P0181 OBD-II Trouble Code: Fuel Temperature Sensor 'A' Circuit Range/Performance

P0181 code definition

Fuel Temperature Sensor ‘A’ Circuit Range/Performance

What the P0181 code means

P0181 is a generic OBD-II code that is triggered when the fuel temperature sensor ‘A’ circuit goes out of specifications during self-testing. This indicates that the sensor voltage fell below or went above calibrated limit specifications during the self-test.

What causes the P0181 code?

• The engine control module (ECM) detects that the sensor circuit is 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 faults

• The fuel is too cold from extreme cold conditions

• A corroded connector causes the fuel tank or fuel rail temperature sensor to go out of range

• The wiring to the sensor is getting shorted or the ECM is defective

What are the symptoms of the P0181 code?

• 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

• Sensors could malfunction if excessive additives in the fuel cause erratic sensor readings and cause the fuel to boil off at lower temperatures

• The ECM sets code P0181 to memory and turns on the Check Engine Light

How does a mechanic diagnose the P0181 code?

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

• Does a visual check of all the wiring and connections to the sensor, checking 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 fuel temperature to the sensor input

• Tests the diesel fuel heater for proper operation to make sure it is working to heat the fuel, without overheating the fuel

Common mistakes when diagnosing the P0181 code

Follow these simple guidelines to prevent misdiagnosis:

• Do a visual check of connections to the sensor to make sure they are making good contact to the fuel heater and fuel temperature sensor

• Check the fuel for excessive additives that can cause sensors to malfunction

• If the vehicle is in an extreme cold environment, move to a warmer area to allow the vehicle to warm up, then retest the system

How serious is the P0181 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 temperature sensor circuit malfunction, or overheated fuel rail

What repairs can fix the P0181 code?

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

Additional comments for consideration regarding the P0181 code

The code P0181 is generated on diesel engines with fuel heaters, and on gasoline engines that 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 or tested the same.

Need help with a P0181 code?

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