Technical Description of OBD-II Trouble Code
Malfunction in Circuit A of the Fuel Temperature Sensor
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to OBD-II equipped vehicles (Nissan, Ford, Fiat, Chevrolet, Mercedes, Dodge, etc.). While it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
If your OBD II equipped vehicle has stored a code P0180, it means that the powertrain control module (PCM) has detected a voltage signal from the fuel temperature sensor/flex fuel sensor or circuit “A” that is outside the programmed range. “A” refers to an area of circuitry rather than a specific circuit or component.
The fuel temperature sensor is usually integrated into a single housing (along with the flex fuel sensor) known as a fuel composition sensor. It is a small computerized device designed to provide the PCM with an accurate reading of fuel composition and fuel temperature.
The fuel composition sensor calculates the fuel composition and fuel temperature by monitoring the fuel that passes through the inline sensor. It determines the presence of ethanol, water, and other contaminants in the fuel. The sensor sends an electrical signal to the PCM that reflects the contaminants present and the degree of fuel contamination. The PCM receives this signal as a square waveform of voltage, with the waveform pattern varying in frequency based on the degree of contaminants in the fuel. The fuel composition sensor also separately monitors the amount of ethanol in the fuel. Flex fuel vehicles can efficiently function with fuel composition levels as high as eighty-five-percent ethanol.
The pulse width modulation of the waveform indicates the fuel temperature. A greater pulse width speed corresponds to a higher temperature of the fuel passing through the fuel composition sensor. The pulse width modulation typically varies between one and five milliseconds.
If the PCM detects an input signal from the fuel composition sensor that indicates the fuel temperature is outside the programmed range, or if the fuel temperature varies significantly from the ambient temperature, a P0180 code will be stored and the malfunction indicator lamp (MIL) may illuminate. In some cases, multiple ignition cycles with a failure may be required for MIL illumination.
Photo of different fuel temperature sensors:
Code Severity & Symptoms
Fuel temperature is monitored by the PCM to calculate fuel delivery strategy in flex fuel vehicles, so a code P0180 should be considered severe.
Symptoms of this code may include:
Causes
Potential causes for this code to be set are:
Diagnostic and Repair Procedures
A good starting point is always to check for technical service bulletins (TSB) for your particular vehicle. Your issue may be a known issue with a known fix provided by the manufacturer, which can save you time and money during diagnosis.
To diagnose a code P0180, I would typically use a diagnostic scanner, a digital volt/ohmmeter (DVOM), an oscilloscope, an infrared thermometer, and a vehicle information source like All Data DIY. Some scanners have a built-in DVOM and portable oscilloscope, which would be useful in this scenario.
I like to begin any diagnosis with a visual inspection of all related wiring harnesses and connectors. Repair or replace any damaged or burnt components as necessary and retest the system. When multiple failure cycles are required for MIL illumination, using OBD II readiness mode can be helpful. After completing repairs, I clear the codes and operate the vehicle normally. If the PCM enters readiness mode, I know that my repairs were successful. If the code is reset, I know that a malfunction still exists.
The fuel temperature sensor (integrated into the fuel composition sensor) is typically supplied with a five-volt reference voltage and a ground. The variable resistance sensor completes the circuit. Use the DVOM to test the reference voltage and ground at the fuel temp sensor connector. If there is no reference voltage, use the DVOM to test the corresponding circuits at the PCM connector. Repair any open circuits as necessary if there is a reference voltage signal at the PCM connector. Caution: See note at the bottom of the page regarding disconnecting the controllers. If there is no fuel temp sensor ground, use your vehicle information source to locate the appropriate ground and ensure that it is secure.
If the reference and ground are present at the fuel temperature sensor A connector, connect the test leads of the oscilloscope to the appropriate circuits and observe live data in the form of waveform patterns. Use the infrared thermometer to measure the actual fuel temperature and compare it with the temperature reflected by the waveform patterns on the oscilloscope. If the fuel temperature reflected by the fuel temperature sensor does not match that of the thermometer, suspect that the fuel temperature sensor is defective.
Additional diagnostic notes:
