P0186: Fuel Temperature Sensor B Circuit Range/Performance

What it means

Fuel temperature sensor B reading is within electrical limits but implausible (no warmup change, disagrees with sensor A or ambient).

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

Fuel Temperature sensor B reports fuel temperature at the system’s second monitoring point, and the engine control module checks that value for plausible behaviour. This code sets when sensor B’s electrical signal is present but does not respond plausibly, such as staying fixed or disagreeing with sensor A or ambient conditions.

Common causes

Most likely first.

1. Sensor drifted
2. Sensor stuck

Symptoms

• Check engine light on
• Hard starting or rough running
• Reduced engine performance
• Fuel economy may worsen

How to diagnose it

1. Review freeze-frame data and compare live sensor B fuel temperature with sensor A and ambient temperature, where those readings are available.
2. After a cold soak, check whether sensor B begins at a plausible temperature using the manufacturer’s comparison method.
3. Monitor sensor B as the fuel system warms and look for a fixed reading or an implausible difference from sensor A.
4. Inspect sensor B’s connector and wiring for corrosion, looseness, chafing, or heat damage that could affect the reading.
5. If the circuit is sound, test fuel temperature sensor B against the manufacturer’s specification and replace it if it is stuck or drifting.

Common fixes

• Repair a loose, corroded, or damaged sensor B connector.
• Repair damaged wiring in the fuel temperature sensor B circuit.
• Replace fuel temperature sensor B if its reading remains implausible with a sound circuit.
• Clear the code and verify sensor B responds plausibly and agrees with other readings as specified.

Can I keep driving?

If the vehicle runs normally, cautious driving to arrange diagnosis is generally reasonable. If hard starting, rough running, or reduced power occurs, avoid long or demanding trips because the implausible sensor B reading may affect engine control.