B1251 – Air Temperature Internal Sensor Circuit Open

The ODBII code B1251 indicates that there is an open circuit in the air temperature internal sensor, which means the sensor is not providing a proper signal to the vehicle’s control module.

The severity of ODBII code B1251 is moderate.

Common Causes For: B1250 Air Temperature Internal Sensor Circuit Failure

• Faulty air temperature sensor
• Open or damaged wiring in the sensor circuit
• Poor electrical connections or corroded terminals
• Short circuit in the wiring
• Faulty engine control module (ECM) or powertrain control module (PCM)

Common misdiagnosis for B1251 Air Temperature Internal Sensor Circuit Open

• Faulty air temperature sensor
• Wiring issues or shorts in the circuit
• Faulty engine control module (ECM)
• Incorrectly diagnosed as a coolant temperature sensor issue
• Misinterpretation as a cabin temperature sensor problem
• Air conditioning system faults
• Issues with the vehicle’s HVAC system
• Battery or charging system problems affecting sensor readings

Common Troubleshooting Steps

When dealing with an OBD-II code B1251, which indicates an “Air Temperature Internal Sensor Circuit Open,” there are several common troubleshooting steps you can follow to diagnose and potentially resolve the issue. Here’s a structured approach:

• Check the Vehicle’s Manual: Refer to the vehicle’s service manual for specific information regarding the air temperature sensor and the related circuit.
• Visual Inspection: **Wiring and Connectors: Inspect the wiring harness and connectors associated with the air temperature sensor for any signs of damage, corrosion, or loose connections.
• **Sensor Condition: Check the air temperature sensor itself for physical damage or contamination.
• Test the Sensor: **Resistance Check: Use a multimeter to measure the resistance of the air temperature sensor. Compare the readings to the specifications provided in the service manual. A significant deviation may indicate a faulty sensor.
• **Voltage Check: With the ignition on (engine off), check the voltage at the sensor connector. Ensure it is within the expected range as per the specifications.
• Inspect the Circuit: **Continuity Test: Perform a continuity test on the wiring between the sensor and the Engine Control Module (ECM) to ensure there are no breaks in the circuit.
• **Ground Check: Verify that the ground connection for the sensor is intact and functioning properly.
• Check for Short Circuits: Inspect the wiring for any signs of short circuits to ground or to other wires that could cause an open circuit condition.
• Scan for Additional Codes: Use an OBD-II scanner to check for any other related trouble codes that may provide additional context or indicate a broader issue.
• Clear Codes and Test Drive: After performing the checks and repairs, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code reappears.
• Replace the Sensor (if necessary): If the sensor is found to be faulty after testing, replace it with a new one and recheck the system.
• Consult a Professional: If the issue persists after following these steps, it may be beneficial to consult a professional mechanic or technician who has experience with your specific vehicle make and model.Additional Tips: – Always ensure that you are working safely and disconnect the battery when working on electrical components. – Keep in mind that intermittent issues can sometimes be harder to diagnose, so thorough testing is essential. By following these steps, you should be able to identify and resolve the issue related to the B1251 code.