Grand Cherokee 2WD V8-4.7L VIN J (2004)
Coolant Level Indicator Lamp: Description and Operation
COOLANT LOW INDICATOR
A coolant low indicator is only found in the instrument clusters of vehicles equipped with an optional diesel engine. The coolant low indicator should
not be confused with the coolant level low indication provided by the Electronic Vehicle Information Center (EVIC) of vehicles equipped with a
gasoline engine, although they do perform the same function. The coolant low indicator is located in the lower left corner of the instrument cluster, to
the left of the tachometer. The coolant low indicator consists of an International Control and Display Symbol icon for "Low Coolant" imprinted on an
amber lens. The lens is located behind a cutout in the opaque layer of the instrument cluster overlay. The dark outer layer of the overlay prevents the
indicator from being clearly visible when it is not illuminated. The icon appears silhouetted against an amber field through the translucent outer layer
of the overlay when the indicator is illuminated from behind by a replaceable incandescent bulb and bulb holder unit located on the instrument cluster
electronic circuit board. When the exterior lighting is turned ON, the illumination intensity of the coolant low indicator is dimmable, which is adjusted
using the panel lamps dimmer control ring on the control stalk of the left multi-function switch. The coolant low indicator lens is serviced as a unit
with the instrument cluster lens, hood and mask unit.
The coolant low indicator gives an indication to the vehicle operator when the diesel engine coolant level is low. This indicator is controlled by a
transistor on the instrument cluster circuit board based upon cluster programming and electronic messages received by the cluster from the Body
Control Module (BCM) over the Programmable Communications Interface (PCI) data bus. The coolant low indicator bulb is completely controlled
by the instrument cluster logic circuit, and that logic will only allow this indicator to operate when the instrument cluster receives a battery current
input on the fused ignition switch output (RUN/START) circuit. Therefore, the indicator will always be OFF when the ignition switch is in any
position except ON or Start. The bulb only illuminates when it is provided a path to ground by the instrument cluster transistor. The instrument cluster
will turn ON the coolant low indicator for the following reasons:
-
Bulb Test - Each time the ignition switch is turned to the ON position the coolant low indicator is illuminated for about three seconds as a bulb
test.
-
Coolant Low Indicator lamp-ON Message - Each time the cluster receives a coolant low indicator lamp-ON message from the BCM indicating
the engine coolant is below the minimum level in the coolant reservoir, the coolant low indicator will be illuminated. The indicator remains
illuminated until the cluster receives a coolant low indicator lamp-OFF message from the BCM indicating that the engine coolant level is above the
minimum level.
-
Actuator Test - Each time the cluster is put through the actuator test, the coolant low indicator will be turned ON for the duration of the test to
confirm the functionality of the bulb and the cluster control circuitry.
The BCM continually monitors the input from the coolant level switch, then sends the proper coolant low indicator lamp-ON and lamp-OFF messages
to the instrument cluster. If the coolant low indicator fails to light during the bulb test, replace the bulb with a known good unit. For further diagnosis
of the coolant low indicator or the instrument cluster circuitry that controls the indicator, refer to Instrument Cluster Diagnosis and Testing. For proper
diagnosis of the coolant level switch, the BCM, the PCI data bus, or the electronic message inputs to the instrument cluster that control the coolant low
indicator, a DRB III scan tool is required. Refer to the appropriate diagnostic information.
