Dodge Ram Truck 1500-2500-3500. Manual - part 394

dimmer controlled gauge lighting with the exterior lamps turned On, the black graphics appear blue-green and the
red graphics still appear red. The gauge needle has internal optical illumination.

The oil temperature gauge cannot be repaired or adjusted and, if damaged or faulty, it must be replaced. The gauge
illumination LED unit is not available for service replacement and, if damaged or faulty, the entire gauge must be
replaced.

OPERATION

The oil temperature gauge gives an indication to the
vehicle operator of the engine oil temperature. This
gauge is controlled by its own internal electronic circuit
board based upon a hard wired input received by the
gauge from an oil temperature sensor (4) installed in a
tapped hole that penetrates an oil passage on the
right side of the engine block (2) just behind the oil
pressure sensor (3).

The oil temperature sensor is a Negative Temperature
Coefficient (NTC) thermistor that changes its internal
resistance with changes in temperature. The sensor
has two terminals. One terminal receives a hard wired
ground path through a take out and connector of the
engine wire harness (1), and the second terminal pro-
vides a variable output to the gauge through the same
take out and connector. As the oil temperature
increases the resistance of the sensor decreases, and
as the oil temperature decreases the resistance of the
sensor increases.

The oil temperature gauge is an air core magnetic unit. The gauge pigtail wire and connector provides the gauge
electronic circuit board with a hard wired ground path, battery current through a fused ignition switch output (run-
start) circuit, a Pulse Width Modulated (PWM) panel lamps dimmer input from the instrument cluster for general
illumination, and the input from the oil temperature sensor. This gauge is only operational when the ignition switch
is in the On or Start positions. The gauge electronic circuit board reads the input from the oil temperature sensor,
then provides linear positioning of the gauge needle on the gauge scale based upon that input. The gauge elec-
tronics will move the gauge needle back to the low end of the scale after the ignition switch is turned to the Off
position.

The oil temperature gauge and the oil temperature sensor may be diagnosed using conventional diagnostic tools
and methods. Refer to the appropriate diagnostic information.

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DIAGNOSIS AND TESTING

OIL TEMPERATURE GAUGE

WARNING: To avoid personal injury or death, on vehicles equipped with airbags, disable the supplemental
restraint system before attempting any steering wheel, steering column, airbag, seat belt tensioner, impact
sensor, or instrument panel component diagnosis or service. Disconnect and isolate the battery negative
(ground) cable, then wait two minutes for the system capacitor to discharge before performing further diag-
nosis or service. This is the only sure way to disable the supplemental restraint system. Failure to take the
proper precautions could result in accidental airbag deployment.

The hard wired oil temperature gauge and gauge lighting circuits may be diagnosed and tested using conventional
diagnostic tools and procedures. Refer to the appropriate wiring information. The wiring information includes wiring
diagrams, proper wire and connector repair procedures, details of wire harness routing and retention, connector
pin-out information and location views for the various wire harness connectors, splices and grounds.

NOTE: When testing the oil temperature gauge by alternately opening and shorting the oil temperature sen-
sor signal circuit, the gauge pointer may rotate in either direction (clockwise or counterclockwise) to reach
the objective point on the gauge scale. This is a normal condition as the gauge electronics are programmed
to move the pointer from its current position to the objective position in the direction that provides the
shortest pointer travel distance.

CONDITION

POSSIBLE CAUSES

CORRECTION

OIL TEMPERATURE GAUGE

DOES NOT ILLUMINATE WITH

EXTERIOR LIGHTING TURNED

1. Faulty panel lamps dimmer
circuit.

1. Test and repair open oil temperature
gauge panel lamps dimmer circuit as
required.

2. Faulty ground circuit.

2. Test and repair open oil temperature
gauge ground circuit as required.

3. Faulty Light Emitting Diode
(LED) in gauge.

3. Replace the faulty oil temperature gauge
as required.

OIL TEMPERATURE GAUGE

NEEDLE DOES NOT GIVE ANY

INDICATION WITH ENGINE AT

OPERATING TEMPERATURE

AND IGNITION SWITCH ON.

