Intermittent Check Engine Light

There are cases where "CHECK ENGINE" light indicates a diagnostic code representing a trouble which occurred only temporarily and has gone. In such case, it may occur that good parts are replaced unnecessarily. To prevent such an accident, be sure to follow instructions given below when checking by using "FLOW OF DIAGNOSIS".

^ When trouble can be identified, that is, it is not an intermittent one:
Check sensor (actuator), wires and each connection and if they are all in good condition, substitute a known-good ECM and recheck.

^ When trouble can not be identified but "CHECK ENGINE" light indicates a trouble code:
Diagnose trouble by using that code No. and if sensor (actuator), wires and each connection are all in good condition, erase diagnostic code in ECM memory. Then conduct a test run and check what "CHECK ENGINE" light indicates. Only when it indicates trouble code again, substitute a known-good ECM and check again.
If it indicates not trouble code but normal code No. 12, it means that an intermittent trouble did occur and has gone. In this case, check wires and connections carefully again.