For 1990-2009 cars

### Diagnostic Instructions

• | 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.

### DTC Descriptors

DTC B0163 02: Passenger Compartment Temperature Sensor Circuit Short to Ground
DTC B0163 05: Passenger Compartment Temperature Sensor Circuit Short to Battery or Open
DTC B0173 02: Output Air Temperature Sensor 1 Circuit short to ground.
DTC B0173 05: Output Air Temperature Sensor 1 Circuit short to battery or open.
DTC B0178 02: Output Air Temperature Sensor 2 Circuit short to ground.
DTC B0178 05: Output Air Temperature Sensor 2 Circuit short to battery or open.

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Ambient Air Temperature Sensor Signal | B0158 02 | B0158 05 | B0158 05 | --
Inside Air Temperature Sensor Signal | B0163 02 | B0163 05 | B0163 05 | --
Upper Air Temperature Sensor Signal | B0173 02 | B0173 05 | B0173 05 | --
Lower Air Temperature Sensor Signal | B0178 02 | B0178 05 | B0178 05 | --
Left Sunload Sensor Signal | B0183 02 | B0183 05 | B0183 05 | --
Right Sunload Sensor Signal | B0188 02 | B0188 05 | B0188 05 | --
Evaporator Temperature Sensor Signal | B3933 02 | B3933 05 | B3933 05 | --
Low Reference | -- | B3933 05, B0158 05, B0163 05 | B3933 05, B0158 05, B0163 05 | --
Sunload sensors Ground Circuit | -- | B0183 05, B0188 05 | B0183 05, B0188 05 | --

### Circuit/System Description

#### Inside Air Temperature Sensor

The HVAC control module supplies the inside air temperature sensor with a low reference circuit and 5-volt 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 inside air temperature sensor refers to the passenger compartment.

#### Upper and Lower Air Duct Temperature Sensors

The HVAC control module supplies the air duct temperature sensors with a low reference circuit and 5-volt 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.

### Conditions for Running the DTC

The ignition is turned ON.

### Conditions for Setting the DTC

The HVAC control module detects the inside air temperature sensor signal circuit is less than -36°C (-38°F) or more than 215°C (419°F) for more than 15 seconds.

### Action Taken When the DTC Sets

The system operates using a default value.

### Conditions for Clearing the DTC

• | The DTC will become history if the HVAC control module no longer detects the condition that set the DTC.

• | The history DTC will clear after 50 fault-free ignition cycles.

### Reference Information

#### Schematic Reference

HVAC Schematics

#### Connector End View Reference

HVAC Connector End Views

#### Description and Operation

Air Temperature Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for Scan Tool Information

### Circuit/System Verification

Ignition ON, observe the scan tool Inside Air Temperature Sensor or appropriate air duct temperature sensor actual temperature parameter. The reading should be between -35°C (-39°F) and 98°C (208°F) and change with inside passenger compartment or upper or lower air duct air temperature changes.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the inside air temperature sensor or appropriate air duct temperature sensor.
2. Ignition OFF, test for less than 10 ohms of resistance between the low reference circuit terminal B of the inside air temperature sensor and terminal 2 of the upper and lower air temperature sensors and ground.

⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the HVAC control module.

3. Ignition ON, verify that both the scan tool Inside Air Temperature Sensor and Heater and A/C air duct temperature sensor actual temperature parameters are less than -35°C (-39°F).

⇒ | If greater than the specified range, test the signal circuit terminal A for the IAT sensor or terminal 1 for the upper and lower air temperature sensors for a short to ground. If the circuit tests normal, replace the HVAC control module.

4. Install a 3A fused jumper wire between the inside air temperature signal circuit terminal A and the low reference circuit terminal B. Verify the scan tool Inside Air Temperature Sensor parameter is greater than 98°C (208°F). Install a 3A fused jumper wire between the upper and lower air duct temperature signal circuit terminal 1 and the low reference circuit terminal 2. Verify the scan tool Inside Air Temperature Sensor and Upper (A/C) and Lower (Heater) parameters are greater than 98°C (208°F).

⇒ | If less than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.

5. If all circuits test normal, test or replace the inside air temperature or appropriate upper or lower air duct temperature sensor.

### Component Testing

Important: Sensor Resistance Table for this test. A thermometer can be used to test the sensor off the vehicle in warn and or cold water.

1. Test the inside air temperature sensor or upper and lower air duct temperature sensor by varying the sensor temperature while monitoring the sensor resistance.
2. Compare the readings with the Temperature VS Resistance table and verify that the resistance is within 5 percent of the specification.

⇒ | If not within the specified range, replace the sensor.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Inside Air Temperature Sensor Replacement

• | Duct Air Temperature Sensor Replacement - Upper

• | Duct Air Temperature Sensor Replacement - Lower

• | Control Module References for HVAC control module replacement, setup and programming