B0180

Circuit Description

The output air temperature sensor # 1 (upper) is a thermistor used to control the signal voltage in the heater and A/C control module. The heater and A/C control module supplies a reference voltage (about 5 volts) on CKT 404 to the sensor. When the upper duct air temperature is cold, the thermistor resistance is high. Therefore, the heater and A/C control module will receive a high voltage input. If the upper duct air temperature is hot, the thermistor resistance is low. Therefore, the heater and A/C control module will receive a low signal voltage input. The output air temperature sensor # 1 (upper) is used to enhance the temperature control. Refer to Sensor Resistance Table. Sensor Resistance Tables - Electronic Climate Control (ECC)

Conditions for Setting the DTC

When the ignition is ON, the heater and A/C control module will detect this fault any time that CKT 404 is at or near 5 volts or higher.

Action Taken When the DTC Sets

The heater arid A/C control module will use a default value of 10 A/D counts until the fault is cleared.

Conditions for Clearing the MIL/DTC

This fault will clear as soon as DTC 8180 goes away or has been repaired. The system will then return to normal operation. History DTCs can only be cleared by removing and restoring B+ or by using the scan tool.

Diagnostic Aids

- The heater and A/C control module may set class 2 lost communication DTCs when the Body Control Module (BCM) or the VCM is being reprogrammed. After reprogramming, inspect for DTCs in +he heater and A/C control module. Clear any history U DTCs, then resume diagnostics.
- Visually inspect the sensor connector and harness for corrosion and damage. The resistance value of the sensor must be 334-100,865 Ohms. Refer to the Temperature vs Resistance Table. If resistance is not within specifications replace the sensor.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This step measures resistance of output air temperature sensor # 2.
2. This step inspects for a short to ground in CKT 405.
3. This step inspects for Intermittents and tests for a malfunctioning heater and A/C control module.
4. This step repairs the short to ground in CKT 405.
5. This step replaces defective output air temperature sensor # 2.
6. This step replaces a defective heater and A/C control module.