- Intermittent Malfunctions

NOTE: When an intermittent problem occurs the "Service Engine Soon" light may not be illuminated and a will not necessarily store a code. Also, it is important to note that diagnosis of these problems should not be performed with Trouble Code Charts. Use of these charts can result in good parts being replaced.

CONDITION I
Most intermittent problems are caused by faulty wiring and/or poor electriccal connections, and any affected circuit should be thoroughly inspected for such. If visual inspection does not reveal a cause for the problem proceed as follows:
1. Connect a voltmeter or Scan tool to the affected circuit.
2. While driving the vehicle any irregular voltage reading may indicate the problem is in that circuit.
3. If further inspection of the affected circuit reveals the connectors and wiring are good, and a Trouble Code (except Codes 44 and 45) was stored for a sensor circuit, substitute the affected sensor with a known good sensor then recheck that circuit.

CONDITION II
To Check for a loss of trouble code memory, ground the dwell lead for at least 10 seconds with the "test" lead left ungrounded. A code 23 should be stored after the engine is stopped and the ignition is turned to "run". If this is not achieved the ECM is faulty.

CONDITION III
An intermittent "Service Engine Soon" light with no Trouble Code set may be caused by a sharp electrical surge in a faulty relay, ECM driven solenoid, or switch. This will most likely occur when the component is operational. To diagnose this condition, inspect the following
1. Proper installation of all optional electrical equipment.
2. Ensure EST wires are routed away from the alternator, ignition components and wires, and spark plug wires. Ensure the ECM ignition system wire has a good ground.
3. Check that the ignition secondary is not shorted to ground.
4. Check the "Service Engine Soon" and "Diagnostic Test" leads for an intermittent short to ground.
5. Check all ECM grounds.