P0168 Fuel temperature too high

P0168 Fuel temperature too high

OBD-II DTC Datasheet

Fuel temperature too high

What does this mean?

This Diagnostic Trouble Code (DTC) is a generic transmission code, which means it applies to OBD-II equipped vehicles (Dodge, Ram, Ford, GMC, Chevrolet, VW, Toyota, etc.). Although general in nature, the specific repair steps may differ depending on the brand / model.

I found that when the OBD II vehicle stored the P0168 code, it means that the powertrain control module (PCM) has detected a voltage signal from the fuel temperature sensor / fuel composition sensor or circuit that indicates too high fuel temperature.

The fuel temperature sensor is usually built into the fuel composition sensor. It is a small computerized device (similar to a fuel filter) designed to provide the PCM with accurate analysis of fuel composition and fuel temperature.

The fuel that passes through the built-in sensor is electronically analyzed to determine its ethanol, water, and unknown (non-fuel) contaminants. The fuel composition sensor not only analyzes the fuel composition, but also measures the fuel temperature and provides an electrical signal to the PCM that reflects not only what pollutants are present (and the degree of fuel contamination), but also the fuel temperature. The degree of fuel contamination is analyzed by the percentage of pollutants in the fuel; formation of a voltage signature in the fuel composition / temperature sensor.

The voltage signature is entered into the PCM as square-wave voltage signals. The waveform patterns differ in frequency depending on the degree of fuel contamination. The closer the waveform frequency, the higher the degree of fuel contamination; this constitutes the vertical portion of the signal. The fuel composition sensor analyzes the amount of ethanol present in the fuel separately from other contaminants. The pulse width or horizontal portion of the waveform indicates the voltage signature generated by the temperature of the fuel. The higher the temperature of the fuel passing through the fuel temperature sensor; the faster the pulse width. Typical pulse width modulation ranges from one to five milliseconds, or hundredths of a second.

If the PCM detects an input from the fuel temperature / composition sensor that indicates that the fuel temperature is too high, a P0168 code will be stored and a malfunction indicator lamp (MIL) may illuminate. On some models, several ignition cycles (with a malfunction) may be required to turn on the warning lamp of the warning lamp.

Code severity and symptoms

A stored P0168 code should be considered severe because the fuel temperature is used by the PCM to calculate the fuel delivery strategy in flex-fuel vehicles.

Symptoms of this code may include:

• Typically, the P0168 code is asymptomatic.
• Other fuel composition codes may be present.
• The MIL will eventually light up.

reasons

Possible reasons for setting this code:

• Defective fuel composition / temperature sensor
• Bad ambient temperature sensor
• Intake air temperature sensor defective
• Open, short, or damaged wiring or connectors
• PCM or PCM programming error

Diagnostic and repair procedures

A good starting point is always to check the Technical Service Bulletins (TSB) for your particular vehicle. Your problem may be a known issue with a known manufacturer-released fix and could save you time and money while troubleshooting.

To diagnose the P0168 code, you will need a diagnostic scanner, a digital volt / ohmmeter (DVOM), an oscilloscope, an infrared thermometer, and a vehicle information source (such as All Data DIY). In this situation, a diagnostic scanner with a built-in DVOM and a portable oscilloscope will come in handy.

To maximize your chances of a successful diagnosis, start by visually inspecting all associated wiring harnesses and connectors. If necessary, you will need to repair or replace damaged or burnt components and retest the system.

Most fuel temperature sensors are provided with a XNUMX B reference and ground. As a variable resistance sensor, the fuel temperature sensor closes the circuit and outputs the appropriate waveform to the PCM when fuel is flowing. Using the DVOM, check the reference voltage and ground at the fuel temperature sensor connector. If no voltage reference is available, use the DVOM to test the appropriate circuits at the PCM connector. If a voltage reference is found at the PCM connector, repair the open circuits as necessary. Caution: Disconnect all related controllers before testing circuit resistance with the DVOM.

Suspect a defective PCM (or programming error) if there is no voltage reference at the PCM connector. If there is no fuel temperature sensor ground, use your vehicle information source and find a suitable ground to make sure it is reliable.

Use an oscilloscope to view real-time data in graphs if a reference signal and ground are present at the fuel temperature sensor connector. Connect test leads to the appropriate circuits and observe the display screen. Measure the actual fuel temperature with an infrared thermometer and compare the results with the temperature displayed on the oscilloscope charts. If the fuel temperature displayed on the oscilloscope does not match the temperature of the infrared thermometer, suspect that the fuel temperature sensor is defective.

Additional diagnostic notes:

• Use the DVOM to test the resistance of the fuel temperature sensor according to the manufacturer's recommendations.
• If the actual fuel temperature is higher than acceptable, check for a short circuit in the wiring or improperly routed exhaust gases near the fuel tank or supply lines.

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