RAM SRT-10 Pickup V10-505 8.3L (2004)
Check Gauges Lamp: Description and Operation
A check gauges indicator is standard equipment on all instrument clusters. On vehicles equipped with a gasoline engine, the check gauges indicator is
located near the lower edge of the instrument cluster, between the tachometer and the speedometer. On vehicles equipped with a diesel engine, the check
gauges indicator is located on the left side of the instrument cluster, to the left of the voltage gauge.
The check gauges indicator consists of a stencil-like cutout of the words "CHECK GAGES" 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 "CHECK GAGES" text to appear in red through the translucent outer layer of the overlay when the
indicator is illuminated from behind by the LED, which is soldered onto the instrument cluster electronic circuit board. The check gauges indicator is
serviced as a unit with the instrument cluster.
The check gauges indicator gives an indication to the vehicle operator when certain instrument cluster gauge readings reflect 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) on vehicles equipped 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 check gauges 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 check gauges indicator for the following reasons:
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Bulb Test - Each time the ignition switch is turned to the On position the check gauges indicator is illuminated for about two seconds as a bulb
test.
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Engine Temperature High Message - Each time the cluster receives three consecutive bus messages from the PCM or ECM indicating the
engine coolant temperature of a gasoline engine is about 122° C (252° F) or higher, or of a diesel engine is about 112° C (233° F) or higher, the
check gauges indicator will be illuminated and a single chime is sounded. The indicator remains illuminated until the cluster receives a message
from the PCM or ECM indicating that the engine coolant temperature of a gasoline engine is below about 122° C (252° F), or of a diesel engine is
below about 112° C (233° F), or until the ignition switch is turned to the Off position, whichever occurs first.
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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 about 41 kPa (6 psi) or lower, the check gauges indicator will be illuminated and a single chime is sounded. The 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 indicator on in response to an engine oil
pressure low message if the engine speed is greater than zero.
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System Voltage Low (Charge Fail) Message - Each time the cluster receives three consecutive messages from the PCM or ECM indicating the
electrical system voltage is less than about 9.0 volts (charge fail condition) or that the battery temperature sensor input is an open circuit, the check
gauges indicator will be illuminated and a single chime is sounded. The indicator remains illuminated until the cluster receives a single message
from the PCM or ECM indicating the electrical system voltage is greater than about 9.5 volts (but less than about 15.5 volts), or until the ignition
switch is turned to the Off position, whichever occurs first.
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System Voltage High Message - Each time the cluster receives three consecutive messages from the PCM or ECM indicating the electrical
system voltage is greater than about 15.5 volts, the check gauges indicator will be illuminated and a single chime is sounded. The indicator
remains illuminated until the cluster receives a single message from the PCM or ECM indicating the electrical system voltage is less than about
15.0 volts (but greater than about 9.5 volts), or until the ignition switch is turned to the Off position, whichever occurs first.
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Actuator Test - Each time the cluster is put through the actuator test, the check gauges 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.
On vehicles with a gasoline engine, the PCM continually monitors the engine temperature, oil pressure, and electrical system voltage, then sends the
proper messages to the instrument cluster. On vehicles with a diesel engine, the ECM continually monitors the engine temperature, oil pressure, and
electrical system voltage, then sends the proper messages to the instrument cluster.
For proper diagnosis of the PCM, the ECM, the PCI data bus, or the electronic message inputs to the instrument cluster that control the check gauges
indicator, a diagnostic scan tool is required.
