Grand Cherokee 2WD V6-3.7L (2008)
Oil Pressure Warning Lamp/Indicator: Description and Operation
Low Oil Pressure Indicator
A low oil pressure indicator is standard equipment on all instrument clusters. This indicator is located above the coolant temperature gauge and to the
right of the tachometer in the cluster overlay.
The low oil pressure indicator consists of a stencil-like cutout of the International Control and Display Symbol icon for Engine Oil 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. A red
Light Emitting Diode (LED) behind the cutout in the opaque layer of the overlay causes the indicator to appear in red through the translucent outer layer
of the overlay when it is illuminated from behind by the LED, which is soldered onto the instrument cluster electronic circuit board.
The low oil pressure indicator is serviced as a unit with the instrument cluster.
The low oil pressure indicator gives an indication to the vehicle operator when the engine oil pressure reading reflects a condition requiring immediate
attention. 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 Powertrain Control Module (PCM) over the Controller Area Network (CAN) data bus.
The low oil pressure indicator Light Emitting Diode (LED) 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
LED will always be OFF when the ignition switch is in any position except ON or START. The LED only illuminates when it is provided a path to
ground by the instrument cluster transistor. The instrument cluster will turn ON the low oil pressure indicator for the following reasons:
Engine Oil Pressure Low Message - Each time the cluster receives an electronic engine oil pressure message from the PCM indicating the
pressure is about 6.9 kPa (1 psi) or lower, the low oil pressure indicator will be illuminated. The indicator can be flashed ON and OFF, or
illuminated solid, as dictated by the PCM message. The indicator remains illuminated solid or flashing until the cluster receives a message from
the PCM indicating that the pressure is above about 6.9 kPa (1 psi), or until the ignition switch is turned to the OFF position, whichever occurs
first. The cluster will only turn the indicator ON in response to low engine oil pressure if the engine speed is greater than zero.
Actuator Test - Each time the cluster is put through the actuator test, the low oil pressure indicator will be turned ON, then OFF again during the
bulb check portion of the test to confirm the functionality of the LED 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 messages to the
ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN). If the EMIC turns ON the indicator after the bulb test,
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 EMIC, the CAN data bus or the electronic communication related to low oil
pressure indicator operation a diagnostic scan tool is required. Refer to the appropriate diagnostic information.