Grand Cherokee 2WD L6-4.0L VIN S (1997)
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 four 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 message received from the Body Control Module
(BCM) on the Chrysler Collision Detection (CCD) data bus.
The BCM uses a fuel level message received from the Powertrain Control Module (PCM) on the CCD data bus to decide when the fuel level is
low. The BCM then sends the proper message to the instrument cluster on the CCD data bus to turn the lamp on or off. when the lamp-on message
is sent, the BCM also issues a single low fuel warning chime tone. Once the lamp is turned on, an increase in the fuel level of at least one-half
gallon is required before the PCM input to the BCM will change and cause a lamp-off message to be issued. If the PCM detects a short or open in
the fuel gauge sending unit circuit, it sends a message on the CCD data bus that will cause the fuel gauge pointer to move to the empty stop and the
low fuel lamp to be turned on.
