Trip Computer: Description and Operation

The JR Compass Mini-Trip Computer (CMTC) is located in the instrument panel between the center A/C outlets. The CMTC has two function buttons and a vacuum fluorescent (VF) display that provides the outside temperature, Trip Computer information, and one of eight compass headings to indicate the direction the vehicle is facing. The compass heading and the outside temperature are displayed at the same time.

The BCM calculates much of the information displayed by the CMTC. The BCM receives this information from PCI Bus messages, the PCM, and the Ambient Temperature Sensor. The Ambient Temperature Sensor (ATS) monitors the outside temperature and is hardwired to the PCM. The CMTC receives filtered outside temperature data via PCI Bus messages from the BCM. The ambient temperature sensor may receive invalid data whenever the vehicle is operated at low speeds, or the ignition is off for a short period of time. These causes for inaccuracy will be filtered out by the BCM.

The CMTC receives dedicated PCI Bus messages with the calculated information from the BCM for the trip computer displays.

The CMTC cannot be repaired and, if faulty or damaged it must be replaced. The incandescent lamp for the STEP and US/M button illumination is serviceable.

Actuation of the STEP button will cause the CMTC to change modes of operation. Actuation of the USN button will toggle the display between English and Metric units. Trip Computer resets are accomplished by pressing the STEP and US/M buttons simultaneously. To reset only the trip information currently being displayed,press and release the STEP and US/M buttons simultaneously for one second until the chime sounds. To reset all trip information, press and hold the STEP and US/M buttons simultaneously until a second chime sounds (approximately 2 seconds) and then release the buttons.

The CMTC operates only when the ignition is on. The following functions are available using the STEP button:
- Compass and outside temperature
- Average fuel economy (AVE ECO)
- Instantaneous Fuel Economy (ECO)
- Distance to Empty (DTE)
- Trip Odometer (ODO)
- Elapsed ignition time (ET)
- Display Off

C0MPASS/MINI-TRIP C0MPUTER VF DISPLAY MESSAGES
The CMTC will not display information for any of the screens for which it did not receive the proper PCI bus data. Refer to the symptom list in the Diagnostic for problems related to the CMTC.

The CMTC receives the following messages from Body Control Module (BCM):
- Verification of US/Metric status
- VF display dimming brightness and exterior lamp status
- Trip Odometer data
- Elapsed Ignition On Time data
- Fuel Economy (Average and Instantaneous)
- Distance to Empty
- Outside Temperature

The CMTC transmits the following messages to the BCM:
- Status Request: Beep, Reset, US/M Toggle
- Current Display
- Compass Heading

The CMTC receives the following message from PCM:
- Vehicle Speed

SETTING MAGNETIC ZONE VARIANCE
Variance is the difference between magnetic North and geographic North. For proper compass function, the correct variance zone must be set. Refer to the Zone Variance map for the correct zone. Follow these steps to check or change the variance zone:
- The ignition switch must be in the On position and the CMTC display must not be blank.
- Press and hold the STEP and US/M buttons until VAR is displayed. The CMTC will display the last variance zone stored in memory and the word VAR.
- Use the STEP button to select the proper variance zone number, 1through 15.
- After selecting the proper zone number, simultaneously Press the STEP and US/M buttons wait approximately 15 seconds. 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 continuously.

If the calibration information stored in the compass module memory is not within the normal range after a power-up cycle, the compass will display CAL. The CMTC with 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 STEP button and scroll to the Compass/Temperature display.
- Press and hold the STEP and US/M buttons simultaneously until CAL begins flashing and then release the buttons.
- CAL is displayed without flashing.
- Drive slowly, less than 4 MPH (8KPH) in 3 complete 360 degree circles.
- 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 unable to be calibrated or the compass displays false indications, the vehicle may need to be demagnetized.

AMBIENT TEMPERATURE SENSOR
The ambient air temperature is monitored by the PCM and displayed by the CMTC. The PCM receives a hardwired input from the ambient temperature sensor (ATS). The ATS is located on the inside of the front bumper beam.

The ATS cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

The ATS is a variable resistor that operates on a 5-volt reference signal circuit hardwired from the PCM. The resistance in the ATS changes as the outside temperature rises or falls. The PCM senses the change in reference voltage through the ATS resistor. Based on the resistance of the ATS, the PCM is programmed to correspond to a specific temperature. The PCM then transmits the proper ambient temperature to the BCM. The BCM filters the ambient temperature data and transmits this data to the CMTC.

DIAGNOSIS AND TESTING

SELF-CHECK DIAGNOSTICS
The CMTC is capable of performing a diagnostic self check on its internal functions. CMTC diagnostics may be performed using a DRBIII(R) or by using the following procedure:
1. With the ignition switch in the OFF position,depress and hold the STEP and the US/M buttons.
2. Turn the ignition switch to the On position and release the buttons.
3. of the VFD segments will illuminate for 2-4 seconds. Check for segments that do not illuminate or illuminate all the time.
4. When the self-check is complete the CMTC will display one of the following five messages:
- F (FAIL)
- P (PASS)
- Bus (No PCI bus communication)
- Bus 1 (No PCM bus messages received)
- Bus 2 (No BCM bus messages received)
5. To exit the self-check mode, depress the STEP button or cycle the ignition switch and the CTM will return to normal operation.

If a Bus fault is displayed, refer to the symptom list. If an F is displayed, the CMTC must be replaced. The CMTC will not display an F for a VF segment that does not illuminate.

AMBIENT TEMPERATURE SENSOR
The outside temperature function is supported by the ambient temperature sensor (ATS), a signal and ground circuit hardwired to the PCM, the BCM, and the CMTC display.

If the CMTC display indicates 60° C (140° F) or the ATS sense circuit is shorted to ground, the temp display will be 60° C (140° F) to indicate a SHORT circuit condition.

If the CTM display indicates -45° C (-49° F) or the ATS sense circuit is open, the temp display will be -45° C (-49° F) to indicate an OPEN circuit condition.

If there is an OPEN or SHORT circuit condition, it must be repaired before the CMTC VFD can be tested. The ATS is supported by the PCM. ATS fault DTC's will be recorded in the PCM.

The ATS can be diagnosed using the following Sensor Test. Test the ATS circuits using the diagnostics in the Body Diagnostic Procedures Manual. If the ATS, the circuits, and PCI bus communications are con- firmed to be OK, but the CMTC temperature display is inoperative or incorrect, replace the CMTC.


AMBIENT TEMPERATURE SENSOR TEST
1. Turn the ignition OFF.
2. Disconnect the ATS harness connector.
3. Measure the resistance of the ATS using the following mid max values:
- 0° C°(32° F) Sensor Resistance = 29.33 - 35.99 Kilohms
- 10° C(50° F) Sensor Resistance = 17.99 - 21.81 Kilohms
- 20° C(68° F) Sensor Resistance = 11.37 - 13.61 Kilohms
- 25° C(77° F) Sensor Resistance = 9.12 - 10.86 Kilohms
- 30° C(86° F) Sensor Resistance = 7.37 - 8.75 Kilohms
- 40° C(104° F) Sensor Resistance = 4.90 - 5.75 Kilohms

The sensor resistance should read between these mid max values. If the resistance values are no OK, replace the Sensor.