Grand Cherokee 2WD V8-318 5.2L VIN Y MFI (1994)
Malfunction Indicator Lamp: Description and Operation
PURPOSE
The Malfunction Indicator Lamp is used to indicate immediate service of the engine control system is required.
The lamp will illuminate when the Powertrain Control Module (PCM) detects an open or shorted circuit, absence of current flow in an output
device, or if the oxygen sensors are not switching.
OPERATION
The Malfunction Indicator Lamp illuminates when the ignition key is turned to the ON position and stays lit for 3 seconds as a bulb test.
When the lamp is illuminates it indicates the PCM has entered limp in mode. When in limp in mode, the PCM substitutes the reading from a
functioning input for the failed input value.
Signals that can set Malfunction Indicator Lamp are battery voltage input, charging system, manifold Absolute Pressure sensor (MAP), Throttle
Position Sensor (TPS), coolant temperature sensor.
The Malfunction Indicator Lamp can also be used to display fault codes that have been stored in the PCM memory due to a system failure.
