Code
B1223
ALFA ROMEO
B — Body
Fuel temperature sensor 1 open circuit
Views:
UK: 7
EN: 9
RU: 9
AI status
Completed
Completed
100%
Causes
- Open or broken sensor wiring (cut/rodent damage, chafing)
- Disconnected, corroded or pushed-out connector/pins
- Failed fuel temperature sensor (internal open)
- Poor or missing ground or reference supply to the sensor
- ECU input circuit fault (rare)
Symptoms
- Malfunction Indicator Lamp (MIL) / check engine light illuminated
- Stored B1223 and possibly related fuel/temperature codes
- Erratic fuel trim or drivability issues during warm-up
- Hard start or richer/leaner than expected mixture in some conditions
- Possible reduced fuel economy or increased emissions
What to check
- Read and record freeze-frame and live data with a diagnostic scanner (fuel temp value and related parameters)
- Visually inspect sensor connector and harness for damage, corrosion, water ingress or pulled pins
- Wiggle harness and connector while monitoring live data or scanner for intermittent changes
- Measure continuity between sensor harness pin and ECU connector pin; check for open circuit
- Measure sensor resistance at ambient and compare to expected NTC range (see signal parameters)
- Check sensor supply/reference voltage and ground at the connector with key on
Signal parameters
- Sensor type: typically an NTC thermistor (resistance falls as temperature rises)
- Typical resistance: commonly in the low kΩ range at 20–25°C (example 1–10 kΩ; consult vehicle-specific data for exact values)
- ECU reads a voltage corresponding to the thermistor resistance (0–5 V range typical)
- An open circuit usually shows very high/infinite resistance or an out-of-range voltage (sensor reported as 'open' or extreme temperature)
- Response: resistance should change smoothly with temperature (immersion in ice water and warm water will show distinct, predictable changes)
Diagnostic algorithm
- Connect a manufacturer-level or compatible scan tool. Retrieve B1223 and any related codes; record freeze-frame data and live fuel temperature reading.
- Visually inspect sensor location, connector, and wiring for obvious damage, contamination, or poor seating. Repair or clean as needed.
- With ignition ON (engine OFF), back-probe the sensor connector. Verify reference voltage (if present) and ground continuity to chassis/ECU. Compare to vehicle manual values.
- Measure sensor resistance by disconnecting the sensor and using an ohmmeter across sensor terminals. Compare to expected range at ambient temperature. If infinite/open, sensor is faulty.
- If resistance is within range, check continuity between the sensor connector and the ECU input pin. Repair any open or high-resistance wiring/connector faults.
- Perform a wiggle test on harness while observing live data to find intermittent opens. Repair harness if the signal drops or faults reappear.
- If wiring and sensor are good but fault persists, verify ECU input with oscilloscope or specialized tool (advanced) or consult wiring diagrams; consider ECU fault only after eliminating harness/sensor.
- After repairs or sensor replacement, clear codes and perform a road/test cycle to verify code does not return and that fuel temperature reading behaves normally.
Likely causes
- Damaged or disconnected harness/connector at the fuel temperature sensor
- Failed sensor element (open thermistor)
- Corroded terminal or poor connector contact
- Intermittent wiring/connector fault revealed by vibration or heat
- Less likely: ECU input driver fault
Fault status
Status
Fuel temperature sensor 1 open circuit detected — ECU not receiving valid fuel temperature input. ECU may use default fuel mapping and set MIL.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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