electronic part exposed to excessive vibration,
heat, or moisture. Examples of this are:
1. Exposed harness wires subjected to moisture.
2. A defective connector seal allows moisture to enter the connector or part.
3. An electronic part (ECU, shift selector, solenoid, or throttle sensor) affected by vibration, heat, or
moisture may cause abnormal electrical conditions within the part.
When troubleshooting Item 3, eliminate all other possible causes before replacing any parts.
Another cause of intermittent codes is good parts in an abnormal environment. The abnormal environment
will usually include excessive heat, moisture, or voltage. For example, an ECU that receives excessive
voltage will generate a diagnostic code as it senses high voltage in a circuit. The code may not be repeated
consistently because different circuits may have this condition on each check. The last step in finding an
intermittent code is to observe if the code is set during sudden changes in the operating environment.
Troubleshooting an intermittent code requires looking for common conditions that are present whenever
the code is diagnosed.
APPENDIX A IDENTIFICATION OF POTENTIAL CIRCUIT PROBLEMS