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TSB 08-51-98

Compass Mini Trip Computer Indicates Erroneous Average Miles Per Gallon,
Distance To Empty, And/Or Trip Odometer

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Date: Nov 27, 1998

Models: 1999 (BR/BE) Ram Trucks

NOTE-. THIS BULLETIN APPLIES TO VEHICLES EQUIPPED WITH THE COMPASS MINI TRIP COMPUTER (SALES CODE CUS).

Symptom./Condition:

The compass mini trip computer indicates inaccurate Average Miles Per Gallon and Distance To Empty when the compass mini trip computer is allowed to calculate the average miles per gallon over an extended mileage period (approximately 1609 km (1000 miles)) without a reset.

The trip odometer and the elapsed time on the compass mini trip computer can display erroneous numbers in the third digit from the right. If the number 7 (seven) is displayed in the fourth digit from the right, the third digit will illuminate the lower horizontal bar segment. Example shown below (Figure 1).

Diagnosis: 

To check the first condition, the vehicle must be driven for approximately 1000 miles (1600 km) without resetting the trip odometer.

To duplicate the second condition, the trip odometer must not be reset for at least 710 km/miles.

If a customer indicates that their trip computer provides inaccurate Average Miles Per Gallon and/or inaccurate Distance to Empty, or indicates that the trip odometer or elapsed time feature displays the lower portion of the third segment when a 7 is displayed in the fourth digit, perform the repair.

Parts:

1    55350660AE   Computer, Compass Mini Trip, without vehicle theft alarm.
1    55350003AE   Computer, Compass Mini Trip, with vehicle theft alarm.

Repair Procedure:

 The repair procedure is to replace the compass/ minitrip computer in the overhead console and to recalibrate the compass.

  1. Disconnect and isolate the battery negative cable(s) (two for diesel).
  2. Open the garage door storage bin door and locate the two overhead console latch tabs near the front bin (Fig 2).
  3. While pulling gently downward on the front of the overhead console, push the latch tabs forward until each latch is disengaged from its receptacle in the inner roof panel.
  4. Slide the console rearward far enough to disengage the two mounting hooks on the rear of the housing from the mounting holes on the inner roof panel.
  5. Lower the console from the headliner far enough to access the wire harness connector. Then disconnect the connector and separate the overhead console from the vehicle.
  6. Remove three screws that secure the compass mini trip computer to the overhead console housing (Fig 3).
  7. Pull the compass mini trip computer away from the overhead console far enough to access the wire harness connector. Then disconnect the connector from the compass mini trip computer.
  8. Separate the compass mini trip computer from the overhead console.
  9. Position the new compass mini trip computer onto the overhead console.
  10. Connect the overhead console's wire harness connector to the compass mini trip computer.
  11. Install and tighten to 20 in-lbs (2.2 Nm) the three screws that secure the compass mini trip computer to the overhead console.
  12. Position the overhead console near the mounting location on the headliner in the vehicle.
  13. Connect the roof wire harness connector to the overhead console's wire harness connector.
  14. Engage the two mounting hooks on the rear of the overhead console housing in the mounting holes in the inner roof panel.
  15. Slide the overhead console forward far enough to align the two latches on the front of the housing with their receptacles in the inner roof panel.
  16. Push upward firmly and evenly on the front of the overhead console until each of the two latches are fully engaged in its receptacle in the inner roof panel.
  17. Close the garage door opener storage bin door.
  18. Connect the negative battery cables(s) and reset the clock and radio.
  19. Start the engine and momentarily depress and release the STEP button until the compass/temperature mode is displayed.
  20. Drive the vehicle on a level surface away from large metal objects and power lines through three or more complete circles that are 30-90 ft (9-27 m) in diameter. Up to ten complete circles in both clockwise and counterclockwise direction may be required for a complete calibration. The vehicle speed must be maintained between 5-11 mph (8-17 kph). Once the compass detects that a calibration is taking place, CAL will be displayed. When the calibration is complete, CAL will disappear from the display and normal compass operation will resume.
  21. Once the calibration is complete, the compass may need to have its variance set. Compass variance, also known as magnetic declination, is the difference in angle between true geographic north and magnetic north. In some locations, the difference between true north and magnetic north is great enough to give false readings on the compass display. If this occurs, the variance should be set.
  22. To set variance, ensure that the compass/temperature information is displayed. Then momentarily depress the US/Metric and the step buttons simultaneously for at least 100 milliseconds but not more than one second. The compass will enter into the variation adjustment mode and display the current variance zone along with VAR.
  23. Depress and release the step button to step through the zone number until the zone number for your geographic area appears in the display. Refer to Fig 4 for geographic zone variance settings.
  24. After 5 seconds, the displayed zone will automatically be set into the compass mini trip computer module's memory and normal operation will resume.

Notes:

Policy:    Reimbursable within the provisions of the warranty


Thanks to Bob Bergevin for providing this TSB information

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This page was edited on: May 3, 2004