B1255 — Air Temperature External Sensor Circuit Open #

Note: The description for DTC B1255 may vary depending on the vehicle manufacturer.

Known Variations in Code Description:

• Ford: Outside Air Temperature Sensor Circuit Open
• Toyota: Ambient Air Temperature Sensor Circuit Open
• GM/Chevrolet: Outside Air Temperature Sensor Circuit Malfunction
• Honda: Outside Temperature Sensor Circuit Open

Summary of DTC B1255 #

Diagnostic Trouble Code B1255 points to an open circuit in the external air temperature sensor system. This sensor, also known as the ambient air temperature sensor, provides real-time outside temperature information to the vehicle’s control modules, such as the climate control unit or body control module. When the circuit is “open,” it means the signal from the sensor is interrupted—either due to a wiring issue, a faulty sensor, or a connector problem. As a result, the system cannot read accurate outside air temperature data, potentially affecting automatic climate control performance and external temperature displays. While this issue doesn’t usually impact the engine’s operation, it can influence comfort and some automatic functions.

Common Symptoms for Code B1255 #

When B1255 is stored, you’ll usually notice changes in how your vehicle displays or uses outside temperature data. Symptoms may vary depending on the make and model, but include:

• Incorrect outside temperature displayed (often a default value like -40°F or 140°F)
• Automatic climate control not functioning properly or using default settings
• Warning lights or messages related to the climate system
• Loss of auto HVAC features (like automatic blower or recirculation control)
• No change in outside temp reading regardless of actual weather

Most Likely Causes for DTC B1255 #

The B1255 code is most often caused by issues interrupting the signal from the external (ambient) air temperature sensor to the control module. Here are the most common culprits, ranked by frequency:

1. Faulty ambient air temperature sensor
2. Open circuit or broken wire in the sensor harness
3. Corroded or disconnected sensor connector
4. Water intrusion or damage at connector
5. Faulty wiring between sensor and control module
6. Rarely: Control module (e.g., HVAC control unit) fault

Step-by-Step Diagnosis for B1255 #

A careful diagnosis will help you avoid unnecessary parts replacement and quickly restore correct operation. Here’s a proven process:

• 1. Confirm the code using a compatible scan tool. Clear the code and see if it returns.
• 2. Visually inspect the ambient air temperature sensor (usually located in the front grille or bumper). Check for obvious damage or disconnection.
• 3. Inspect the connector for corrosion, bent pins, or water intrusion.
• 4. Check the sensor wiring harness for breaks, pinches, or chafing, especially near the front of the vehicle.
• 5. Test the sensor with a multimeter. Most use a thermistor (variable resistor): compare resistance values to OEM specifications at ambient temperature.
• 6. Check for voltage or ground at the connector per OEM wiring diagram.
• 7. If wiring and sensor test OK, suspect a fault in the control module or wiring between the sensor and the module.

Possible Repairs for B1255 #

The right repair will depend on your diagnostic findings. Targeted fixes include:

• Replace the ambient (external) air temperature sensor if it fails resistance or continuity checks
• Repair or replace damaged wiring between the sensor and the control module
• Clean or replace corroded connectors, ensuring a snug fit and weatherproofing
• Secure any loose sensor connectors
• Address water intrusion issues with new seals or relocation (if recommended by OEM)
• Rarely: Replace the HVAC or body control module if all other checks are conclusive

Is It Safe to Drive With B1255? #

Yes, you can continue to drive your vehicle with code B1255 present. This code only impacts the outside air temperature reading and the automatic climate control’s ability to adjust settings based on outside air temperature. Engine performance, safety, and drivability are not affected. However, you may notice discomfort due to inaccurate climate control, and you’ll lose some convenience features like automatic cabin temperature regulation.

Vehicles Most Commonly Affected by B1255 #

While almost any modern vehicle with automatic climate control or a digital outside temperature display can set code B1255, it’s especially common on:

• Ford (F-150, Explorer, Fusion, Escape, Edge)
• Toyota (Camry, Corolla, Highlander, RAV4)
• GM (Chevrolet Silverado, GMC Sierra, Buick Enclave)
• Honda (Accord, CR-V, Pilot)
• Hyundai/Kia (Sonata, Santa Fe, Sorento)

Common Mistakes & Best Practices for B1255 #

To save time and money, avoid these frequent pitfalls, and follow these best practices:

• Replacing the sensor without checking wiring — always inspect wiring and connectors first.
• Ignoring corrosion or water intrusion — this often causes intermittent faults.
• Assuming all sensors are the same — use only OEM or OEM-equivalent parts for compatibility.
• Skipping a scan tool check after repair — always clear the code and confirm the fix.
• Not checking related TSBs (Technical Service Bulletins) — some OEMs have updates for this exact issue.

Quick FAQ for B1255 #

Q: Will B1255 cause my check engine light to come on?
A: Typically, B1255 triggers a warning related to the climate system, not the main engine warning light (MIL). However, some vehicles may display a general warning message.

Q: Can I replace the sensor myself?
A: Yes, on most vehicles, the ambient air temperature sensor is accessible in the front grille or bumper area. Basic tools and care with connectors are usually all that’s needed, but always disconnect the battery before working on electrical components.

Q: Will this affect my A/C or heating?
A: It may affect automatic functions, but manual operation is usually still available. Your system may default to “basic” mode until the fault is fixed.