• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provides an overview of each diagnostic category.

The evaporator air temperature sensor is a 2-wire negative temperature coefficient thermistor. The HVAC control module provides a low reference circuit and signal circuit. The HVAC control module determines the voltage drop across the sensor, which is proportional to temperature. As the air temperature increases, the sensor resistance decreases and the voltage signal decreases. As the air temperature decreases, the sensor resistance increases and the voltage signal increases.

The ignition is ON.

The HVAC control module detects the sensor signal out of range. The signal voltage is less than 0.1 V or greater than 4.9 V for more than 50 ms.

The system operates using a default value.

• The DTC will become history if the HVAC control module no longer detects a failure.
• The history DTC will clear after 100 fault-free ignition cycles.

HVAC Schematics

Master Electrical Component List

Manual HVAC Description and Operation

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Control Module References for scan tool information

1. Ignition OFF, disconnect the harness connector at the B39 A/C Evaporator Temperature Sensor.
2. Test for less than 5 Ω between the low reference circuit terminal B and ground.
• If greater than 5 Ω
1. Disconnect the harness connector at the K33 HVAC Control Module.
2. Test for less than 2 Ω in the low reference circuit end to end.
• If 2 Ω or greater, repair the open/high resistance in the circuit.
• If less than 2 Ω, replace the K33 HVAC Control Module.
• If less than 5 Ω
3. Ignition ON, turn the HVAC system ON.
4. Test for 4.8–5.2 V between the signal circuit terminal A and ground.
• If less than 4.8 V
1. Ignition OFF, disconnect the harness connector at the K33 HVAC Control Module.
2. Test for infinite resistance between the signal circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance
3. Test for less than 2 Ω in the signal circuit end to end.
• If 2 Ω or greater, repair the open/high resistance in the circuit.
• If less than 2 Ω, replace the K33 HVAC Control Module.
• If greater than 5.2 V
1. Ignition OFF, disconnect the harness connector at the K33 HVAC Control Module, ignition ON.
2. Test for less than 0.3 V between the signal circuit and ground.
• If greater than 0.3 V, repair the short to voltage on the circuit.
• If less than 0.3 V, replace the K33 HVAC Control Module.
• If within 4.8–5.2 V
5. Replace the B39 A/C Evaporator Temperature Sensor and verify the DTC does not reset.
• If DTC resets

  Replace the K33 HVAC Control Module.

• If DTC does not reset
6. All OK.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• HVAC Component Replacement Reference
• Control Module References for control module replacement, programming, and setup