Grand Cherokee 4WD Laredo V8-4.7L (2002)
Oil Pressure Gauge: Description and Operation
OIL PRESSURE GAUGE
An oil pressure gauge is standard equipment on all instrument clusters. The oil pressure gauge is located in the upper right corner of the instrument
cluster, to the right of the speedometer. The oil pressure gauge consists of a movable gauge needle or pointer controlled by the instrument cluster
circuitry and a fixed 90 degree scale on the gauge dial face that reads left-to-right from 0 - 5.4 kg/cm (metric cluster for gasoline engines), from 0 -
8.3 kg/cm (metric cluster for diesel engines), or from 0 - 80 psi (U.S. cluster), depending upon the market for which the vehicle is manufactured. An
International Control and Display Symbol icon for "Engine Oil" is located on the gauge dial face.
The oil pressure gauge graphics are either white, gray and orange against a black gauge dial face (base cluster) or black and gray against a taupe gauge
dial face (premium cluster), making them clearly visible within the instrument cluster in daylight. When illuminated from behind by the panel lamps
dimmer controlled cluster illumination lighting with the exterior lamps turned ON, the base cluster white gauge graphics appear blue-green and the
orange graphics still appear orange, while the premium cluster taupe gauge dial face appears blue-green with the black graphics silhouetted against the
illuminated background. The gray gauge graphics for both versions of the cluster are not illuminated. The orange gauge needle in the base cluster
gauge is internally illuminated, while the black gauge needle in the premium cluster gauge is not.
Base cluster gauge illumination is provided by replaceable incandescent bulb and bulb holder units located on the instrument cluster electronic circuit
board. Premium cluster gauge illumination is provided by an integral electro-luminescent lamp that is serviced as a unit with the instrument cluster.
The oil pressure gauge is serviced as a unit with the instrument cluster.
The oil pressure gauge gives an indication to the vehicle operator of the engine oil pressure. This gauge is controlled by the instrument cluster circuit
board based upon cluster programming and electronic messages received by the cluster from the Powertrain Control Module (PCM) over the
Programmable Communications Interface (PCI) data bus. The oil pressure gauge is an air core magnetic unit that receives battery current on the
instrument cluster electronic circuit board through the fused ignition switch output (RUN/START) circuit whenever the ignition switch is in the ON or
Start positions. The cluster is programmed to move the gauge needle back to the low end of the scale after the ignition switch is turned to the OFF
position. The instrument cluster circuitry controls the gauge needle position and provides the following features:
-
Engine Oil Pressure Normal Message - Each time the cluster receives a message from the PCM indicating the engine oil pressure is within the
normal operating range [above 0.28 kg/cm (above 4 psi), the gauge needle is moved to the relative pressure position of the gauge scale.
-
Engine Oil Pressure Low Message - Each time the cluster receives a message from the PCM indicating the engine oil pressure is about 0.28
kg/cm or lower (about 4 psi or lower), the gauge needle is moved to the far left (low) end of the gauge scale. The gauge needle remains at the low
end of the scale until the cluster receives a message from the PCM indicating that the engine oil pressure is about 0.56 kg/cm or higher (about 8
psi or higher).
-
Communication Error - If the cluster fails to receive an engine oil pressure message, it will hold the gauge needle at the last indication for about
twelve seconds or until a new engine oil pressure message is received, whichever occurs first. After twelve seconds, the cluster will return the
gauge needle to the low end of the gauge scale.
-
Actuator Test - Each time the cluster is put through the actuator test, the gauge needle will be swept across the entire gauge scale and back in
order to confirm the functionality of the gauge and the cluster control circuitry.
The PCM continually monitors the engine oil pressure sensor to determine the engine oil pressure. The PCM then sends the proper engine oil pressure
messages to the instrument cluster. For further diagnosis of the oil pressure gauge or the instrument cluster circuitry that controls the gauge, refer to
Instrument Cluster Diagnosis and Testing. If the instrument cluster turns ON the check gauges indicator due to a low oil pressure gauge reading, it
may indicate that the engine or the engine oiling system requires service. For proper diagnosis of the engine oil pressure sensor, the PCM, the PCI data
bus, or the electronic message inputs to the instrument cluster that control the oil pressure gauge, a DRB III scan tool is required Refer to the
appropriate diagnostic information.
