Dodge ram truck 3500 1996 Service Manual page 418

8E - 4 INSTRUMENT PANEL SYSTEMS B R
D E S C R I P T I O N A N D O P E R A T I O N (Continued)
GEAR SELECTOR INDICATOR
The gear selector indicator gives an indication of
the position of the automatic transmission gear selec­
tor lever. The indicator is mounted to the instrument
cluster housing.
The indicator is mechanically actuated by a cable
connected to the PRNDL driver of the gear selector
lever mechanism on the steering column. This group
covers only the removal and Installation of the gear
selector indicator. Refer to Group 21 - Transmission
for the diagnosis and adjustment of this component.
OIL PRESSURE GAUGE
The oil pressure gauge gives an indication of the
engine oil pressure. The combination oil pressure
switch/sending unit contains a flexible diaphragm
and a variable resistor coil. The diaphragm moves in
response to changes in the engine oil pressure. The
sending unit is installed in a threaded hole that pen­
etrates a oil passage of the engine. As the diaphragm
moves, resistance in the coil increases or decreases.
High resistance on the gauge side of the sending unit
causes low oil pressure readings. Low resistance
causes high oil pressure readings. Sending unit resis­
tance values are shown in a chart in Specifications at
the back of this group.
SPEEDOMETER/ODOMETER
The speedometer/odometer gives an indication of
the current vehicle speed, and displays a cumulative
total of the distance the vehicle has traveled. The
speedometer/odometer unit receives a vehicle speed
pulse signal from the Vehicle Speed Sensor (VSS). An
electronic integrated circuit contained within the
speedometer/odometer unit reads and analyzes the
pulse signal. I t then adjusts the ground path resis­
tance of one electromagnet in the gauge to control
speedometer needle movement. I t also sends signals
to an electric stepper motor to control movement of
the odometer number rolls. The frequency values for
the pulse signal are shown in a chart in Specifica­
tions at the back of this group.
The VSS is mounted to an adapter near the trans­
mission (two-wheel drive) or transfer case (four-wheel
drive) output shaft. The sensor is driven through the
adapter by a speedometer pinion gear. The adapter
and pinion used may vary with transmission and
transfer case models, axle ratio and tire size. Refer to
Group 21 - Transmission for more information.
TACHOMETER
The tachometer gives an indication of the engine
speed in revolutions-per-minute (rpm). With the
engine running, the tachometer receives an engine
speed pulse signal from the powertrain control mod­
ule. An electronic integrated circuit contained within
the tachometer unit reads and analyzes this pulse
signal. I t then adjusts the ground path resistance for
one of the electromagnets in the gauge to control
gauge needle movement. The frequency values for
the pulse signal are shown in a chart in Specifica­
tions at the back of this group.
TRIP ODOMETER
Like the odometer, the trip odometer gives an indi­
cation of the distance the vehicle has travelled. How­
ever, by depressing the trip odometer reset knob on
the face of the speedometer/odometer unit, the trip
odometer number rolls can be reset to zero. The trip
odometer is driven by the same signal and circuits as
the speedometer and odometer. The trip odometer is
serviced only as a part of the speedometer/odometer
gauge unit.
VOLTMETER
The voltmeter gives an indication of the vehicle's
electrical system voltage. The voltmeter is connected
in parallel with the battery. With the ignition switch
in the On position, the voltmeter indicates the bat­
tery voltage or the generator output voltage, which­
ever is greater.
AIRBAG INDICATOR L A i P
The airbag indicator lamp lights for 6 to 8 seconds
each time the ignition switch is turned to the On
position as a bulb test, and to indicate that a system
self-test is in progress. The lamp is switched to
ground by the Airbag Control Module (ACM). I f the
lamp remains on after the self-test, or comes on
while driving, i t may indicate that the ACM has
detected a system malfunction and/or that the airbag
system has become inoperative. Refer to Group 8 M -
Passive Restraint Systems for more information.
ANTI-LOCK BRAKE SYSTEM LAMP
R E A R WHEEL
ANTI-LOCK
On vehicles equipped with the standard Rear
Wheel Anti-Lock (RWAL) brake system, the Anti-
Lock Brake System (ABS) lamp is switched to ground
by the RWAL control module. The RWAL control
module lights the lamp when the ignition switch is
turned to the Start position as a bulb test. The lamp
will stay on for 3 to 5 seconds after vehicle start-up
to indicate that a system self-test is in progress. I f
the lamp remains on after start-up, or comes on and
stays on while driving, it may indicate that the
RWAL control module has detected a system mal­
function and/or that the RWAL system has become
inoperative. Refer to Group 5 - Brakes for more infor­
mation.