Chrysler RAM TRUCK 2500 1994 Service Manual page 405

8E - 8 INSTRUMENT PANEL AND GAUGES •
? J948E-57
Fig. 4 Fuel Gauge Terminals—Low Line Cluster
COMBINATION OIL PRESSURE SENDING UNIT
The combination oil pressure sending unit has 2
functions:
(1) Lamp function. The sending unit provides a low-
resistance that keeps the low oil pressure warning
lamp on until there is oil pressure.
(2) Gauge function. The sending unit provides a re­
sistance that varies with oil pressure for gauge oper­
ation.
COMBINATION SENDING UNIT LAMP FUNCTION TEST
To test the combination oil pressure sending unit
lamp function, unplug the connector. Measure the re­
sistance between the sending unit switch terminal
(Fig. 5 ) and the metal housing (Figs. 6, 7 and 8). The
ohmmeter should read 0 ohms. Now, start the engine.
I f there is oil pressure, the ohmmeter reading should
increase. I f sending unit fails either test, replace
sending unit.
COMBINATION SENDING UNIT GAUGE FUNCTION TEST
To test the combination oil pressure sending unit
gauge function, unplug the connector. Measure the
resistance between the sending unit sending unit ter­
minal (Fig. 5) and the metal housing (Figs. 6, 7 and
8). The ohmmeter should read higher than 65 ohms.
Now, start the engine. The ohmmeter should read be­
tween 24.5 and 65 ohms, depending on engine speed,
oil temperature, and oil viscosity. I f sending unit fails
either test, replace sending unit.
LOW OIL PRESSURE WARNING LAMP
CIRCUIT TEST
Perform Combination Sending Unit Lamp Function
Test before proceeding with circuit test.
(1) Unplug connector from sending unit (Figs. 6, 7,
and 8) and turn ignition switch to ON. Lamp should
be off. I f OK, continue to next step. I f not OK, repair
circuit for short to ground.
SWITCH
(LIGHT)
SENDING UNIT
(GAUGE)
898E-2
Fig. 5 Combination Oil Pressure Sending Unit
Terminals
(2) Using a jumper wire, ground switch cavity of
connector (Fig. 5) to engine. The lamp should light. I f
OK, check sending unit. I f not OK, turn ignition
switch OFF, remove jumper wire and continue with
next step.
(3) Pull instrument cluster from dash. Do not un­
plug cluster connectors. Refer to Instrument Cluster
Replacement for removal procedures.
(4) Check continuity between sending unit connec­
tor switch cavity (Fig. 5) and oil pressure lamp
ground terminal (Figs. 9 or 10) on back of cluster.
There should be continuity. I f OK, continue to next
step. I f not OK, go to step (6).
(5) With ignition switch i n ON position, check for
battery voltage at oil pressure lamp B+ terminal
(Figs. 9 or 10) on back of cluster. I f OK, replace bulb.
I f not OK, continue to next step.
(6) Unplug cluster connector B (black). With igni­
tion switch i n OFF position and jumper wire from
step (2) installed, check for continuity to ground at
cluster connector cavity #4. I f OK, remove jumper
wire and continue to next step. I f not OK, repair
open circuit to sending unit.
(7) Turn ignition switch to ON. Check for battery
voltage at cluster connector B, cavity #8. I f OK, re­
place cluster printed circuit board. I f not OK, repair
circuit to fuse #12.
OIL PRESSURE GAUGE CIRCUIT TEST
Perform Combination Sending Unit Gauge Func­
tion Test before proceeding with circuit test.
CAUTION: When connecting an input terminal to
ground, DO NOT leave the connection grounded for
more than a few seconds.
(1) Unplug connector from sending unit (Figs. 6, ^,
and 8) and turn ignition switch to ON. Gauge should
read at or below minimum. I f OK, continue to next
step. I f not OK, go to step (3).
(2) Using a jumper wire, ground sending unit cav­
ity of sending unit connector (Fig. 5) to engine. The
gauge should read at or above maximum. I f OK,