For 1990-2009 cars

## DTC B0158 or B0168 Current

### 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 B0158 03: Outside Air Temperature Sensor Circuit Voltage Below Threshold
DTC B0158 07: Outside Air Temperature Sensor Circuit Voltage Above Threshold
DTC B0168 03: Passenger Compartment Temperature Sensor Voltage Below Threshold
DTC B0168 07: Passenger Compartment Temperature Sensor Voltage Above Threshold

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Ambient Air Temperature Sensor Circuit | B0158 03 | B0158 07 | B0158 07 | --
Inside Air Temperature Sensor Circuit | B0168 03 | B0168 07 | B0158 07 | --

### Circuit Description

The HVAC control module monitors the air temperature sensors with a low reference circuit and 5-volt signal circuit. The HVAC control module monitors the voltage drop across the sensor. When the ambient air temperatures are cold, the resistance of the sensor is high and the voltage signals are high. When the ambient air temperatures are hot, the resistance of the sensors is low and the voltage signals are low.

### Conditions for Running the DTC

The ignition is ON.

### Conditions for Setting the DTC

• | The HVAC control module detects the sensor signal circuit is less than -35°C (-39°F).

• | The HVAC control module detects the sensor signal circuit is greater than 85°C (185°F).

### Action Taken When the DTC Sets

#### B0158

• | The DIC display will display "-" for outside air temperature.

• | The system operates using a default value.

• | A warning will display on the Driver Information Center (DIC) "Service Air Conditioning System ".

#### B0168

• | The system operates using a default value.

• | A warning will display on the Driver Information Center (DIC) "Service Air Conditioning System ".

### Conditions for Clearing the DTC

• | The condition for setting the DTC is no longer present.

• | The HVAC control module automatically clears the history DTC when a current DTC is not detected in 50 fault-free ignition cycles.

• | The DTC can be cleared using a scan tool.

### Reference Information

#### Schematic Reference

HVAC Schematics

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References

### Circuit/System Verification

Ignition ON, observe the appropriate scan tool Air Temp Sensor parameter. The reading should be between -35°C (-39°F) and 85°C (185°F) and change with air temperature changes.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the appropriate air temperature sensor.
2. Ignition OFF, test for less than 10 ohms between the following low reference circuit terminal and ground.

• | Outside air temperature sensor terminal A

• | Inside air temperature sensor terminal B

⇒ | 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 the appropriate scan tool Air Temp Sensor parameter is less than -35°C (-39°F).

⇒ | If greater than the specified range, test the following signal circuit terminal for a short to ground. If the circuit tests normal, replace the HVAC control module.

• | Outside air temperature sensor terminal B

• | Inside air temperature sensor terminal A

4. Install a 3A fused jumper wire between the following signal circuit terminal and the low reference circuit terminal. Verify the scan tool Air Temp Sensor parameter is greater than 85°C (185°F).

• | Inside air temperature sensor terminal Aand B.

• | Ambient temperature sensor terminal B and A.

⇒ | 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 air temperature sensor.

### Component Testing

Ignition OFF, remove the appropriate temperature sensor and perform a resistance test across the sensor terminals. Verify that the resistance readings correspond with those in the sensor resistance tables. If outside of the specified range, replace the appropriate sensor.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Ambient Air Temperature Sensor Replacement

• | Inside Air Temperature Sensor Replacement

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