B1250

Air Temperature Internal Sensor Circuit Failure

Body Engine Cooling Climate Control Sensor 🟢 Low — Fix at next service ✅ Safe to Drive
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What This Actually Means

In plain language — no jargon

Your vehicle's interior air temperature sensor has failed or lost connection, like a broken thermometer that can't tell the climate control system how hot or cold the cabin is. The system can't properly adjust heating or cooling without this reading.

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Symptoms You May Notice

3 known symptoms for this code
Climate control not functioning properly or blowing wrong temperature air
Check engine light or service message displayed on dashboard
Inconsistent cabin temperature despite adjustment attempts
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECU monitors the interior air temperature sensor voltage to regulate cabin climate. It expects a gradually changing voltage signal proportional to cabin temperature. If voltage is out of range, stays static, or drops to zero, the ECU detects a circuit failure.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Sensor Voltage 0.5–4.5V (varies with temperature) <0.1V or >4.9V sustained
Signal Rate of Change Gradual variation over time No change or erratic spikes
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Cabin air temperature sensor connector
Locate the sensor (usually in dashboard air duct) and reseat the connector firmly, checking for corrosion or bent pins.
2
Cabin air temperature sensor wiring
Inspect the wiring harness from sensor to ECU for cuts, pinches, or water damage; repair or replace damaged sections.
3
Cabin air temperature sensor
Replace the sensor itself if connector and wiring are intact; typically located in the HVAC plenum behind the dashboard.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code B1250 is a low-severity fault. Your vehicle is generally safe to drive to a workshop for diagnosis. However, do not ignore it indefinitely — low-severity codes often indicate developing problems that become expensive if neglected. Book a diagnostic appointment within 2–4 weeks. If you notice any additional symptoms (rough running, power loss, unusual smells), treat it as higher priority.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.
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How to Clear Code B1250

What happens after you fix the fault

Once the fault is repaired, B1250 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.

The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.

✅ Safe to Clear When
  • Fault has been diagnosed and repaired
  • You want to confirm the repair worked
  • Code appeared after a sensor was cleaned
⚠️ Do Not Clear When
  • Preparing for an emissions/PUC test
  • Root cause is still undiagnosed
  • Check engine light is flashing
Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.