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 and 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,
PCM driven solenoid or switch. They 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 malfunction indicator lamp (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 engine coolant
temperature (ECT) DTC should store and remain in memory when turning
OFF the ignition for at least 10 seconds. If not, the PCM is malfunctioning.
Additional Checks
Check for an open diode across the A/C compressor clutch and for other
open diodes.
