Malfunction Indicator Lamp: Testing and Inspection

INTERMITTENT MALFUNCTION INDICATOR LAMP
In the case of an intermittent malfunction, the Malfunction Indicator Lamp (MIL) will remain lit as long as the trouble exists and will go out when the system returns to normal, except in the case of Exhaust Gas Recirculation (EGR) intermittents. EGR intermittents will cause the MIL to remain lit until the ignition switch is turned to "LOCK."

DTCs STORED IN MEMORY
Even though the MIL goes out, the corresponding Diagnostic Trouble Code (DTC) will be stored in the memory of the Engine Control Module (ECM) unless system voltage is removed for 20 seconds or longer. DTC 41 (Ignition Signal Circuit), however, is an exception to this statement and is not stored in the memory of the ECM. For retrieval of an active DTC 41, refer to Computers and Control Systems / System Diagnosis / Procedures / Vehicle On Board Diagnostics. Testing and Inspection

UNEXPECTED DTCs
When unexpected DTCs appear during the DTC reading process, the assumption can be made that these DTCs were set by an intermittent malfunction and could be helpful in diagnosing the system.

INTERMITTENT DTCs
An intermittent DTC may or may not reset. If it is an intermittent failure, a Diagnostic Trouble Code Chart is not used. Consult the "Diagnostic Aids" heading contained within the diagnostic chart corresponding to the intermittent DTC. The topic of Intermittents is also covered in Diagnosis By Symptom. Refer to Powertrain Management / Computer and Control Systems / System Diagnosis. Testing and Inspection

PHYSICAL INSPECTION
A physical inspection of the applicable subsystem most often will resolve the malfunction.