The B0179 diagnostic trouble code (DTC) indicates a problem with the Output Air Temperature (OAT) Sensor #2, specifically the "Lower," "Single," or "LH" sensor. This sensor plays a crucial role in the automatic climate control (ACC) system, helping to regulate cabin temperature. A faulty sensor or circuit can lead to inaccurate temperature readings, resulting in uncomfortable cabin conditions and potential damage to the HVAC system.
Comprehensive Information Table
| Category | Description | Possible Causes |
|---|---|---|
| Sensor Function | Measures the temperature of the air exiting the HVAC system after it has passed through the evaporator core. Used by the ACC system to control blower speed, vent position, and compressor operation. | N/A |
| Location | Typically located in the ductwork near the floor on the driver's or passenger's side of the vehicle, often near the evaporator core housing. The exact location varies by vehicle make and model. | N/A |
| Circuit Components | Sensor, wiring harness, connectors, and the HVAC control module (also known as the climate control module or body control module). | N/A |
| Typical Resistance Range | Varies by manufacturer and sensor type, but generally ranges from a few hundred ohms at high temperatures to several thousand ohms at low temperatures. Consult the vehicle's service manual for specific values. | N/A |
| Voltage Range | Usually operates on a 5-volt reference signal. The voltage reading changes based on temperature; lower temperatures result in higher voltage readings, and vice versa. | N/A |
| Symptoms | Inaccurate cabin temperature, inconsistent blower speed, HVAC system blowing hot or cold air regardless of settings, delayed or no response to temperature adjustments, ACC system malfunction. | N/A |
| Common Causes of B0179 | Faulty sensor, open or shorted wiring, corroded connectors, poor electrical connections, damaged wiring harness, faulty HVAC control module. | N/A |
| Diagnostic Steps | Visual inspection of the sensor and wiring, check for voltage and ground at the sensor connector, measure sensor resistance, scan for other DTCs, perform a wiggle test on the wiring harness. | N/A |
| Tools Required | Multimeter, scan tool, wiring diagrams, basic hand tools. | N/A |
| Related DTCs | B017A, B017B, B017C, other OAT sensor codes, HVAC system malfunction codes. | N/A |
| Repair Procedures | Replace the sensor, repair or replace damaged wiring, clean or replace corroded connectors, replace the HVAC control module (if necessary, after confirming other potential causes). | N/A |
| Sensor Types | Thermistor-based sensors are the most common type. | N/A |
| Impact on Vehicle Operation | Primarily affects the comfort and efficiency of the HVAC system. May also indirectly affect fuel economy if the ACC system is constantly working to compensate for inaccurate temperature readings. | N/A |
| "Lower," "Single," or "LH" | These designations indicate the specific sensor being monitored. "Lower" typically refers to a sensor located lower in the ductwork, while "Single" may indicate only one sensor is present. "LH" designates the sensor on the left-hand side of the vehicle. | N/A |
| Circuit Range/Performance | Indicates that the signal from the sensor is outside of the expected range or is not performing as expected. This could be due to a faulty sensor, wiring issues, or a problem with the HVAC control module. | N/A |
| Testing with a Scan Tool | A scan tool can display the live data stream from the sensor, allowing you to monitor its temperature readings and voltage output. This can help you determine if the sensor is functioning correctly. | N/A |
| Testing with a Multimeter | A multimeter can be used to measure the sensor's resistance and voltage. This can help you identify open circuits, short circuits, and faulty sensors. | N/A |
| Data Stream Analysis | Compare the OAT sensor readings with other temperature sensors in the vehicle (e.g., ambient temperature sensor, engine coolant temperature sensor) to identify any discrepancies. | N/A |
| Wiring Diagram Importance | Crucial for identifying the correct wires to test and for understanding the circuit layout. Always consult the vehicle's service manual for accurate wiring diagrams. | N/A |
| Connector Inspection | Carefully inspect the sensor connector for corrosion, damage, and loose connections. Clean or replace the connector as needed. | N/A |
| Wiring Harness Inspection | Inspect the wiring harness for any signs of damage, such as cuts, abrasions, or melted insulation. Repair or replace the harness as needed. | N/A |
| HVAC Control Module Check | If all other components check out, the HVAC control module may be faulty. However, this should be the last thing to consider since it is the most costly item to replace. It is necessary to rule out all other possibilities first. | N/A |
Detailed Explanations
Sensor Function: The Output Air Temperature (OAT) sensor #2 measures the temperature of the air leaving the HVAC system. This data is essential for the ACC system to accurately regulate cabin temperature. The system uses this reading to adjust blower speed, vent positions, and compressor operation to maintain the desired temperature.
Location: The "Lower," "Single," or "LH" designation helps pinpoint the sensor's location. It's usually found in the ductwork, often near the evaporator core housing. "Lower" suggests a position low in the ductwork, while "Single" means it's the only sensor in that location. "LH" denotes the sensor on the left-hand (driver's) side. Precise location requires consulting the vehicle's service manual.
Circuit Components: The circuit consists of the OAT sensor itself, the wiring harness that connects the sensor to the HVAC control module, connectors that provide electrical connections, and finally, the HVAC control module (also known as the climate control module or body control module). Each of these components must be functioning correctly for the circuit to operate properly.
