Malfunction Indicator Lamp: Description and Operation

OPERATION
Self Test
As a functional test, the malfunction indicator lamp (MIL) illuminates at key-on before engine cranking.

Trouble Code Set Operation
Whenever the Powertrain Control Module (PCM) sets a diagnostic trouble code that effects vehicle emissions, it illuminates the MIL.
- The PCM illuminates the MIL only for diagnostic trouble codes that effect vehicle emissions.
- The MIL remains on until the diagnostic trouble code is erased.
- When the ignition switch is turned OFF, the lamp goes out.
- Even if the ignition switch is turned ON again, the lamp does not come on until the irregularity is detected.
- After that, if the PCM does not re-detect the malfunction for 51 drives, the diagnostic trouble code will be erased from the PCM memory.

ITEMS INDICATED BY THE CHECK ENGINE/MALFUNCTION INDICATOR LAMP
- No cam signal at PCM MAP sensor voltage too high
- Front bank O2S stays above center (rich) Slow change in idle MAP sensor signal
- Front bank O2S stays below center (lean) EGR system failure
- Rear bank O2S stays above center (rich) Intake air temperature sensor voltage low
- Rear bank O2S stays below center (lean) Intake air temperature sensor voltage high
- EGR solenoid circuit Injector #4 control circuit
- EVAP purge solenoid circuit Front bank O2S shorted to voltage
- Injector #3 control circuit Rear bank O2S stays at center
- Injector #2 control circuit Rear bank O2S shorted to voltage
- Injector #1 control circuit Injector #5 control circuit
- Idle air control motor circuit Injector #6 control circuit
- Throttle position sensor voltage low Battery temperature sensor volts out of limit
- Throttle position sensor voltage high Low speed fan control relay circuit
- Engine coolant temperature sensor voltage too low Fuel pump relay control circuit
- Engine coolant temperature sensor voltage too high No 5 volts to MAP sensor
- Front bank HO2S stays at center No 5 volts to throttle position sensor
- No vehicle speed sensor signal Intermittent loss of camshaft position or crankshaft position
- MAP sensor voltage too low Speed control switch always high

CAUTION: If the check engine/malfunction indicator lamp illuminates because of a malfunction of the PCM, transmission between the scan tool and the PCM cannot occur. In this case, the diagnostic trouble code cannot be read.