Code
B1229
ALFA ROMEO
B — Body
Fuel temperature sensor 2 circuit low input
Views:
UK: 2
EN: 5
RU: 6
AI status
Completed
Completed
100%
Causes
- Short to ground in the sensor signal wire
- Open or corroded connector causing low or no signal
- Failed fuel temperature sensor (internal short or out-of-spec resistance)
- Damaged or chafed wiring harness
- ECU input or ground fault
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Stored B1229 trouble code (fuel temperature sensor 2 circuit low)
- Incorrect fuel metering or fuel trim anomalies
- Hard cold start or rough idle after cold start (if ECU relies on fuel temperature)
- Possible limp-home mode or reduced drivability depending on ECU strategy
What to check
- Read and record freeze frame and live data for fuel temperature sensor 2
- Visual inspection of sensor, connector and wiring for damage, corrosion, bent pins or water ingress
- Check for DTC presence in other related circuits (grounds, reference voltages)
- Measure voltage at the sensor signal pin with key ON (compare to reference and ground)
- Measure continuity between signal wire and chassis ground (check for unintended short)
- Measure sensor resistance at ambient and compare to expected resistance/temperature curve if available
Signal parameters
- Typical sensor signal: 0–5 V (vehicle may use 5 V or 3.3 V reference depending on model)
- Low input fault usually flagged when signal is below a low-threshold (commonly
- Sensor is usually an NTC thermistor — resistance decreases or increases with temperature depending on design
- Expected signal at ambient: moderate voltage (manufacturer-specific), not near 0 V
Diagnostic algorithm
- Connect a diagnostic scanner and confirm the B1229 code and any associated codes or freeze-frame data.
- Visually inspect Fuel Temperature Sensor 2, its connector and the wiring harness for damage, corrosion, pin push-out, or water ingress. Repair as needed.
- With the key OFF, disconnect the sensor connector and inspect terminals for corrosion, bent pins or contamination. Clean or repair connector as required.
- With connector disconnected, measure continuity between the sensor signal wire and chassis ground. If near zero ohms, repair short to ground in the harness.
- With connector disconnected, measure resistance of the sensor across its terminals. Compare to manufacturer resistance vs temperature chart if available. Replace sensor if resistance is out of range or shorted.
- Reconnect connector. With key ON (engine OFF), back-probe the signal wire and measure voltage relative to ground. Verify reference voltage to sensor (if applicable) and ECU ground integrity.
- If wiring and sensor check good but signal remains low at ECU input, inspect ECU ground and power rails. Wiggle test wiring while watching live data to reproduce fault.
- If wiring and grounds are OK and sensor replacement does not clear the fault, consider ECU input circuit fault and consult manufacturer guidance for ECU testing or replacement.
- After repairs, clear codes and perform road/test-cycle or use live data to confirm the sensor signal is stable and the B1229 does not return.
Likely causes
- Damaged sensor harness rubbed through and shorted to chassis ground
- Sensor connector corroded or pins pushed back
- Sensor element failed and is presenting near-zero resistance
- Poor ECU ground or damaged ECU input circuit
Fault status
Status
Fuel temperature sensor 2 circuit low input — ECU detects signal voltage below expected range. Likely causes include sensor failure, short to ground in the wiring, poor connector contact, or ECU input/ground fault.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
Similar codes
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email