Typical Resistance Range: The resistance of the sensor varies with temperature. At higher temperatures, the resistance is lower, and at lower temperatures, the resistance is higher. Consult the vehicle's service manual for the specific resistance values for the OAT sensor at different temperatures. This is crucial for accurate diagnosis.
Voltage Range: OAT sensors typically operate on a 5-volt reference signal. The voltage output changes depending on the temperature. Lower temperatures will result in higher voltage readings, and higher temperatures will result in lower voltage readings. This inverse relationship is important to remember when diagnosing the circuit.
Symptoms: Common symptoms of a B0179 code include inaccurate cabin temperature, inconsistent blower speed, the HVAC system blowing hot or cold air regardless of the settings, a delayed or absent response to temperature adjustments, and overall ACC system malfunction. These symptoms indicate that the system is not receiving accurate temperature data.
Common Causes of B0179: The most common causes of a B0179 code are a faulty sensor, open or shorted wiring, corroded connectors, poor electrical connections, a damaged wiring harness, or a faulty HVAC control module. A thorough inspection is required to pinpoint the exact cause.
Diagnostic Steps: The diagnostic process includes a visual inspection of the sensor and wiring, checking for voltage and ground at the sensor connector, measuring sensor resistance, scanning for other DTCs, and performing a wiggle test on the wiring harness to identify intermittent issues. A systematic approach is essential for accurate diagnosis.
Tools Required: You'll need a multimeter for measuring voltage and resistance, a scan tool for reading DTCs and live data, wiring diagrams for identifying circuit components, and basic hand tools for accessing and disconnecting components.
Related DTCs: Related DTCs may include B017A, B017B, B017C, other OAT sensor codes, and HVAC system malfunction codes. These codes can provide additional clues about the underlying problem.
Repair Procedures: Repair procedures may involve replacing the sensor, repairing or replacing damaged wiring, cleaning or replacing corroded connectors, or, in rare cases, replacing the HVAC control module. Always follow the manufacturer's recommendations for repair procedures.
Sensor Types: Most OAT sensors are thermistor-based sensors. These sensors change their resistance in response to temperature changes.
Impact on Vehicle Operation: The primary impact is on the comfort and efficiency of the HVAC system. Inaccurate temperature readings can cause the system to work harder than necessary, potentially affecting fuel economy.
"Lower," "Single," or "LH": These designations are important for identifying the specific sensor that is causing the problem. "Lower" usually refers to a sensor positioned lower in the ductwork. "Single" indicates that there is only one sensor in that location. "LH" indicates the sensor located on the left-hand side of the vehicle.
Circuit Range/Performance: The "Circuit Range/Performance" aspect of the code indicates that the signal from the sensor is outside the expected range or not performing as it should. This could be due to a faulty sensor, wiring problems, or a problem with the HVAC control module.
Testing with a Scan Tool: A scan tool can display live data from the sensor, allowing you to monitor its temperature readings and voltage output. This is a valuable tool for determining if the sensor is functioning correctly and providing accurate data.
Testing with a Multimeter: A multimeter can be used to measure the sensor's resistance and voltage. This can help you identify open circuits, short circuits, and faulty sensors.
Data Stream Analysis: Compare the OAT sensor readings with other temperature sensors in the vehicle (e.g., ambient temperature sensor, engine coolant temperature sensor) to identify any discrepancies. Inconsistencies can indicate a faulty sensor or circuit.
Wiring Diagram Importance: Wiring diagrams are essential for identifying the correct wires to test and for understanding the circuit layout. Always consult the vehicle's service manual for accurate wiring diagrams.
Connector Inspection: Carefully inspect the sensor connector for corrosion, damage, and loose connections. Clean or replace the connector as needed to ensure a good electrical connection.
Wiring Harness Inspection: Inspect the wiring harness for any signs of damage, such as cuts, abrasions, or melted insulation. Repair or replace the harness as needed.
HVAC Control Module Check: If all other components check out, the HVAC control module may be faulty. However, this should be the last thing to consider since it is the most costly item to replace. It is necessary to rule out all other possibilities first.
Frequently Asked Questions
What does the B0179 code mean? The B0179 code indicates a problem with the Output Air Temperature Sensor #2 (Lower; Single or LH) circuit range or performance. This means the sensor signal is not within the expected parameters.
What are the symptoms of a B0179 code? Common symptoms include inaccurate cabin temperature, inconsistent blower speed, and the HVAC system blowing hot or cold air regardless of settings. The ACC system may also malfunction.
Can I fix the B0179 code myself? Depending on your mechanical skills, you may be able to diagnose and repair the issue. Start with a visual inspection and basic circuit testing before considering more complex repairs.
How do I test the OAT sensor? Use a multimeter to measure the sensor's resistance and voltage. Compare the readings to the specifications in the vehicle's service manual.
What if replacing the sensor doesn't fix the problem? If replacing the sensor doesn't resolve the issue, check the wiring harness, connectors, and HVAC control module for damage or faults. A thorough diagnostic process is essential.
Conclusion
The B0179 code signifies a problem with the Output Air Temperature Sensor #2 circuit, impacting the HVAC system's performance. A systematic approach to diagnosis, including visual inspection, circuit testing, and data stream analysis, is crucial for accurate repair and restoring the comfort of your vehicle's climate control.