Compass Mini Trip Computer Indicates Erroneous Average Miles Per Gallon,
Distance To Empty, And/Or Trip Odometer
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).
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).
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
1 55350660AE Computer, Compass Mini Trip, without
vehicle theft alarm.
1 55350003AE Computer, Compass Mini Trip, with
vehicle theft alarm.
The repair procedure is to replace the compass/ minitrip computer in
the overhead console and to recalibrate the compass.
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.
- Disconnect and isolate the battery negative cable(s) (two for diesel).
- Open the garage door storage bin door and locate the two overhead console
latch tabs near the front bin (Fig 2).
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.
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.
Remove three screws that secure the compass mini trip computer to the overhead
console housing (Fig 3).
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.
Separate the compass mini trip computer from the overhead console.
Position the new compass mini trip computer onto the overhead console.
Connect the overhead console's wire harness connector to the compass mini
Install and tighten to 20 in-lbs (2.2 Nm) the three screws that secure
the compass mini trip computer to the overhead console.
Position the overhead console near the mounting location on the headliner
in the vehicle.
Connect the roof wire harness connector to the overhead console's wire
Engage the two mounting hooks on the rear of the overhead console housing
in the mounting holes in the inner roof panel.
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.
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
Close the garage door opener storage bin door.
Connect the negative battery cables(s) and reset the clock and radio.
Start the engine and momentarily depress and
release the STEP button until the compass/temperature mode is displayed.
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
- NOTE: The latch tabs may be difficult to depress completely enough
to release the overhead console. Ensure that the latch tabs have released
the overhead console completely before pulling the console downward away
from the roof panel.
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
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.
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.
After 5 seconds, the displayed zone will automatically be set into the
compass mini trip computer module's memory and normal operation will resume.
- NOTE: If the cal message remains in the display, there could be excessive
magnetism near the compass. Repeat the calibration a different location.
If the CAL is still displayed, perform the compass demagnetization procedure.
Refer to the 1999 Ram Truck Service Manual pages 8V-9 and 8V-10 for instructions.
Policy: Reimbursable within the provisions of the
Thanks to Bob Bergevin for providing this TSB information
This page was edited on: May 3, 2004