Cherokee 2WD L6-4.0L VIN S (1998)
Low Fuel Lamp/Indicator: Description and Operation
SYSTEM OPERATION
The low fuel warning lamp gives an indication when the fuel level in the fuel tank has fallen below about one-eighth of a full tank, as registered on
the fuel gauge. The instrument cluster circuitry lights the lamp for about three seconds when the ignition switch is turned to the On position as a
bulb test. After the bulb test, the instrument cluster circuitry controls the lamp based upon a fuel level message received from the Powertrain
Control Module (PCM) on the Chrysler Collision Detection (CCD) data bus.
The PCM uses an input from the fuel gauge sending unit and internal programming to decide what fuel level 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 the fuel level is below one-eighth of a
full tank for more than ten seconds, the instrument cluster circuitry turns on the low fuel warning lamp and generates a single chime tone. Once the
lamp is turned on, an increase in the fuel level message of at least one full needle width for more than twenty seconds is required before the cluster
will turn the lamp off.
The fuel gauge sending unit is mounted to the electric fuel pump module inside the fuel tank. The sending unit has a float attached to the end of a
swing-arm. The float moves up or down within the fuel tank as the fuel level changes. As the float moves, an electrical contact on the pivot end of
the swing-arm wipes across a resistor coil, which changes the resistance of the sending unit.
