Dodge Ram Truck 1500-2500-3500. Manual — part 398

The odometer VFD is soldered onto the cluster electronic circuit board and is visible through a window with a
smoked clear lens located on the lower edge of the tachometer gauge dial face of the cluster overlay. The dark lens
over the VFD prevents the indicator from being clearly visible when it is not illuminated. The “LOW WASH” text
appears in an amber color and at the same lighting level as the odometer/trip odometer information when it is illu-
minated by the instrument cluster electronic circuit board. The washer fluid indicator is serviced as a unit with the
VFD in the instrument cluster.

OPERATION

The washer fluid indicator gives an indication to the vehicle operator that the fluid level in the washer reservoir is
low. This indicator is controlled by the instrument cluster circuit board based upon cluster programming and elec-
tronic messages received by the cluster from the Front Control Module (FCM) (also known as the Integrated Power
Module/IPM or Power Distribution Center/PDC) over the Programmable Communications Interface (PCI) data bus.

The washer fluid indicator 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 indicator only illuminates when it is switched to ground by the instrument cluster circuitry. The
instrument cluster will turn on the washer fluid indicator for the following reasons:

•

Washer Fluid Indicator Lamp-On Message - Each time the cluster receives a washer fluid indicator lamp-on
message from the FCM indicating that a low washer condition has been detected for sixty consecutive sec-
onds, the washer fluid indicator is illuminated and a single chime tone is sounded. The indicator remains illu-
minated until the cluster receives a washer fluid indicator lamp-off message for sixty consecutive seconds from
the FCM or until the ignition switch is turned to the Off position, whichever occurs first. The chime tone feature
will only repeat during the same ignition cycle if the washer fluid indicator is cycled off and then on again by
the appropriate washer fluid lamp messages from the FCM.

•

Actuator Test - Each time the cluster is put through the actuator test, the washer fluid indicator will be turned
on, then off again during the VFD portion of the test to confirm the functionality of the VFD and the cluster
control circuitry.

The FCM continually monitors the washer fluid level switch in the washer reservoir to determine the level of the
washer fluid. The FCM then sends the proper washer fluid indicator lamp-on and lamp-off messages to the instru-
ment cluster. For further diagnosis of the washer fluid indicator or the instrument cluster circuitry that controls the
indicator, (Refer to 8 - ELECTRICAL/INSTRUMENT CLUSTER - DIAGNOSIS AND TESTING).

For proper diagnosis of the washer fluid level switch, the FCM, the PCI data bus, or the electronic message inputs
to the instrument cluster that control the washer fluid indicator, a diagnostic scan tool is required. Refer to the appro-
priate diagnostic information.

WATER-IN-FUEL INDICATOR

DESCRIPTION

A water-in-fuel indicator is only found in the instrument
clusters for vehicles equipped with an optional diesel
engine. The water-in-fuel indicator is located near the
lower edge of the instrument cluster, between the
tachometer and the speedometer.

The water-in-fuel indicator consists of stencil-like cutout of the International Control and Display Symbol icon for
“Water In Fuel” 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 icon 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 water-in-fuel indicator is serviced as a unit with the instrument cluster.

OPERATION

The water-in-fuel indicator gives an indication to the vehicle operator when there is excessive water in the fuel sys-
tem. This indicator is controlled by a transistor on the instrument cluster circuit board based upon the cluster pro-

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INSTRUMENT CLUSTER -SERVICE INFORMATION

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gramming and electronic messages received by the cluster from the Engine Control Module (ECM) over the
Programmable Communications Interface (PCI) data bus.

The water-in-fuel 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 water-in-fuel indicator for the following reasons:

•

Bulb Test - Each time the ignition switch is turned to the On position the water-in-fuel indicator is illuminated
for about two seconds as a bulb test.

•

Water-In-Fuel Lamp-On Message - Each time the cluster receives a water-in-fuel lamp-on message from the
ECM indicating that there is excessive water in the diesel fuel system, the water-in-fuel indicator will be illu-
minated. The indicator remains illuminated until the cluster receives a water-in-fuel lamp-off message, or until
the ignition switch is turned to the Off position, whichever occurs first.

•

Actuator Test - Each time the cluster is put through the actuator test, the water-in-fuel 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 ECM continually monitors the water-in-fuel sensor to determine whether there is excessive water in the diesel
fuel system. The ECM then sends the proper water-in-fuel lamp-on and lamp-off messages to the instrument cluster.
For further diagnosis of the water-in-fuel indicator or the instrument cluster circuitry that controls the indicator, (Refer
to 8 - ELECTRICAL/INSTRUMENT CLUSTER - DIAGNOSIS AND TESTING).

For proper diagnosis of the water-in-fuel sensor, the ECM, the PCI data bus, or the electronic message inputs to the
instrument cluster that control the water-in-fuel indicator, a diagnostic scan tool is required. Refer to the appropriate
diagnostic information.

DR/DH

INSTRUMENT CLUSTER -SERVICE INFORMATION

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LAMPS

TABLE OF CONTENTS

page

LAMPS/LIGHTING - EXTERIOR - ELECTRICAL

DIAGNOSTICS . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

LAMPS/LIGHTING - EXTERIOR - SERVICE

INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . 107

LAMPS/LIGHTING - INTERIOR - ELECTRICAL

DIAGNOSTICS . . . . . . . . . . . . . . . . . . . . . . . . . 174