Dodge Ram 2004 Service Manual page 24

GENERAL INFORMATION
• The ignition switch must be in the On position
and the CMTC display must not be blank.
• If the compass/temperature data is not currently
being displayed, momentarily press and release
the C/T button to display compass/temp informa-
tion.
• Press and hold the RESET button until VARI-
ANCE = XX is displayed. The CMTC will display
the variance zone stored in memory and the word
VARIANCE.
• Use the STEP button to select the proper vari-
ance zone number, 1 through 15.
•
After selecting the proper zone number, momen-
tarily press and release the RESET button. The
variance zone is then stored in the memory and
the CMTC returns to normal operation.
COMPASS CALIBRATION
The compass module has 2 types of auto-
calibration; slow-cal and fast-cal. Slow-cal ensures
that during normal vehicle operation the compass
performs auto-calibration functions to keep the
compass sensors in their proper operating range.
Whenever the ignition is On and the CMTC receives
PCI bus data indicating that engine RPM is greater
than zero, auto-calibration is performed continu-
ously.
If the calibration information stored in the com-
pass module memory is not within the normal
range after a power-up cycle, the compass will
display CAL. The CMTC will enter into the fast-cal
mode until calibration is complete.
To enter the compass into Manual Calibration
mode, perform the following steps:
• Drive the vehicle to an area away from any large
metal objects or overhead power lines.
• Ensure that the proper variance zone is selected.
See Setting Magnetic Zone Variance.
• The ignition switch must be in the On position
and the CMTC display must not be blank.
• Press the C/T button to view the Compass/
Temperature display.
• Press and hold the RESET button until CAL is
displayed, then release the button.
• Drive slowly, less than 5 MPH (8KPH) in at least
1 complete 360-degree circle.
• CAL will remain illuminated to alert the driver
that the compass is in the calibration mode.
• After calibration is complete, CAL will turn off.
If the compass appears blank, unable to be cali-
brated, or the compass displays false indications,
the vehicle must be demagnetized. Refer to Com-
pass Demagnetizing Procedure in the Service Man-
ual.
SELF-CHECK DIAGNOSTICS
The CMTC is capable of performing a diagnostic
self check on its internal functions. CMTC diagnos-
tics may be performed using a DRBIII or by using
the following procedure:
1. With the ignition switch in the OFF position,
depress and hold the RESET and the C/T but-
tons.
2. Turn the ignition switch to the ON position.
3. Continue to hold both buttons until the software
versions are displayed, then release the buttons.
4. All of the VFD segments will illuminate for 2-4
seconds. Check for segments that do not illumi-
nate or illuminate all the time.
5. When the self-check is complete the CMTC will
display one of the following messages:
• PASS
•
FAIL
•
NO BUS
6. To exit the self-check mode, depress the RESET
button or cycle the ignition switch and the
CMTC will return to normal operation.
If a Communication fault is displayed, refer to the
symptom list. If a FAILED SELF TEST is dis-
played, the CMTC must be replaced.
AMBIENT TEMPERATURE SENSOR
The ambient air temperature is monitored by the
FCM or the PCM and displayed by the CMTC. For
Diesel equipped vehicles, the FCM receives a hard-
wire input from the ambient temperature sensor
(ATS). For 3.7L, 4.7L and 5.7L equipped vehicles,
the PCM receives the hardwire input from the ATS.
The ATS is a variable resistor that operates on a
5-volt reference signal circuit hardwired from the
FCM or PCM. The resistance in the ATS changes as
the outside temperature rises or falls. The FCM or
PCM senses the change in reference voltage
through the ATS resistor. Based on the resistance of
the ATS, the FCM or PCM is programmed to corre-
spond to a specific temperature. The FCM or PCM
stores and filters the ambient temperature data
and transmits this data to the CMTC via the PCI
Bus. The ATS cannot be adjusted or repaired and, if
faulty or damaged, it must be replaced.
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