Chrysler RAM TRUCK 2500 1994 Service Manual page 400

• INSTRUMENT PANEL AND GAUIES 8E - 3
rent flow will change the magnetic field which
changes the pointer position.
A hinged float arm i n the fuel tank raises or lowers
depending on the fuel level. The float arm contacts a
variable resistor i n the gauge sending unit. This pro­
vides a change of resistance i n the fuel gauge circuit
with any up or down movement of the float. As the
resistance changes, the current changes and the
pointer moves to a new position (calibration values
shown in Specifications chart).
Sending unit resistance is high when the fuel level
in the tank is low and the float arm drops. Sending
unit resistance is low when the tank is full and the
float arm is raised.
SPEEDOMETER/ODOMETER
The speedometer/odometer system consists of an
electric speedometer/odometer and pushbutton reset
trip odometer mounted i n the cluster. The system
also includes the wire harness from the cluster to the
vehicle speed sensor at the transmission, and the
adapter and pinion i n the transmission. The electric
speedometer/odometer has the same appearance as a
mechanical version, but i t eliminates the drive cable.
A signal is sent from a transmission mounted vehicle
speed sensor to the speedometer/odometer circuitry
through the w r i n g harness. Refer to Group 21 -
Transmission for selecting the proper pinion, and se­
lecting and indexing the proper adapter.
TACHOMETER
The tachometer displays the engine speed (RPM).
With the engine running, the tachometer receives an
engine speed signal from the PCM pin 43 (calibration
values shown i n Specifications chart).
WARNING LAMPS
LOW OIL PRESSURE
The oil pressure warning switch, mounted on the
engine, is controlled by engine oil pressure. The lamp
should only light when the engine is first started.
When engine oil pressure is normal, the switch is
held i n the off or open position. This stops current
from flowing to the low oil pressure warning lamp on
the instrument panel.
When the engine oil pressure is low, the switch is
in the on or closed position. This allows current to
flow to the low oil pressure warning lamp i n the in­
strument cluster causing the warning lamp to illumi­
nate.
FOUR-WHEEL DRIVE INDICATOR
Indicates that the transfer case is i n a four-wheel
drive mode of operation.
MALFUNCTION INDICATOR (CHECK ENGINE)
LAMP
The malfunction indicator (Check Engine) lamp i l ­
luminates each time the ignition switch is turned
ON. I t will stay on for 3 seconds as a bulb test.
I f the PCM receives an incorrect signal or no signal
from certain sensors or emission related systems, the
lamp is turned on (pin 32 of PCM). This is a warning
that the PCM has recorded a system or sensor mal­
function. I n some cases, when a malfunction of a
monitored circuit occurs, the PCM will go into a
limp-in mode of operation i n an attempt to keep the
system operating (except diesel). I t signals an imme­
diate need for service.
The lamp can also be used to display diagnostic
trouble codes (DTC). Cycle the ignition switch ON-
OFF-ON-OFF-ON within 3 seconds. This will allow
any DTC's stored in the PCM to be displayed i n a se­
ries of flashes representing digits. Refer to Group 14
- General Diagnosis Sections for a listing of the
codes.
AIRRAG WARNING
This lamp monitors the airbag system. This lamp
will come on when the ignition switch is turned to
the ON position and should stay l i t for 6 to 8 sec­
onds.
I f the a i r b a g w a r n i n g l a m p e i t h e r fails t o
l i g h t , o r goes o n a n d stays on, there is a system
malfunction. Refer t o the a p p r o p r i a t e Diagnos­
tic Test Procedures m a n u a l t o diagnose the
p r o b l e m .
S E A T B E L T REMINDER
This lamp is illuminated i f the ignition switch is
ON and the driver's seat belt is not buckled. The
lamp will go off after 4 to 8 seconds.
For testing of this system refer to Group 8U -
Chime/Buzzer Warning Systems.
MAINTENANCE REQUIRED—HDC S.9L V8/8.0L
V - 1 0
This system is designed to act as a reminder that
scheduled vehicle emissions maintenance must be
performed, as required by federal emissions laws. I t
is n o t i n t e n d e d to indicate a w a r n i n g o r t h a t a
state o f emergency exists w h i c h m u s t be cor­
rected t o insure safe vehicle operation. When
the lamp has been activated, certain service/mainte­
nance must be performed. For required service/main­
tenance, stated in time or mileage, refer to Group 0 -
Lubrication and Maintenance. Also refer to Group 25
- Emission Control System for information.
UPSHIFT INDICATOR
Vehicles equipped with manual transmissions have
an upshift indicator lamp. The lamp is controlled by
the PCM. The lamp illuminates to indicate when the