An intermittent condition may or may not turn on the malfunction
indicator lamp (MIL) or store a diagnostic trouble code (DTC).
Preliminary Checks
Perform a visual check 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 check of the suspected circuit for the following:
| • | Check for poor mating of the connector halves, or terminals not
fully seated in the connector body, backed-out. |
| • | Check for improperly formed or damaged terminals. Carefully reform
or replace all the connector terminals in the problem circuit to ensure the
proper contact tension. |
| • | Check for poor terminal to wire connections. This requires removing
the terminal from the connector body to check. |
Road Test
If a visual/physical check 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
Check 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 Checks
Check for an open diode across the A/C compressor clutch and for other
open diodes.
