B1255 — Air Temperature External Sensor Circuit Open

What are the symptoms of B1255?

Drivers most often notice: no impact on engine operation in most cases, the affected function (locks, windows, lighting, wipers) works intermittently or not at all, warning light on the dashboard.

What is the most common cause of B1255?

The most common causes are: corroded or loose connectors, blown fuse or failed relay, body control module (BCM) fault.

Will B1255 clear itself?

Sometimes B1255 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

Is it safe to drive with B1255?

Usually safe to drive — body codes rarely affect drivability. Exceptions: exterior lighting and wipers in bad weather, and central locking faults that can leave the car unsecured.

How do I diagnose B1255 myself?

Start with a scan: confirm B1255, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the air temperature external sensor, and verify the suspect component against live data before buying parts.

When your scan tool displays code B1255, it's telling you that the vehicle's control module has identified an open circuit condition in the outside air temperature sensor system. This falls under the body electrical category of OBD2 codes, which covers comfort and convenience systems rather than engine management.

The term "circuit open" means the electrical pathway the module expects to find is broken somewhere along its path. Instead of current flowing normally through the sensor circuit, there's a gap — a disconnection that prevents the module from reading any signal at all. This typically happens when a wire is severed, a connector is unplugged or severely corroded, a fuse has blown, or the sensor itself has an internal failure.

Your vehicle's external air temperature sensor works as a thermistor — a component that changes electrical resistance based on ambient temperature. The control module sends a small reference voltage through this circuit and interprets the returning signal to determine how hot or cold it is outside. When the circuit opens, the module receives no signal whatsoever, just like an interrupted conversation. The module logs B1255 only after confirming this open condition meets its specific fault criteria, which is why the accompanying freeze frame data is so useful — it captures the exact engine load, RPM, temperature, and vehicle speed present when the problem first appeared.

Common symptoms of B1255

• The check engine light or body system warning illuminates on the dashboard
• Climate control may revert to manual mode or default settings
• Automatic HVAC operation becomes unreliable or disabled
• The outside temperature display reads incorrect values or blanks out
• In some vehicles, related comfort functions operate intermittently
• No drivability symptoms in most cases — engine and transmission are unaffected
• The fault may be present only under certain conditions like high humidity or after vehicle sitting

What causes B1255?

The open circuit in the air temperature external sensor circuit can stem from several sources:

• A disconnected or corroded connector at the sensor or module end
• Physical damage to the wiring harness from age, chafing, or rodent intrusion
• An internally failed outside air temperature sensor (most common in older vehicles)
• Broken wires at flex points, particularly in door jambs and hatch openings
• A blown fuse protecting the body control module or related circuit
• Corrosion buildup inside connectors from moisture intrusion
• A faulty relay or poor ground connection affecting the circuit
• Body control module itself may have an internal failure (less common)

How to diagnose B1255

Follow these practical steps to isolate the root cause of the open circuit:

1. Connect your OBD2 scanner and confirm B1255 is stored, then record the freeze frame data — this information shows you precisely what conditions existed when the module first detected the fault.
2. Check for any additional trouble codes, particularly other B-series codes in the same family, as these often point to the underlying problem or related system issues.
3. Visually inspect the entire wiring harness related to the body electrical system, paying special attention to areas near the front bumper, engine bay, and interior fender wells where wires are exposed to heat and debris.
4. Perform a continuity test on the air temperature sensor circuit from the module connector to the sensor connector, and gently wiggle the harness during testing — an intermittent open will show as fluctuating resistance readings.
5. Examine all connectors for bent pins, pushed-out terminals, and greenish or white corrosion buildup; spray electrical cleaner on affected connectors and ensure a firm, seated connection.
6. Test the sensor itself with a multimeter at various temperatures to verify it responds correctly, or compare readings with a known-good sensor from the same application.
7. Clear the code, complete a full drive cycle that recreates the conditions from your freeze frame data, and verify the code does not return.

Repair options for B1255

Tackle the cheapest and most likely causes before spending money on major components:

• Wiring harness repair or connector replacement — $80–$250
• Outside air temperature sensor replacement — $120–$450
• Body control module diagnosis, repair, or replacement — $300–$900

How much does it cost to fix B1255?

Actual repair costs vary based on which component in the circuit is faulty. Using standard independent shop labor rates and typical parts pricing, here are the common scenarios for B1255 (parts and labor combined, USD):

• Wiring repair or connector replacement: $80–$250
• Outside air temperature sensor replacement: $120–$450
• Body control module service or replacement: $300–$900

Across all repair scenarios, fixing B1255 typically ranges from $80 on the low end to $900 at the extreme high end. Getting a proper diagnosis before purchasing parts is the best way to keep costs reasonable — the most expensive repair scenario is almost never where you should start troubleshooting.

Can you drive with B1255?

B1255 carries a short-term driving safety rating, meaning you can continue driving for a limited period without immediate safety concerns. Body electrical codes like this one typically do not affect engine performance, transmission operation, or braking systems. However, certain scenarios deserve attention: if the malfunction involves exterior lighting, your visibility could be compromised at night or in poor weather; wipers may stop working when you need them most; and central locking issues could leave your vehicle unsecured. Address the underlying problem within a reasonable timeframe to restore full functionality.

Related OBD2 codes

• B1200: Climate Control Pushbutton Circuit Failure
• B1201: Fuel Sender Circuit Failure
• B1202: Fuel Sender Circuit Open
• B1203: Fuel Sender Circuit Short To Battery
• B1204: Fuel Sender Circuit Short To Ground
• B1205: EIC Switch-1 Assembly Circuit Failure