- Intermittent Malfunctions

SYMPTOM DESCRIPTION:
The SERVICE LAMPS come on at times, but do not stay on. There may or may not be a stored code.


NOTE: If an affected circuit is one that may be checked by the status lights, the switch tests, the output cycling tests, or engine data displays, make the check on the appropriate circuit. Some of the trouble codes include a "Note On Intermittents", in the text describing a suggested procedure for isolating the location of intermittent malfunctions.



FAULTY ELECTRICAL CONNECTIONS OR WIRING

Most intermittent problems are caused by faulty electrical connections or wiring. Perform a careful visual check of suspected circuits for:
^ Poor mating of the connector halves, or terminals not fully seated in the
connector body (backed out).
^ Improperly formed or damaged terminals. All connector terminals in
problem circuit should be carefully reformed or replaced to insure proper
contact tension.
^ Poor terminal to wire connection. This requires removing the terminal
from the connector body to check.



ROAD TEST

If a visual/physical check does not find the cause of the problem, the vehicle can be driven while using parameters or with a voltmeter connected to a suspected circuit. An abnormal voltage reading, when the problem occurs, indicates the problem may be in that circuit. If the wiring and connectors checkout OK, and a trouble code was stored for a circuit having a sensor, except for Codes E44 or EO44 and E45 or EO45, replace sensor.

NOTE: It would be advantageous to make note of any codes stored and clear the ECM/BCM memory prior to road testing. This may eliminate any false codes not related to the complaint.




INTERMITTENT "SERVICE ENGINE SOON (SES) LIGHT"

An intermittent "SES" light, and No Diagnostic Codes, could be caused by:
^ Electrical system interference caused by a defective relay, ECM driven
solenoid, or switch. These components can cause a sharp electrical surge.
Normally the problem will occur when the faulty component is operated.
^ Improper installation of electrical devices, such as lights, 2-way radios,
electric motors....etc.
^ EST wires should be routed away from spark plug wires, ignition system
components and generator. Circuit from ECM to ignition
system should have a good ground.
^ Ignition secondary shorted to ground.
^ SERVICE ENGINE SOON light or diagnostic "test"
terminal intermittently shorted to ground.
^ ECM/BCM grounds.



LOSS OF DIAGNOSTIC CODE MEMORY

To check, disconnect TPS and idle engine until SERVICE ENGINE SOON light comes "ON," Code E22 or EO22 should be stored, and kept in memory when the ignition is turned "OFF" for at least 10 seconds. If not, the ECM is faulty.