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 Descriptor

DTC B0173 02: Upper Left Outlet Air Temperature Sensor Circuit Short to Ground
DTC B0173 05: Upper Left Outlet Air Temperature Sensor Circuit Short to Battery or Open
DTC B0178 02: Lower Left Outlet Air Temperature Sensor Circuit Short to Ground
DTC B0178 05: Lower Left Outlet Air Temperature Sensor Circuit Short to Battery or Open
DTC B0509 02: Upper Right Outlet Air Temperature Sensor Circuit Short to Ground
DTC B0509 05: Upper Right Outlet Air Temperature Sensor Circuit Short to Battery or Open
DTC B0514 02: Lower Right Outlet Air Temperature Sensor Circuit Short to Ground
DTC B0514 05: Lower Right Outlet Air Temperature Sensor Circuit Short to Battery or Open
DTC B3933 02: Air Conditioning Evaporator Temperature Sensor Circuit Short to Ground
DTC B3933 05: Air Conditioning Evaporator Temperature Sensor Circuit Short to Battery or Open

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Upper Left Outlet Air Temperature Sensor Signal | B0173 02 | B0173 05 | B0173 05 | 1
Upper Left Outlet Air Temperature Low Reference | -- | B0173 05 | B0173 05, B0178 05, B0509 05, B0514 05, B3933 05 | --
Upper Right Outlet Air Temperature Sensor Signal | B0509 02 | B0509 05 | B0509 05 | 1
Upper Right Outlet Air Temperature Low Reference | -- | B0509 05 | B0173 05, B0178 05, B0509 05, B0514 05, B3933 05 | --
Lower Left Outlet Air Temperature Sensor Signal | B0178 02 | B0178 05 | B0178 05 | 1
Lower Left Outlet Air Temperature Sensor Low Reference | -- | B0178 05 | B0173 05, B0178 05, B0509 05, B0514 05, B3933 05 | --
Lower Right Outlet Air Temperature Sensor Signal | B0514 02 | B0514 05 | B0514 05 | 1
Lower Right Outlet Air Temperature Sensor Low Reference | -- | B0514 05 | B0173 05, B0178 05, B0509 05, B0514 05, B3933 05 | --
Evaporator Temperature Sensor Signal | B3933 02 | B3933 05 | B3933 05 | 1
Evaporator Temperature Sensor Low Reference | -- | B3933 05 | B0173 05, B0178 05, B0509 05, B0514 05, B3933 05 | --
1. Air Temperature Malfunction

### Circuit/System Description

The air temperature sensors are a 2-wire negative temperature co-efficient thermistor. The vehicle uses the following air temperature sensors:

• | Air temperature sensor - left upper

• | Air temperature sensor - left lower

• | Air temperature sensor - right upper

• | Air temperature sensor - right lower

• | Evaporator temperature sensor

A signal and low reference circuit enables the sensor to operate. As the air temperature surrounding the sensor increases, the sensor resistance decreases. The sensor signal voltage decreases as the resistance decreases. The sensor operates within a temperature range between -40 to +85°C (-40 to +185°F). The sensor signal varies between 0-5 V. The HVAC control module converts the signal to a range between 0-255 counts. As the air temperature increases the count value will decrease. If the HVAC control module detects a malfunctioning sensor, then the control module software will use a default air temperature value. The default action ensures that the HVAC system can adjust the inside air temperature near the desired temperature until the condition is corrected.

### Conditions for Running the DTC

• | Ignition ON.

• | The HVAC control module is ON.

### Conditions for Setting the DTC

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.

### Action Taken When the DTC Sets

The system operates using a default value.

### Conditions for Clearing the DTC

The sensor signal is within specified range between 0.1 V and 4.9 V.

### Reference Information

#### Schematic Reference

HVAC Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Automatic HVAC 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

1. Verify that no DTC is present.

⇒ | If a DTC is present, refer to Circuit/System Testing.

2. Measure actual temperature using a thermometer at each of the duct temperature sensors. Compare this value to the appropriate scan tool Duct Actual parameter. The measured temperature should be within 5°C (9°F) difference of appropriate Duct Actual parameter value.

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

3. Measure actual evaporator temperature using a thermometer. Compare this value to the scan tool A/C Evaporator Temperature Sensor parameter. The measured temperature should be within 5°C (9°F) difference of parameter value.

⇒ | If not within the specified range, replace the B39 Evaporator Temperature Sensor.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the appropriate temperature sensor.
2. Test for less than 5 Ω between the temperature sensor ground circuit terminal 1 and ground.

⇒ | If greater than the specified value, test the ground circuit for an open/high resistance.

3. Ignition ON, test for 4.8-5.2 V between the signal circuit terminal 2 and ground.

⇒ | If less than the specified range, test the signal circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the K33 HVAC Control Module.

⇒ | If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the K33 HVAC Control Module.

4. If all circuits test normal, replace the temperature sensor and verify the DTC does not reset.

⇒ | If the DTC resets, replace the K33 HVAC Control Module.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Duct Air Temperature Sensor Replacement - Upper Left Side

• | Duct Air Temperature Sensor Replacement - Lower Left Side

• | Duct Air Temperature Sensor Replacement - Upper Right Side

• | Duct Air Temperature Sensor Replacement - Lower Right Side

• | LINK 63453

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