B0159 - Outside Air Temperature Sensor Circuit Range/Performance

Introduction:

The B0159 diagnostic trouble code (DTC) indicates an issue with the Outside Air Temperature (OAT) sensor circuit. This sensor plays a crucial role in various vehicle systems, affecting everything from climate control to engine performance. Understanding the causes, symptoms, and potential solutions for this code is essential for maintaining optimal vehicle operation and addressing potential discomfort or inefficiencies.

Table: B0159 - Outside Air Temperature Sensor Circuit Range/Performance

Detailed Explanations:

Definition of B0159: This code signifies that the vehicle's computer (PCM) has detected that the signal received from the outside air temperature sensor is outside the expected range. This could mean the signal is either too high (indicating a very cold temperature when it isn't) or too low (indicating a very warm temperature when it isn't) or erratic. The PCM uses this sensor data to adjust various systems, and an inaccurate reading can lead to problems.

Common Symptoms: The most obvious symptom is an inaccurate outside air temperature display on the dashboard. The automatic climate control system may malfunction, struggling to maintain the desired cabin temperature. In some vehicles, a B0159 code can lead to reduced engine performance, although this is less common. The engine cooling fan operation might be faulty, running unnecessarily or not running when needed. Finally, you might experience poor fuel economy due to incorrect engine adjustments based on the faulty temperature reading.

Potential Causes: A faulty OAT sensor is a primary suspect. Open or shorted wiring in the sensor circuit can disrupt the signal. Corroded connectors can also cause intermittent or inaccurate readings. In rare cases, the PCM itself might be faulty. Incorrect sensor installation (if recently replaced) can also be a cause. Environmental factors like extreme temperatures or moisture can sometimes affect sensor performance. Sensor overload due to extreme conditions might trigger the code. Finally, high resistance in the circuit due to damaged wiring can also trigger this DTC.

Diagnostic Steps: Start with a visual inspection of the sensor and its wiring, looking for damage or corrosion. Use a scan tool to read the DTC and view live data from the OAT sensor. Consult a wiring diagram for your specific vehicle to understand the sensor circuit. Perform a sensor test using a multimeter to check its resistance at different temperatures. In some cases, PCM testing may be necessary. Use a multimeter to perform resistance testing, voltage testing and continuity testing of the sensor circuit.

Troubleshooting Tools: You'll need a scan tool to read the DTC. A multimeter is essential for testing the sensor and wiring. Refer to a wiring diagram for your specific vehicle. Connector cleaning tools can help remove corrosion. A replacement OAT sensor will be needed if the sensor is faulty. Wire strippers, crimpers, and a soldering iron (if needed) will be required for wiring repairs.

Impact on Vehicle Systems: The B0159 code primarily affects the automatic climate control system, preventing it from maintaining the desired cabin temperature. It can also influence the engine control system, as the PCM uses OAT data for fuel mixture adjustments. The fuel management system can be indirectly affected, leading to reduced fuel economy. Finally, the cooling system might be affected, with the engine cooling fan potentially operating incorrectly.

Related Diagnostic Trouble Codes: You might see other temperature sensor codes, such as those related to the intake air temperature (IAT) sensor. Climate control system codes might also appear, indicating problems with the AC compressor or other components. In rare cases, PCM-related codes might be present, suggesting a more serious issue.

Sensor Location (General): The OAT sensor is typically located in the front of the vehicle to get an accurate reading of the outside air temperature. Common locations include behind the grille, near the radiator support, in the bumper, or underneath the side mirror.

Sensor Function: The OAT sensor measures the temperature of the air outside the vehicle. This data is sent to the PCM, which uses it to adjust various systems, including the climate control system and the engine's fuel mixture.

Sensor Type: The OAT sensor is typically a thermistor-based sensor. A thermistor is a type of resistor whose resistance changes with temperature. The PCM measures the resistance of the thermistor to determine the outside air temperature.

