RAM 2500 Truck 4WD V8-5.7L VIN D (2005)
Oil Pressure Gauge: Description and Operation
An oil pressure gauge is standard equipment on all instrument clusters. The oil pressure gauge is located in the upper right quadrant of the instrument
cluster, above the coolant temperature gauge.
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
cluster overlay that reads left-to-right from "L" (or Low) to "H" (or High) for gasoline engines except SRT-10. On SRT-10 models, the scale reads from
"0" kPa to "700" kPa in markets where a metric instrument cluster is specified, or from "0" psi to "100" psi in all other markets. On vehicles with a
diesel engine the scale reads from "0" kPa to "760" kPa in markets where a metric instrument cluster is specified, or from "0" psi to "110" psi in all
other markets.
An International Control and Display Symbol icon for "Engine Oil" is located on the cluster overlay, directly below the left end of the gauge scale. On
all models except SRT-10 the oil pressure gauge graphics are black against a white field except for two red graduations at the low end of the gauge scale.
On SRT-10 the gauge graphics are black against a silver field except for a single red zone at the low end of the gauge scale. In either case, the gauge
graphics are 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 black graphics
appear blue-green and the red graphics still appear red. The gauge needle has internal optical illumination. Gauge illumination is provided by replaceable
incandescent bulb and holder units located on the instrument cluster electronic circuit board. 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) on vehicles with a
gasoline engine, or from the Engine Control Module (ECM) on vehicles equipped with a diesel engine 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:
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Engine Oil Pressure Message - The instrument cluster circuitry restricts the oil pressure gauge needle operation in order to provide readings that
are consistent with customer expectations. For all models except SRT-10, each time the cluster receives a message from the PCM or ECM
indicating the engine oil pressure is above about 41 kPa (6 psi) the cluster holds the gauge needle at a point near the middle increment within the
normal range on the gauge scale. For SRT-10 models, each time the cluster receives a message from the PCM indicating the engine oil pressure is
above about 41 kPa (6 psi) the cluster moves the gauge needle in a linear fashion to the proper relative pressure position of the gauge scale.
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Engine Oil Pressure Low Message - Each time the cluster receives three consecutive bus messages from the PCM or ECM indicating the engine
oil pressure is below about 41 kPa (6 psi), the gauge needle is moved to the red graduations (except SRT-10) or to the red zone (SRT-10) at the
far left end of the gauge scale, the check gauges indicator is illuminated, and a single chime tone is generated. The gauge needle remains at the left
end of the gauge scale and the check gauges indicator remains illuminated until the cluster receives a message from the PCM or ECM indicating
that the engine oil pressure is above about 41 kPa (6 psi), or until the ignition switch is turned to the Off position, whichever occurs first. The
cluster will only turn the check gauges indicator on in response to an engine oil pressure low message if the engine speed message is greater than
zero.
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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
ten seconds, or until the ignition switch is turned to the Off position, whichever occurs first. After ten seconds, the cluster will move the gauge
needle to the low end of the gauge scale.
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Actuator Test - Each time the cluster is put through the actuator test, the oil pressure gauge needle will be swept to several calibration points on
the gauge scale in a prescribed sequence in order to confirm the functionality of the gauge and the cluster control circuitry.
On vehicles with a gasoline engine, the PCM continually monitors the engine oil pressure sensor to determine the engine oil pressure. On vehicles with a
diesel engine, the ECM continually monitors the engine oil pressure sensor to determine the engine oil pressure. The PCM or ECM then sends the proper
engine oil pressure messages to the instrument cluster. 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 ECM, the PCI data bus, or the electronic message inputs to the instrument cluster
that control the oil pressure gauge, a diagnostic scan tool is required.
