Code Definition

B1257 — Air Temperature External Sensor Circuit Short To Ground

System: Body  |  Type: Manufacturer-Specific  |  Make: Generic

About B1257

B1257 is a manufacturer-specific body diagnostic trouble code. It belongs to the B-prefix family of codes, which covers body, interior, airbag, or comfort-electronics faults.

When B1257 is stored, the module has detected a short-circuit (voltage pulled to ground or to supply) in the monitored circuit; and a sensor-related fault — the reported value from the named sensor is out of spec.

Scanning & clearing: Body (B) codes are often stored in the body control module, airbag module, or climate module. A basic OBD-II tool usually will not read body codes — an enhanced or OEM-level scan tool is typically required.

B1257 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

The external air temperature sensor, also known as the ambient air temperature sensor, is a negative temperature coefficient (NTC) thermistor mounted behind the front grille, inside the front bumper cover, or under an exterior mirror, positioned to measure outside air without heat soak from the engine bay. Under normal operation the climate control module supplies a 5V reference through an internal pull up resistor, and the thermistor pulls the signal toward ground by an amount that varies with temperature, returning a voltage between roughly 0.5V and 4.5V. DTC B1257 is set when the climate co...

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