P0186 OBD-II Trouble Code: Fuel Temperature Sensor "B" Circuit Range/Performance

P0186 trouble code definition

Fuel Temperature Sensor "B" Circuit Range/Performance

What the P0186 code means

P0186 is a generic OBD-II code that is triggered when the fuel temperature sensor B circuit goes out of range during self testing; the sensor voltage falls below or goes above the calibrated limit specifications during the self test.

What causes the P0186 code?

• The engine control module (ECM) detects the sensor circuit voltage below or above the specified range designed for the sensor when it is tested during startup or during operation.

• Intermittent wiring or connections

• ECM or sensor short, or open faults

• Cold fuel resulting from extreme cold conditions (below -40 degF).

• A corroded or insecure connector could cause the fuel tank or fuel rail temperature sensor to go out of sensor range .

• Shorted wiring to the sensor, or internal shorting of a defective ECM

What are the symptoms of the P0186 code?

• The ECM sets code P0186 to memory and turns on the Check Engine Light.

• The vehicle will not start if the fuel is frozen from extreme cold or there is water in the fuel.

• The vehicle will not start or may lose power and stall if the fuel gets too hot and boils off.

• Excessive additives in the fuel can cause erratic sensor readings and cause the fuel to boil off at lower temperatures causing sensors to malfunction.

How does a mechanic diagnose the P0186 code?

• Scans codes and documents the freeze frame data, then clears the codes to verify code returns

• Performs a visual check of all the wiring and connections to the sensor to check for breaks in the wiring or loose connections

• Disconnects connection to the sensor and checks to see if the sensor is testing within specifications

• Takes a fuel sample to compare the temperature of the fuel to the sensor input

• Tests the diesel fuel heater for proper operation to make sure that it is not overheating the fuel

Common mistakes when diagnosing the P0186 code

• Not doing a visual check of connections to the sensor to make sure they are making good contact to the fuel heater and fuel temperature sensor

• Not checking the fuel for excessive additives that can cause sensors to malfunction

• Not retesting the system in a warmer area if the car is in an extremely cold environment (below -40 degrees Fahrenheit) which can cause codes without failure

How serious is the P0186 code?

• The vehicle will not start if excessive water is in the fuel, the ambient temperature is below freezing, or the fuel heater is defective due to the temperature sensor

• The engine may misfire, hesitate and stall if the fuel temperature exceeds normal operating temperatures due to the temperature sensor circuit malfunction, or if the fuel rail gets too hot

What repairs can fix the P0186 code?

• Testing the fuel temperature sensor and replacing it if it goes out of specifications
• Repairing or replacing a defective connector or wiring to the sensor if it is shorted or open
• Replacing a defective ECM
• Replacing the diesel fuel heater and the temperature sensor as an assembly

Additional comments for consideration regarding the P0186 code

The code P0186 may be used on diesel engines with fuel heaters, and on gasoline engines that use two fuel temperature sensors to monitor the fuel temperature in the fuel tank or at the fuel rail. Follow the manufacturer's recommended testing procedures for the vehicle and type of fuel you are working on. Not all temperature sensors are located and tested the same.

Need help with a P0186 code?

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