B0173

DTC B0173 or B0178
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 B0173 02: Upper Left Duct Air Temperature Sensor Circuit Short to Ground

DTC B0173 05: Upper Left Duct Air Temperature Sensor Circuit Short to Battery or Open

DTC B0178 02: Lower Left Duct Air Temperature Sensor Circuit Short to Ground

DTC B0178 05: Lower Left Duct Air Temperature Sensor Circuit Short to Battery or Open

Diagnostic Fault Information





Circuit Description
The HVAC control module supplies the air temperature sensors with a low reference circuit and 5 V 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 air temperature sensor signal circuit is less than -36°C (-38°F) or more than 85°C (185°F) for more than 15 seconds.

Action Taken When the DTC Sets
A default value is used when the DTC is set.

Conditions for Clearing the DTC
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.

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
Vehicle in Service Mode, observe the Upper Left Duct Temperature Sensor parameter and the Lower Left Duct Temperature 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
Vehicle OFF, disconnect the harness connector at the appropriate B7 temperature sensor.
Vehicle OFF, test for less than 10 ohms between the low reference circuit terminal B 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 K33 HVAC control module.
Vehicle in Service Mode, verify the scan tool appropriate B7 temperature sensor parameter is less than -35°C (-39°F).
If greater than the specified range, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the K33 HVAC control module.
Install a 3 A fused jumper wire between the signal circuit terminal A and the low reference circuit terminal B. Verify the scan tool appropriate B7 Temperature sensor parameter is greater than 85°C (185°F).
If less than the specified range, test the signal circuit terminal A for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K33 HVAC control module.
If all circuits test normal, test or replace the appropriate B7 temperature sensor.

Component Testing
Test the air temperature sensor by varying the sensor temperature while monitoring the sensor resistance.
Compare the readings with the Sensor 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.

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