Introduction
The B1255 diagnostic trouble code (DTC) signals a problem within the external air temperature sensor circuit of a vehicle's climate control system. This sensor, often called the ambient temperature sensor, plays a crucial role in providing accurate temperature readings to the vehicle's computer. This information is used to optimize the performance of the air conditioning and heating systems, ensuring passenger comfort and efficient operation. When the system detects an open circuit in the sensor wiring or the sensor itself, the B1255 code is triggered.
A malfunctioning external temperature sensor can lead to inaccurate temperature displays, inefficient climate control performance, and potentially even affect other vehicle systems that rely on ambient temperature data. Therefore, understanding the causes, symptoms, and troubleshooting steps associated with the B1255 code is essential for proper vehicle maintenance and repair.
Comprehensive Information Table
| Topic | Description | Possible Causes |
|---|---|---|
| Sensor Function | Measures the outside air temperature and relays this information to the vehicle's climate control system and often the engine control unit (ECU). This data is used to adjust heating, cooling, and potentially fuel mixture. | N/A |
| Circuit Definition | The electrical path connecting the external temperature sensor to the vehicle's computer. This includes the sensor itself, wiring, connectors, and any related control modules. An "open" circuit means there is a break in this path, preventing electrical flow. | Damaged wiring: Corrosion, breaks, or shorts in the wiring harness leading to the sensor. |
| Faulty sensor: The sensor itself may be internally damaged or malfunctioning. | ||
| Loose or corroded connectors: Connectors connecting the sensor to the wiring harness may be loose, corroded, or damaged. | ||
| Open circuit in the ECM/BCM: Rarely, the issue could lie within the Engine Control Module (ECM) or Body Control Module (BCM), which process the sensor data. | ||
| Symptoms | Noticeable signs that the B1255 code is present. | Inaccurate Temperature Display: The outside temperature display on the dashboard may show an incorrect reading (often very high or very low). |
| Malfunctioning Climate Control: The air conditioning or heating system may not function correctly, blowing hot air when it should be cold or vice versa. This can also result in intermittent or erratic temperature control. | ||
| Check Engine Light: The check engine light may illuminate on the dashboard. | ||
| Possible Impact on Fuel Economy: While less common, inaccurate temperature readings could potentially affect fuel economy in some vehicles if the ECU uses the sensor data for fuel mixture adjustments. | ||
| Diagnostic Tools | Equipment needed to diagnose the B1255 code. | OBD-II Scanner: To read and clear the diagnostic trouble code. |
| Multimeter: To test the continuity and voltage of the sensor and wiring. | ||
| Wiring Diagram: To understand the circuit layout and identify the correct wires to test. | ||
| Troubleshooting Steps | A logical process to identify and resolve the underlying cause of the B1255 code. | Visual Inspection: Carefully inspect the sensor, wiring, and connectors for any signs of damage, corrosion, or looseness. |
| Sensor Resistance Test: Use a multimeter to measure the resistance of the sensor. Compare the reading to the manufacturer's specifications. An open circuit indicates a faulty sensor. | ||
| Wiring Continuity Test: Use a multimeter to check for continuity in the wiring harness between the sensor and the vehicle's computer. An open circuit indicates a break in the wiring. | ||
| Voltage Test: Check for the correct voltage at the sensor connector. Refer to the vehicle's wiring diagram for the correct voltage specifications. | ||
| Connector Inspection and Cleaning: Clean and tighten any loose or corroded connectors. Apply dielectric grease to protect the connections. | ||
| Sensor Location | Where the external air temperature sensor is typically found on a vehicle. | Behind the front grille: This is a common location, allowing the sensor to be exposed to outside air. |
| Under the side mirror: Some vehicles mount the sensor under one of the side mirrors. | ||
| Near the front bumper: Another possible location, often in a protected area. | ||
| Related Codes | Other DTCs that may appear alongside B1255. | B1256: Air Temperature External Sensor Circuit Short To Ground. |
| B1257: Air Temperature External Sensor Circuit Short To Battery. | ||
| Codes related to the climate control system's performance. These codes may indicate issues with the compressor, blower motor, or other components. | ||
| Sensor Replacement | Steps involved in replacing a faulty external temperature sensor. | Disconnect the negative battery terminal: To prevent electrical shorts. |
| Locate the sensor: Refer to the vehicle's service manual or wiring diagram. | ||
| Disconnect the sensor connector: Carefully disconnect the electrical connector from the sensor. | ||
| Remove the sensor: Unscrew or unclip the sensor from its mounting location. | ||
| Install the new sensor: Connect the electrical connector to the new sensor and secure it in its mounting location. | ||
| Reconnect the negative battery terminal: Reconnect the negative battery terminal and clear the DTC. |
Detailed Explanations
Sensor Function: The external air temperature sensor is a thermistor, a type of resistor whose resistance changes with temperature. The vehicle's computer sends a reference voltage to the sensor, and the sensor's resistance affects the voltage that is returned to the computer. By measuring this voltage, the computer can accurately determine the outside air temperature. This information is then used by the climate control system to regulate the heating and cooling functions, and in some vehicles, it may also be used by the engine control unit (ECU) to optimize fuel mixture.
