An intermittent condition may or may not turn on the malfunction indicator lamp
(MIL) or store a diagnostic trouble code (DTC).
Preliminary Inspection
Perform a visual inspection to locate the cause of the problem.
| • | The fault must be present to locate the problem. If a fault is intermittent,
the use of DTC tables may result in the replacement of good parts. |
Electrical Connections or Wiring
Poor electrical connections or wiring can cause most intermittent problems.
Perform a careful inspection of the suspected circuit for the following:
| • | Inspect for poor mating of the connector halves, or terminals not fully
seated in the connector body, backed-out. |
| • | Inspect for improperly formed or damaged terminals. Carefully reform or
replace all the connector terminals in the problem circuit to ensure the proper contact
tension. |
| • | Inspect for poor terminal to wire connections. This requires removing
the terminal from the connector body to inspect. |
Road Test
If a visual/physical inspection does not locate the cause of the problem, drive
the vehicle with a DMM connected to a suspected circuit or use a scan tool. An abnormal
voltage or scan reading, when the problem occurs, indicates the problem may be in
that circuit.
Intermittent Malfunction Indicator Lamp (MIL)
The following can cause an intermittent MIL and no DTCs:
| • | Electrical system interference caused by a malfunctioning relay, ECM driven
solenoid, or switch. The electrical component can cause a sharp electrical surge.
Normally, the problem will occur when the malfunctioning component is operating. |
| • | The improper installation of electrical devices; such as lights, 2-way
radios, electric motors, etc. |
| • | The MIL circuit intermittently shorted to ground. |
Loss of DTC Memory
Inspect for loss of DTC memory by disconnecting the engine coolant temperature
(ECT) sensor and idling the engine until the MIL turns ON. An ECT DTC should store
and remain in memory when turning OFF the ignition for at least 10 seconds.
If not, the ECM is malfunctioning.
Additional Inspection
Inspect for an open diode across the A/C compressor clutch and for other open
diodes.
