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.

STORED DTCs
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 10 seconds or longer. DTCs 16, 43 and 51 however, are exceptions to this statement and are not stored in the ECM's memory once a fault is no longer detected.

ENTERING DIAGNOSTIC MODE
A test diagnostic mode is incorporated within the ECM's diagnostics to help when diagnosing intermittent failures. To enter the test diagnostic mode, the test diagnostic mode terminal "TE2" of the Data Link Connector must be grounded. This terminal must be grounded with the ignition switch in the "LOCK" position before the ECM will enter the test diagnostic mode. By grounding this terminal, the threshold at which DTCs will set is lowered. The technician can then test drive the vehicle at the condition in which the malfunction originally occurred. After the test drive, diagnostic request terminal (TE1) can be grounded to determine which, if any, DTCs were set. If no DTCs were set with the ECM in the test diagnostic mode, refer to Powertrain Management / Computers and Control Systems / System Diagnosis / Diagnosis By Symptom for further intermittent failure diagnosis. A physical inspection of the applicable subsystem most often will resolve the malfunction.

DIAGNOSTIC CHARTS
If a malfunction is intermittent, do not use a Diagnostic Trouble Code chart.