Malfunction Indicator Lamp: Description and Operation

FUNCTION

The Check Engine Light is used to indicate immediate service of the engine control system is required. The lamp will illuminate when the Engine Controller detects an open or shorted circuit, absence of current flow in an output device, or if the oxygen sensors are not switching.


OPERATION

The Check Engine Light illuminates when the ignition key is turned to the ON position and stays lit for 3 seconds as a bulb test.

When the light is illuminated it indicates the Engine Controller has entered limp in mode. When in limp in mode, the Engine Controller substitutes a failed input value with a reading from another functioning input.

Signals that can set Check Engine Light are battery voltage input, charging system, manifold Absolute Pressure sensor (MAP), throttle Position Sensor (TPS), coolant temperature sensor.

The Check Engine Light can also be used to display fault codes that have been stored in the Engine Controller memory due to a system failure. To display codes with the Check Engine Light, see Powertrain Management/Computers and Control Systems/Testing and Inspection/Procedures.