Code
B1250
FIAT
B — Body
Interior air temperature sensor circuit
Views:
UK: 3
EN: 5
RU: 5
AI status
Completed
Completed
100%
Causes
- Broken, corroded or disconnected sensor connector or wiring
- Interior air temperature sensor failure (thermistor or sensor element)
- Short to battery or ground in the sensor circuit
- Water ingress or contamination at sensor or connector
- Poor ground or supply to HVAC control module
- HVAC/climate control module fault or incorrect software/calibration
Symptoms
- Incorrect cabin temperature reporting on climate display
- Automatic climate control unable to maintain set temperature
- HVAC runs continuously or not at correct blower/actuator behavior
- Intermittent or permanent B1250 fault lamp/diagnostic message
- Cold/hot air delivered that does not match selected temperature
What to check
- Read freeze-frame data and pending/confirmed faults with a diagnostic scanner
- Visually inspect sensor location, connector and wiring for damage or corrosion
- Backprobe sensor connector and check reference voltage and signal (if applicable)
- Measure sensor resistance vs. temperature (thermistor) and compare to factory spec
- Check continuity and resistance of harness between sensor and HVAC module
- Inspect module power and ground circuits
Signal parameters
- Typical cabin temperature sensors are NTC thermistors: resistance decreases as temperature rises
- Example reference: ~10 kΩ at 25 °C is common for many NTC sensors (manufacturer-specific)
- If sensor is voltage-output type, expect a low-voltage signal in a range roughly 0.5–4.5 V depending on temperature (check factory data)
- Open-circuit: very high/infinite resistance or voltage at extreme endpoint; short: near 0 Ω or engine battery voltage on the signal
Diagnostic algorithm
- Connect a scan tool, read and record all climate and ambient temperature related parameters, and confirm B1250 is current or historic.
- Visually inspect sensor, connector, and wiring for damage, corrosion, or water ingress. Repair any physical damage found.
- With ignition ON, backprobe the sensor connector. Verify reference supply and ground (if present) and observe the sensor signal on the scanner or multimeter.
- With sensor disconnected, measure sensor resistance at ambient temperature and compare to manufacturer specification (if unavailable, compare to typical NTC behavior).
- Check harness continuity between sensor pins and the HVAC control module; check for short to ground or battery.
- If wiring and connector are good but sensor values are out of spec, replace the interior air temperature sensor and retest.
- Clear codes, cycle the ignition and test drive/operate HVAC to confirm code does not return.
- If fault returns and sensor/resistor checks are within spec, diagnose HVAC control module input circuitry or consult manufacturer technical bulletins; consider module repair/replacement only after wiring and sensor are verified good.
Likely causes
- Damaged sensor harness near dash or behind glovebox where it is routed
- Corroded pins or poor mating at the sensor connector
- Open or shorted sensor element (thermistor) due to age or contamination
- Connector pushed out of position or broken retainer preventing good contact
- Failed HVAC control module input stage (less common)
Fault status
Status
Interior air temperature sensor circuit — open/short/implausible signal detected by HVAC control module; stored fault requires inspection of sensor, connector, wiring and module inputs.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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