P0186 moderate

Fuel Temperature Sensor B Circuit Low

The P0186 code means the vehicle's onboard diagnostic system has detected: Fuel Temperature Sensor B Circuit Low. This is a moderate severity code.

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Keep driving?: Short distances only
DIY difficulty: moderate
Estimated cost: $60 - $300 (parts and labor)

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Common Symptoms

Check Engine Light on
Fuel temperature reads extremely high on scan tool
PCM may limit engine power
Fuel system may enter protective mode

Probable Causes (Ranked by Likelihood)

Short to ground in fuel temp sensor B wiring Very High
Internally shorted fuel temperature sensor B High
Corroded connector causing low resistance Moderate
PCM input circuit fault Low

Step-by-Step Diagnostic Procedure

Read fuel temp sensor B on scan tool. A reading at maximum (e.g., 300F) with cold engine confirms low circuit.
Disconnect sensor and measure resistance. Near 0 ohms indicates internal short.
Check wiring for shorts to ground, especially near hot or vibrating components.
With sensor disconnected, verify scan tool reads minimum temperature (open circuit default).

Frequently Asked Questions

What does circuit low mean for a temperature sensor?

For NTC sensors, circuit low means low resistance, which the PCM interprets as a very high temperature. The sensor or wiring is shorted.

Can P0186 cause the engine to derate?

Yes, if the PCM believes fuel temperature is extremely high, it may reduce engine power to protect the fuel system.

How do I test the sensor?

Disconnect the sensor and measure resistance. Compare to the resistance-temperature chart in your service manual. At room temperature, expect around 2-4k ohms.