Frequency of Occurrence: The B0159 code is moderately common, but its frequency depends on the vehicle make, model, age, and environmental conditions. Vehicles exposed to harsh weather conditions are more likely to experience sensor or wiring issues.

Severity of the Issue: The severity of the B0159 code is generally low to moderate. While it primarily affects comfort and efficiency, it can potentially impact engine performance in extreme cases. Ignoring the code can lead to discomfort and reduced fuel economy.

Expected Resistance Values: The expected resistance values of the OAT sensor vary depending on the manufacturer and the temperature. You'll need to consult vehicle-specific repair information for exact values. For example, at 20°C (68°F), a typical value might be 2000-3000 Ohms.

Expected Voltage Values: Similarly, the expected voltage values vary by manufacturer. Typically, the sensor receives a 5V reference voltage, and the signal voltage changes based on resistance. Consult vehicle-specific repair information for exact values.

Impact on Automatic Climate Control: The B0159 code can cause incorrect or inconsistent temperature readings in the automatic climate control system. This can lead to the inability to maintain the desired cabin temperature, and the system might switch to default settings. In some cases, it can even cause compressor issues.

Impact on Engine Performance: The B0159 code can lead to minor adjustments to the fuel mixture in some cases. This can result in reduced fuel efficiency. In some vehicles, it can also affect the engine cooling fan operation.

Impact on Fuel Economy: Because the PCM uses the OAT sensor reading to make adjustments to the fuel mixture, an inaccurate reading can lead to a slight reduction in fuel economy.

Preventative Measures: Regular vehicle maintenance is key to preventing the B0159 code. Carefully inspect the wiring and connectors for damage or corrosion. Avoid pressure washing directly on sensors. Promptly address any warning signs of climate control or engine performance issues.

Repair Costs (Estimate): The cost to repair the B0159 issue can range from $50 to $300, depending on the cause. Sensor replacement is generally inexpensive, while wiring repairs or PCM issues can be more costly.

DIY Difficulty Level: The DIY difficulty level is low to medium. Sensor replacement is typically straightforward, but diagnosing wiring issues requires more technical knowledge and experience.

PCM Learning/Adaptation: In some cases, the PCM needs to relearn or adapt after the OAT sensor is replaced. Clearing the DTC and allowing the system to recalibrate itself is often recommended. Some vehicles may require a specific PCM relearn procedure using a scan tool.

Sensor Calibration: OAT sensors are pre-calibrated and do not require additional calibration after replacement.

Connector Pinout Information: The connector pinout information varies by manufacturer. Consult vehicle-specific repair information for exact pinout details. Typically, it includes a power/reference voltage wire and a signal wire.

Common Sensor Brands: Common brands of OAT sensors include Bosch, Delphi, Denso, Standard Motor Products, and Walker Products.

Effect of Extreme Temperatures: Extreme heat or cold can temporarily affect sensor readings, potentially triggering the code. Pre-existing wiring or connector issues can be exacerbated by temperature fluctuations.

Impact of Aftermarket Accessories: Incorrect wiring or interference with the sensor circuit from aftermarket accessories can cause the code to appear. Poorly installed aftermarket electronics can create electrical noise that disrupts sensor readings.

Frequently Asked Questions:

• What does the B0159 code mean? It means the outside air temperature sensor signal is out of range or performing poorly.

• Can I drive with a B0159 code? Yes, but your climate control may not work correctly, and fuel economy might be slightly affected.

• How do I fix a B0159 code? Start by inspecting the sensor and wiring; consider replacing the sensor if it's faulty.

• Is the OAT sensor expensive to replace? Generally, OAT sensors are relatively inexpensive to replace.

• Will a bad OAT sensor affect my engine? It can slightly affect engine performance and fuel economy, but usually not significantly.

Conclusion:

The B0159 code indicates a problem with the outside air temperature sensor circuit. Addressing this issue promptly will ensure proper climate control function and prevent potential impacts on engine performance and fuel economy.