Cherokee 4WD L6-4.0L VIN S (1998)
Temperature Warning Lamp/Indicator: Description and Operation
SYSTEM OPERATION
The coolant temperature warning lamp gives an indication when the engine coolant temperature is high. The lamp is turned on by the instrument
cluster circuitry for about three seconds after the ignition switch is turned to the On position as a bulb test. After the bulb test, the lamp is
controlled by the instrument cluster circuitry based upon an engine coolant temperature message received from the Powertrain Control Module
(PCM) on the Chrysler Collision Detection (CCD) data bus.
The PCM uses an input from the engine coolant temperature sensor and internal programming to decide what engine coolant temperature message
is required. The PCM then sends the proper message to the instrument cluster on the CCD data bus. If the PCM message indicates that coolant
temperature is high, the instrument cluster circuitry turns on the coolant temperature warning lamp and generates a single chime tone.
The engine coolant temperature sensor is installed in a threaded hole that penetrates a coolant passage of the engine. It is a thermistor-type sensor
that changes its internal resistance with changes in engine coolant temperature.
