Central Timer Module
SELF-CHECK DIAGNOSTICS
The CMTC is capable of performing a diagnostic self check on its internal functions. CMTC diagnostics may be performed using a DRB III (R) or by using the following procedure:
1. With the ignition switch in the OFF position, depress and hold the RESET and the STEP buttons.
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 illuminate or illuminate all the time.
5. When the self-check is complete the CMTC will display one of the following messages:
- PASS SELF TEST
- FAILED SELF TEST
- NOT RECEIVING J1850 MESSAGE
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 displayed, the CMTC must be replaced.
AMBIENT TEMPERATURE SENSOR
The ambient air temperature is monitored by the NGC in 3.7L and 4.7L vehicles, or by the HVAC module in JTEC equipped vehicles, and is displayed by the CMTC. The NGC or HVAC module receives a hard wire input from the ambient temperature sensor (ATS).
The ATS is a variable resistor that operates on a 5-volt reference signal circuit hardwired from the NGC or the HVAC module. The resistance in the ATS changes as the outside temperature rises or falls. The NGC or HVAC module senses the change in reference voltage through the ATS resistor. Based on the resistance of the ATS, the NGC or HVAC module is programmed to correspond to a specific temperature. The NGC or HVAC module 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.
AMBIENT TEMPERATURE SENSOR FAULT CODES
The outside temperature function is supported by the ambient temperature sensor (ATS), a signal and ground circuit hardwired to the NGC or HVAC module, and the CMTC display.
If the CMTC display indicates 54Deg C (130 ° F) or the ATS sense circuit is shorted to ground, the temp display will be 54Deg C (130 Deg F) to indicate a SHORT circuit condition.
If the CMTC display indicates -40Deg C (-40 ° 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 NGC or HVAC module. Ambient Temperature Sensor DTCs will be recorded in the NGC or HVAC module. The ATS can be diagnosed using the following Sensor Test. Test the ATS circuits using the diagnostics in the Body Diagnostic Procedures. If the CMTC passes the self test, and the ATS, the circuits, and PCI bus communications are confirmed to be OK, but the CMTC temperature display is inoperative or incorrect, replace the NGC or HVAC module.
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 mini/max values:
- 0Deg C (32 Deg F) Sensor Resistance = 29.33 - 35.99 Kilohms
- 10Deg C (50 Deg F) Sensor Resistance = 17.99 - 21.81 Kilohms
- 20Deg C (68 Deg F) Sensor Resistance = 11.37 - 13.61 Kilohms
- 25Deg C (77 Deg F) Sensor Resistance = 9.12 - 10.86 Kilohms
- 30Deg C (86 Deg F) Sensor Resistance = 7.37 - 8.75 Kilohms
- 40Deg C (104 Deg F) Sensor Resistance = 4.90 - 5.75 Kilohms
The sensor resistance should read between these min/max values. If the resistance values are not OK, replace the Sensor.