What Does B1255 Mean?
This code indicates that the Body Control Module (BCM) has detected an open circuit in the external ambient air temperature sensor circuit. An open circuit means there is a break in the electrical pathway, preventing the sensor from sending temperature data to the BCM. This sensor is typically used for climate control operation, outside temperature display, and engine cooling fan logic on some vehicles.
Common Causes
35%
Broken or corroded wiring between the ambient air temperature sensor and BCM, often damaged by road debris or corrosion
30%
Failed ambient air temperature sensor with internal open circuit
25%
Disconnected or severely corroded electrical connector at the sensor
10%
Damaged BCM internal circuit or connector pin damage at BCM
Diagnostic Steps
1
Step 1: Visually inspect the ambient air temperature sensor location (typically mounted in front bumper area or near radiator) for physical damage, disconnected connectors, or obvious wiring damage from road debris
2
Step 2: Using a digital multimeter, measure the resistance of the ambient air temperature sensor (disconnect sensor connector). Typical values range from 2-10k ohms at 70°F depending on manufacturer. Compare to service specifications. Infinite resistance indicates open sensor
3
Step 3: With sensor disconnected, check for continuity in the wiring harness between the sensor connector and BCM connector using a wiring diagram. Check both signal and ground circuits. Infinite resistance indicates open circuit in wiring
4
Step 4: Inspect all connectors for bent pins, corrosion, or moisture intrusion. Clean connectors with electrical contact cleaner and ensure pins make proper contact. Check connector terminal tension
5
Step 5: If wiring and sensor test good, check voltage supply at sensor connector with ignition on (typically 5V reference). No voltage indicates BCM or power supply issue
6
Step 6: After repairs, clear codes and verify sensor reading on scan tool matches actual ambient temperature. Perform drive cycle to confirm code does not return
Estimated Repair Cost
$75 - $350
Parts + labor, varies by vehicle and location
This code indicates that the Body Control Module (BCM) has detected an open circuit in the external ambient air temperature sensor circuit. An open circuit means there is a break in the electrical pathway, preventing the sensor from sending temperature data to the BCM. This sensor is typically used ...
The most common cause of B1255 (Air Temperature External Sensor Circuit Open) is: Broken or corroded wiring between the ambient air temperature sensor and BCM, often damaged by road debris or corrosion
Typical repair costs for B1255 range from $75 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
This code does not affect vehicle safety or drivability. The vehicle is safe to continue driving, though climate control performance may be affected and outside temperature display will be inaccurate or non-functional. Repair can be scheduled at convenience.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1255 to identify the root cause.
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Quick Info
Category
Body
System
Climate Control and Information Display
Difficulty
Type
Manufacturer
Recommended Tools
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