Jeep Cherokee (XJ): Diagnosis and testing

Trip computer, compass, and thermometer display module

If the problem with the trip computer, compass, and thermometer display module is an inaccurate or scrambled display, use the Self-Diagnostic Test procedures.

If the problem is incorrect display lighting levels, use a DRB scan tool and the proper Diagnostic Procedures manual to test for the correct dimming message inputs being received from the instrument cluster over the Chrysler Collision Detection (CCD) data bus. If the problem is a no-display condition, use the following procedures. For circuit descriptions and diagrams, refer to 8W-49 - Overhead Console in Group 8W - Wiring Diagrams.

(1) Check the fuses in the junction block and the Power Distribution Center (PDC). If OK, go to Step 2. If not OK, repair the shorted circuit or component as required and replace the faulty fuse(s).

(2) Turn the ignition switch to the On position.

Check for battery voltage at the fused ignition switch output fuse in the junction block. If OK, go to Step 3.

If not OK, repair the open circuit to the ignition switch as required.

(3) Turn the ignition switch to the Off position.

Disconnect and isolate the battery negative cable.

Remove the overhead console from the headliner.

Check for continuity between the ground circuit cavities of the overhead console wire harness connector and a good ground. There should be continuity. If OK, go to Step 4. If not OK, repair the open circuit to ground as required.

(4) Connect the battery negative cable. Check for battery voltage at the fused B(+) circuit cavity of the overhead console wire harness connector. If OK, go to Step 5. If not OK, repair the open circuit to the junction block as required.

(5) Turn the ignition switch to the On position.

Check for battery voltage at the fused ignition switch output circuit cavity of the overhead console wire harness connector. If OK, proceed to the Self-Diagnostic Test in this group for further diagnosis of the module and the CCD data bus. If not OK, repair the open circuit to the junction block as required.

SELF-DIAGNOSTIC TEST

A self-diagnostic test is used to determine that the trip computer, compass, thermometer, and all of the display module segments are operating properly electrically.

Initiate the self-diagnostic test as follows: (1) With the ignition switch in the Off position, simultaneously press and hold the Step button and the U. S./Metric button.

(2) Turn the ignition switch to the On position.

(3) Continue to hold both buttons until the display module performs a display segment test. In this test, all of the vacuum fluorescent display segments are lighted. This test will: a. Verify that all display segments are functional b. Check the internal circuitry of the module c. Check that all of the CCD data bus messages needed are being received.

(4) Respond to the respective test results as follows.

If all tests are passed, the module will automatically return to normal operation.

a. In the display segment test, if any segment should fail to light the unit is faulty and must be replaced.

b. If the internal circuitry test is failed, the module will display "FAIL". If "FAIL" is displayed, the unit is faulty and must be replaced.

c. If the CCD data bus message test is failed, the module will display "CCD". If "CCD" is displayed, the use of a DRB scan tool and the proper Diagnostic Procedures manual are required for further diagnosis.

(5) Momentarily depress and release either button one time to exit the self-diagnostic test mode and return the trip computer, compass, and thermometer display module to normal operation.

NOTE: If the compass functions, but accuracy is suspect, it may be necessary to perform a variation adjustment. This procedure allows the compass unit to accommodate variations in the earth's magnetic field strength, based on geographic location.

See the Compass Variation Adjustment procedures, in this group.

NOTE: If the compass reading has blanked out, and only "CAL" appears in the display module, demagnetizing may be necessary to remove excessive residual magnetic fields from the vehicle. See the Compass Demagnetizing procedure, in this group.

Thermometer

The thermometer function is supported by a ambient temperature sensor, a wiring circuit, and a portion of the overhead console trip computer, compass, and thermometer display module display. The sensor is mounted outside the passenger compartment near the front and center of the vehicle.

If any portion of the ambient temperature sensor circuit fails, the thermometer display will self-diagnose the circuit. An "SC" (short circuit) will appear in the display in place of the temperature, when the sensor is exposed to temperatures above 55 C (131 F), or if the sensor circuit is shorted. An "OC" (open circuit) will appear in the display in place of the temperature, when the sensor is exposed to temperatures below -40 C (-40 F), or if the sensor circuit is open.

The ambient temperature sensor circuit can also be diagnosed using the following Sensor Test, and Sensor Circuit Test. If the temperature sensor and circuit are confirmed to be OK, but the temperature display is inoperative or incorrect, see the Trip Computer, Compass, and Thermometer Display Module diagnosis in this group. For circuit descriptions and diagrams, refer to 8W-49 - Overhead Console in Group 8W - Wiring Diagrams.

SENSOR TEST

(1) Turn the ignition switch to the Off position.

Disconnect and isolate the battery negative cable.

Unplug the temperature sensor wire harness connector.

(2) Measure the resistance of the temperature sensor.

At -40 C (-40 F), the sensor resistance is 336 kilohms. At 55 C (131 F), the sensor resistance is 2.986 kilohms. The sensor resistance should read between these two values. If OK, go to the Sensor Circuit Test. If not OK, replace the faulty sensor.

SENSOR CIRCUIT TEST

(1) Turn the ignition switch to the Off position.

Disconnect and isolate the battery negative cable.

Unplug the ambient temperature sensor wire harness connector and the overhead console wire harness connector.

(2) Connect a jumper wire between the two terminals in the body half of the sensor wire harness connector.

(3) Check for continuity between the sensor return circuit and the ambient temperature sensor signal circuit cavities of the overhead console wire harness connector. There should be continuity. If OK, go to Step 4. If not OK, repair the open circuit as required.

(4) Remove the jumper wire from the ambient temperature sensor wire harness connector. Check for continuity between the sensor return circuit cavity of the overhead console wire harness connector and a good ground. There should be no continuity. If OK, go to Step 5. If not OK, repair the short circuit as required.

(5) Check for continuity between the ambient temperature sensor signal circuit cavity of the overhead console wire harness connector and a good ground.

There should be no continuity. If OK, see the Trip Computer, Compass, and Thermometer Display Module diagnosis in this group. If not OK, repair the short circuit as required.