1. Faulty signal circuit.

1. Test and repair shorted oil temperature
sensor signal circuit as required.

2. Faulty supply circuit.

2. Test and repair open oil temperature
gauge fused ignition switch output
(run/start) circuit as required.

3. Faulty sensor.

3. Test and replace faulty oil temperature
sensor as required.

4. Faulty gauge.

4. Replace the faulty oil temperature gauge
as required.

OIL TEMPERATURE GAUGE

NEEDLE ALWAYS INDICATES

HIGH WITH IGNITION SWITCH

ON.

1. Disconnected sensor.

1. Reconnect oil temperature sensor as
required.

2. Faulty signal circuit.

2. Test and repair open oil temperature
sensor signal circuit as required.

3. Faulty sensor ground.

3. Test and repair open oil temperature
sensor ground circuit as required.

4. Faulty sensor.

4. Test and replace faulty oil temperature
sensor as required.

5. Faulty gauge.

5. Replace the faulty oil temperature gauge
as required.

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OIL TEMPERATURE SENSOR

1. Disconnect the engine wire harness connector from the oil temperature sensor.

2. Using an ohmmeter and a test thermometer, test the resistance versus the oil temperature relationship of the

sensor between the two terminals of the sensor as shown in the Oil Temperature Sensor Tests table.

OIL TEMPERATURE SENSOR TESTS

TEMPERATURE

RESISTANCE RANGE (KILOHMS)

°C

°F

(40)

291.49 - 381.71

(20)

(4)

85.85 - 108.39

(10)

49.25 - 61.43

29.33 - 35.99

17.99 - 21.81

11.37 - 13.61

9.12 - 10.88

7.37 - 8.75

104

4.90 - 5.75

122

3.33 - 3.88

140

2.31 - 2.67

158

1.63 - 1.87

176

1.17 - 1.34

194

0.86 - 0.97

100

212

0.64 - 0.72

110

230

0.48 - 0.54

120

248

0.37 - 0.41

130

266

0.28 - 0.32

3. If the sensor fails any of these tests, replace the faulty oil temperature sensor as required.

REMOVAL

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1. Disconnect and isolate the battery negative cable.

2. Remove the trim molding (5) from the inside of the

left A-pillar. (Refer to 23 - BODY/INTERIOR/A-PIL-
LAR TRIM - REMOVAL).

3. Remove the two nuts (2) that secure the oil tem-

perature gauge (4) mounting studs to the mounting
bracket (1) on the back of the A-pillar trim.

4. Remove the four screws (3) that secure the mount-

ing bracket to the back of the A-pillar trim.

5. Remove the mounting bracket from the back of the

A-pillar trim.

6. Push the gauge and the gauge pigtail wire (6) and

connector out through the mounting hole on the
face of the A-pillar trim.

INSTALLATION

1. Position the oil temperature gauge (4) into the

mounting hole on the face of the A-pillar trim (5).

2. Position the mounting bracket (1) to the back of the

A-pillar trim with the gauge pigtail wire (6) and con-
nector routed between the two lower mounting
bracket screw bosses on the back of the A-pillar
trim.

3. Install and tighten the four screws (3) that secure

the mounting bracket to the back of the A-pillar
trim. Tighten the screws to 1 N·m (9 in. lbs.).

4. Align and insert the two mounting studs on the

back of the gauge housing through the appropriate
holes in the mounting bracket.

5. Install and tighten the two nuts that secure the

gauge mounting studs to the mounting bracket.
Tighten the nuts to 0.5 N·m (5 in. lbs.).

6. Reinstall the trim molding onto the inside of the left

A-pillar. (Refer to 23 - BODY/INTERIOR/A-PILLAR
TRIM - INSTALLATION).

7. Reconnect the battery negative cable.

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