P0181 OBD-II: Fuel Temperature Sensor "A" Circuit Range/Performance

What does code P0181 mean?

Code P0181 stands for Fuel Temperature Sensor 'A' Circuit Malfunction

The fuel tank temperature sensor (FTS) is used to determine fuel temperature inside the fuel tank. This information is used by the vehicle's onboard computer, the engine control module (ECM), to help determine fuel injector control.

On most vehicles, the ECM sends the FTS a reference voltage. The FTS then varies its internal resistance according to fuel temperature and the modified voltage signal is read by the ECM. The FTS is a type of sensor called a thermistor. Its internal resistance decreases as temperature increases.

The 5-volt signal from the ECM is both the reference voltage and return input. When the sensor temperature increases, its resistance is reduced. This also reduces the voltage on the reference connection to the ECM. This reduced voltage is interpreted by the ECM as a higher temperature.

Code P0181 indicates the ECM has detected a problem with the fuel temperature sensor 'A'. The 'A' part of the code indicates the problem is with sensor one of two, should the vehicle have more than one fuel temperature sensor.

P0181 symptoms

• An illuminated check engine light
• Engine performance problems

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Common causes for P0181

Code P0181 is typically caused by one of the following:

• A faulty fuel tank temperature sensor
• Wiring problems
• A problem with engine control module

How to diagnose and repair P0181

Perform a preliminary inspection

Sometimes P0181 can pop up intermittently. This is especially true if the code is a history code and not current. Clear the code and see if it returns. If it does, the next step is to perform a visual inspection. A trained eye can check for issues such as broken wires and loose connections. If a problem is found, the issue should be repaired and the code cleared. If nothing is discovered, check for technical service bulletins (TSBs). TSBs are recommended diagnostic and repair procedures put out by the vehicle manufacturer. Finding a related TSB can greatly reduce diagnostic time.

Check the FTS

Typically, the next thing a technician will do is check the FTS. This can be accomplished by measuring the sensors internal resistance with a digital multimeter (DMM) and comparing it to the manufacture's specifications. The sensors resistance should decrease as temperature increases. For example, the repair information for one vehicle specifies the resistance should be between 2.3 to 2.7 ohms when the temperature is 68 degrees Fahrenheit, while it should be 0.79-0.90 ohms when the temperature is 122 degrees.

Check the circuit

If the FTS checks out OK, its circuit should be checked next. This can be done using a DMM. The FTS will have two wires going to it: signal and return (ground).

The DMM should measure approximately 5-volts coming to the sensor on the signal wire. To check the return side of the circuit, the DMM should be switched to the ohmmeter setting. Continuity should be measured between the FTS return wire and ground. If an issue is found with either portion of the circuit, the factory wiring diagram will need to be traced pinpoint the problem. Then, the problem can be repaired and the code cleared.

Check the ECM

In rare cases, the ECM may be at fault. The ECM should supply a 5-volt reference to the FTS at all times. If it does not, it may be faulty or require reprogramming.

Other diagnostic codes related to P0181

• P0180: Code P0180 indicates the engine control module (ECM) has detected a fuel temperature sensor 'A' circuit malfunction.
• P0182: Code P0182 indicates the engine control module (ECM) has detected a low input signal from fuel temperature sensor 'A'. This typically indicates a short circuit.
• P0183: Code P0183 indicates the engine control module (ECM) has detected a high input signal from fuel temperature sensor 'A'. This typically indicates an open circuit.
• P0184: Code P0184 indicates the engine control module (ECM) has detected an intermittent problem with the fuel temperature sensor 'A' circuit.
• P0185: Code P0185 indicates the engine control module (ECM) has detected a fuel temperature sensor 'B' circuit malfunction.
• P0186: Code P0186 indicates the engine control module (ECM) has detected a fuel temperature sensor 'B' circuit range/performance problem.
• P0187: Code P0187 indicates the engine control module (ECM) has detected a low input signal from fuel temperature sensor 'B'. This typically indicates a short circuit.
• P0188: Code P0188 indicates the engine control module (ECM) has detected a high input signal from fuel temperature sensor 'B'. This typically indicates an open circuit.
• P0189: Code P0189 indicates the engine control module (ECM) has detected an intermittent problem with the fuel temperature sensor 'B' circuit.

Code P0181 technical details

Depending on the manufacturer, code P0181 can stand for either Fuel Tank Temperature Sensor or just Fuel Temperature Sensor.