B1222

Code

Other B — Body

Fuel Temperature Sensor #1 Circuit Failure

Brand: Other

Type: B — Body

Views: UK: 32 EN: 60 RU: 32

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Page language: EN

Causes

Broken, bent, corroded or disconnected wiring or connector at the fuel temperature sensor
Open or shorted sensor element (thermistor)
Short to power or short to ground in the sensor circuit
Poor ground or reference voltage at the ECM connector
Corroded or water-intruded connector, dirt or fuel contamination
Faulty ECM or an intermittent ECM input driver (less common)

Symptoms

MIL (Check Engine Light) illumination
Possible rough idle or drivability issues if fuel temperature reading drives fuel trim aggressively
Hard starts or poor cold/hot performance (less common)
Stored fuel temperature value missing or stuck at an extreme value in scan tool data

What to check

Confirm DTC: retrieve stored/confirmed counts and any freeze frame data using a scan tool
Visually inspect fuel temperature sensor and harness for damage, corrosion, pin push-out, fuel intrusion or loose connector
Backprobe the sensor connector and wiggle harness while monitoring live data for intermittent changes
Check for related codes (ECU power/ground or communication faults)
Record fuel temperature reading from scan tool at different ambient/engine conditions and compare to expected behavior

Signal parameters

Sensor type: typically NTC thermistor (negative temperature coefficient)
Typical resistance behavior (approximate): ~5–20 kΩ at -20°C, ~1–5 kΩ at 20–25°C, ~200–800 Ω at 80°C (manufacturer-specific)
Typical signal voltage at ECM: roughly 0.2–4.8 V depending on temperature and circuit design (pull-up/pull-down dependent)
Reference: ECM provides a stable pull-up or pull-down/reference voltage (often 5 V or an internal reference); good ground required
Circuit failure symptoms: open circuit → voltage near reference (high or low depending on design); short to ground/power → voltage near 0 V or near reference voltage

Diagnostic algorithm

Retrieve and record freeze frame and live fuel temperature values with a scan tool; note whether value is fixed or varying
Inspect sensor and connector: unplug connector, check terminals for corrosion, bent pins, fuel contamination and secure fit
Measure sensor resistance cold (engine off) at the sensor connector and compare to expected thermistor resistance table for approximate ambient temperature (if manufacturer table not available, expect rough NTC behavior: resistance decreases as temperature rises)
Backprobe sensor signal pin with ignition ON and measure voltage at the sensor while connected; verify against expected voltage range (0.2–4.8 V typical)
Probe at the ECM connector for signal, reference and ground. Verify continuity of wiring between sensor and ECM pins and check for short to battery positive or ground (use ohmmeter with battery disconnected)
Perform wiggle test: while monitoring live data or voltage, move the harness to reproduce intermittent faults
If wiring and connector are good but readings are out of range, replace the sensor and re-test
If new sensor shows same fault and wiring is confirmed OK, suspect ECM input or internal short; consult manufacturer service information before replacing ECM
Clear codes after repairs and perform a test drive/cycle to confirm code does not return

Likely causes

Damaged/loose connector at the fuel rail sensor
Open/shorted wiring between sensor and ECM due to chafing or rodent damage
Failed fuel temperature sensor (thermistor out of range)
Connector corrosion or pin push-out causing intermittent contact

Fault status

⚠️ Status

B1222 — Fuel Temperature Sensor #1 Circuit Failure. ECM detected open, short or implausible signal from fuel temperature sensor circuit; service wiring, connector and sensor.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours