Diagnostic Routine F

Diagnostic Routine F

Diagnostic Overview

B1B71:11, B1B71:15

Refer to Wiring Diagram Set 55 for schematic and connector information Electrical Diagrams.

Normal Operation and Fault Conditions

The evaporator discharge air temperature sensor receives a ground from the HVAC (Heating, Ventilation, and Air Conditioning) module. The sensor varies its resistance with the temperature. As the temperature rises, the resistance falls. As the temperature falls, the resistance rises. The HVAC (Heating, Ventilation, and Air Conditioning) module measures this resistance to determine the temperature at the sensor.

The evaporator discharge air temperature sensor is used for A/C (Air Conditioning) compressor cycling. An accurate evaporator temperature is critical to prevent evaporator icing. The HVAC (Heating, Ventilation, and Air Conditioning) module uses the temperature measurement to turn off the A/C (Air Conditioning) compressor before the evaporator temperatures are cold enough to freeze the condensation. This prevents ice blockage of airflow over the evaporator core.

DTC Fault Trigger Conditions






Pinpoint Test

1. CHECK THE HVAC (Heating, Ventilation, and Air Conditioning) MODULE OUTPUT VOLTAGE

1. Ignition ON.

2. Press the POWER button on the HVAC (Heating, Ventilation, and Air Conditioning) controls.

3. Measure:





Is the voltage between 4.7 and 5.1 volts?








2. CHECK THE EVAPORATOR TEMPERATURE SENSOR FEEDBACK CIRCUIT FOR A SHORT TO VOLTAGE

1. Ignition OFF.

2. Disconnect: HVAC (Heating, Ventilation, and Air Conditioning) Module C228A.

3. Ignition ON.

4. Measure:





Is any voltage present?








3. CHECK THE EVAPORATOR TEMPERATURE SENSOR FEEDBACK CIRCUIT FOR AN OPEN

1. Ignition OFF.

2. Measure:





Is the resistance less than 3 ohms?








4. CHECK THE SIGNAL RETURN CIRCUIT FOR AN OPEN

1. Measure:





Is the resistance less than 3 ohms?








5. CHECK THE EVAPORATOR TEMPERATURE SENSOR FEEDBACK CIRCUIT FOR A SHORT TO THE SIGNAL RETURN CIRCUIT

1. Ignition OFF.

2. Disconnect: HVAC (Heating, Ventilation, and Air Conditioning) Module C228A.

3. Measure:





Is the resistance greater than 10,000 ohms?








6. CHECK THE EVAPORATOR TEMPERATURE SENSOR FEEDBACK CIRCUIT FOR A SHORT TO GROUND

1. Measure:





Is the resistance greater than 10,000 ohms?








7. CHECK FOR CORRECT HVAC (Heating, Ventilation, and Air Conditioning) MODULE OPERATION

1. Ignition OFF.

2. Disconnect and inspect all HVAC (Heating, Ventilation, and Air Conditioning) module connectors.

3. Repair:

- corrosion (install new connector or terminals- clean module pins)
- damaged or bent pins- install new terminals/pins
- pushed-out pins- install new pins as necessary

4. Reconnect the HVAC (Heating, Ventilation, and Air Conditioning) module connectors. Make sure they seat and latch correctly.

5. Operate the system and determine if the concern is still present.

Is the concern still present?