Circuit Definition: The "circuit" refers to the complete electrical path that allows the sensor to communicate with the vehicle's computer. This path includes the sensor itself, the wiring harness connecting the sensor to the computer, the connectors that join the wires, and the internal circuitry within the computer that processes the sensor data. An "open" circuit means there's a break in this path, preventing the flow of electricity. This break could be due to a broken wire, a loose connector, or a faulty sensor.
Symptoms: The symptoms of a B1255 code can vary depending on the vehicle and the severity of the problem. A common symptom is an inaccurate temperature display on the dashboard, which might show a consistently high or low temperature, or an erratic reading. The climate control system may malfunction, blowing hot air when it should be cold, or vice versa. The check engine light is often illuminated. In some cases, an inaccurate temperature reading could potentially affect fuel economy, although this is less common.
Diagnostic Tools: Diagnosing a B1255 code requires a few key tools. An OBD-II scanner is essential for reading and clearing the diagnostic trouble code. A multimeter is used to test the continuity and voltage of the sensor and wiring, helping to pinpoint the location of the open circuit. A wiring diagram is invaluable for understanding the circuit layout and identifying the correct wires to test.
Troubleshooting Steps: A systematic approach is crucial for troubleshooting a B1255 code. Begin with a visual inspection of the sensor, wiring, and connectors for any signs of damage, corrosion, or looseness. Next, perform a sensor resistance test using a multimeter. Compare the reading to the manufacturer's specifications; an open circuit indicates a faulty sensor. Then, conduct a wiring continuity test to check for breaks in the wiring harness. Finally, check for the correct voltage at the sensor connector. Inspect and clean any loose or corroded connectors.
Sensor Location: The location of the external air temperature sensor can vary depending on the vehicle manufacturer and model. Common locations include behind the front grille, under the side mirror, or near the front bumper. Consulting the vehicle's service manual is the best way to determine the exact location of the sensor.
Related Codes: The B1255 code is often accompanied by other related codes. B1256 indicates a short to ground in the external air temperature sensor circuit, while B1257 indicates a short to battery. Other codes related to the climate control system's performance, such as codes related to the compressor or blower motor, may also be present.
Sensor Replacement: Replacing a faulty external temperature sensor is typically a straightforward process. First, disconnect the negative battery terminal to prevent electrical shorts. Then, locate the sensor and disconnect the sensor connector. Remove the sensor and install the new sensor, connecting the electrical connector and securing it in place. Finally, reconnect the negative battery terminal and clear the DTC.
Frequently Asked Questions
What does the B1255 code mean? The B1255 code indicates an open circuit in the external air temperature sensor circuit. This means there's a break in the electrical path between the sensor and the vehicle's computer.
Can I still drive my car with a B1255 code? Yes, you can usually still drive your car, but the climate control system may not function correctly. The inaccurate temperature reading could also potentially affect other vehicle systems.
How much does it cost to fix a B1255 code? The cost to fix a B1255 code can vary depending on the cause. Replacing the sensor is usually relatively inexpensive, while repairing damaged wiring can be more costly.
Where is the external temperature sensor located? The sensor is typically located behind the front grille, under the side mirror, or near the front bumper. Consult your vehicle's service manual for the exact location.
Can I fix the B1255 code myself? Yes, if you have basic mechanical skills and the necessary tools, you can often diagnose and repair the B1255 code yourself. However, if you're not comfortable working on your vehicle, it's best to take it to a qualified mechanic.
Conclusion
The B1255 code signifies an open circuit in the external air temperature sensor circuit, leading to potential climate control malfunctions and inaccurate temperature readings. By understanding the causes, symptoms, and troubleshooting steps outlined in this article, you can effectively diagnose and resolve the issue, ensuring the proper functioning of your vehicle's climate control system. Thoroughly inspect the wiring and sensor before replacing any parts to avoid unnecessary expenses.