Cooldown Test Sensor Failure (MTC)

COOLDOWN TEST SENSOR FAILURE (MTC)





For a complete wiring diagram Consult Diagrams/Electrical

- When Monitored:
When the Cooldown Test is executed.

- Set Condition:
If the A/C Heater Control detects either abnormally high or low voltage on the (C21) Evaporator Temperature Sensor Signal circuit.





Diagnostic Test

1. CHECK FOR HVAC DTCs
Turn the ignition on.
With the scan tool, read HVAC DTCs.
Does the scan tool display any DTCs?

Yes

- Diagnose and Repair the DTC(s).
- Run the Cooldown Test after the repair is complete.
- Perform BODY VERIFICATION TEST - VER 1. Body Verification Test.

No

- Go To 2

2. CHECK EVAPORATOR TEMPERATURE SENSOR RESISTANCE




Turn the ignition off.
Disconnect the A/C Heater Control C1 harness connector.
Measure the resistance between the (C21) Evaporator Temperature Sensor Signal circuit and the (C121) Sensor Ground circuit. The approximate circuit resistance should be:
1,468 ohms @ 40°C (104°F).
1,800 ohms @ 35°C (95°F).
2,221 ohms @ 30°C (86°F).
2,757 ohms @ 25°C (77°F).
3,443 ohms @ 20°C (68°F).
4,330 ohms @ 15°C (59°F).
5,485 ohms @ 10°C (50°F).
7,354 ohms @ 4°C (39°F).
8,130 ohms @ 2°C (36°F).
Is the resistance within the specifications?

Yes

- Reconnect the A/C Heater Control C1 harness connector. Then, Go To 3

No

- Check the related circuits and connectors for conditions that would cause either a high or low resistance. Repair as necessary. If okay, replace the Evaporator Temperature Sensor.
- Run the Cooldown Test after the repair is complete.
- Perform BODY VERIFICATION TEST - VER 1. Body Verification Test.

3. VERIFY ALL COOLDOWN TEST PREREQUISITES WERE MET & RUN THE TEST AGAIN
NOTE: The following are prerequisites of the Cooldown Test. Verify each of the following before running the test:
- If active, diagnose and repair DTC Evaporator Temperature Sensor Circuit Open or DTC Evaporator Temperature Sensor Circuit Shorted before proceeding.
- Verify that the refrigerant system has an adequate charge. Check and repair as necessary before proceeding. Refrigerant System Leaks
- Verify that the blower motor operates correctly in all speeds. Diagnose and repair all blower related faults before proceeding.
- Verify that the work area ambient temperature is above 21.1°C (70°F) before proceeding. Move the vehicle to a warmer work area if necessary.
- Verify that the evaporator temperature is above 13°C (55°F) before proceeding.
- Verify that the A/C compressor is not running. If the A/C compressor is running, turn the A/C off and allow the evaporator to warm up before proceeding.


Once all of the prerequisites have been met, start the engine and actuate the Cooldown Test with the scan tool.

NOTE: The Cooldown Test can take up to two minutes to run. While the test is running, the A/C status indicator will flash. If the test fails, the status indicator will continue to flash until either a successful test is performed, or any button on the control is pressed, or the ignition is cycled and the odometer displays more than eight miles. When the test is complete, the scan tool will display one or more test status messages to indicate the outcome of the test. These messages will clear from memory, so note all messages before exiting the test.

Allow the test to run to completion before proceeding.
Does the Cooldown Test Sensor Failure status message reset?

Yes

- Replace the A/C Heater Control.
- Run the Cooldown Test after the repair is complete.
- Perform BODY VERIFICATION TEST - VER 1. Body Verification Test.

No

- Perform additional testing as necessary.
- Perform BODY VERIFICATION TEST - VER 1. Body Verification Test.