Jeep Cherokee

 Service Manual

Overhead console systems » 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.

Trip computer, compass, and thermometer display module

Thermometer