B1251MinorHVAC

B1251: Air Temperature Internal Sensor Circuit Open

3 vehicles · 1 makes · $25-$700 repair

Most Reported On

2009-2019Ford Flex 2011-2019Ford Explorer 2007-2020Ford EdgeSE +5

B1251 is an OBD-II diagnostic trouble code meaning “Air Temperature Internal Sensor Circuit Open.” A Ford-specific code set by the HVAC control module (EATC/DATC) for the in-vehicle, or internal, air temperature sensor. The module sees no voltage drop on the sensor's reference voltage circuit, which indicates an open circuit. Ford's pinpoint test for it lives in the heating and air conditioning section and is shared with B1253 (short to ground). Automatic climate control loses its cabin temperature input, so it may blow full hot or full cold and ignore the set temperature. It is a comfort fault, not a safety one. This code is most commonly reported on 2009-2019 Ford Flex, 2011-2019 Ford Explorer, and 2007-2020 Ford Edge (SE, SEL, Limited, Titanium, Sport, ST), with repair costs ranging from $25 to $700.

Common Causes

1Failed in-vehicle air temperature sensor

2Open or broken wire in the sensor signal or ground circuit

3Disconnected or corroded sensor connector

4Blocked or disconnected aspirator hose/tube on sensors that use one

5Faulty EATC/HVAC control module

6Damaged wiring from prior dash, HVAC, or radio work

Typical Repair Cost

$25 - $700

Based on 3 documented vehicle-specific issues. Actual cost depends on root cause and vehicle.

Diagnostic Tools

B1251 does not use the standard P/B/C/U prefix. It may be a manufacturer-specific code, so verify that a scanner supports your exact year, model and module before buying.

Vehicles Affected (3)

Ford B1251 page →

FlexMinor

HVAC Blend Door Actuator Gear Stripping Causes Clicking and Split Cabin Temperatures

2009-2019$120-$700

ExplorerMinor

HVAC Blend Door Actuator Failure Causing Clicking Noise and No Heat or A/C

2011-2019$25-$350

EdgeModerate

HVAC Temperature Blend Door Actuator Failure - Heat or A/C on One Side Only

2007-2020$180-$650

FAQ

What does B1251 mean?

B1251 stands for "Air Temperature Internal Sensor Circuit Open." A Ford-specific code set by the HVAC control module (EATC/DATC) for the in-vehicle, or internal, air temperature sensor. The module sees no voltage drop on the sensor's reference voltage circuit, which indicates an open circuit. Ford's pinpoint test for it lives in the heating and air conditioning section and is shared with B1253 (short to ground). Automatic climate control loses its cabin temperature input, so it may blow full hot or full cold and ignore the set temperature. It is a comfort fault, not a safety one.

What are the most common causes of B1251?

The most common causes of B1251 are: Failed in-vehicle air temperature sensor, Open or broken wire in the sensor signal or ground circuit, Disconnected or corroded sensor connector, Blocked or disconnected aspirator hose/tube on sensors that use one, Faulty EATC/HVAC control module, Damaged wiring from prior dash, HVAC, or radio work. The specific cause varies by vehicle.

How much does it cost to fix B1251?

Repair costs for B1251 range from $25 to $700, depending on the vehicle and root cause.

Which vehicles are affected by B1251?

Au7o has documented B1251 across 3 vehicle models from 1 manufacturers: Ford.

Sources (7)

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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.