Technical Description of OBD-II Trouble Code
The input for the fuel composition sensor circuit is too high.
What does that mean?
This generic powertrain diagnostic trouble code (DTC) is applicable to all OBD-II equipped vehicles, including Ford, BMW, Chevy, Pontiac, Mazda, VW, Honda, Scion, Land Rover, etc.
There are four common trouble codes associated with fuel composition sensor circuit malfunctions. This circuit is also known as the flex fuel sensor circuit, and the OBDII codes triggered by the Engine Control Module (ECM) when this circuit malfunctions are P0176, P0177, and P0178.
The fuel composition sensor circuit monitors the ethanol content in flex fuel engines. The ethanol level can vary with each tank refill, requiring adjustments for optimal performance and fuel economy. The circuit sends a signal to the ECM based on the ethanol level, and the ECM adjusts the ignition timing and fuel injector pulse width to burn the fuel more efficiently. This results in improved performance, reduced pollution, and increased fuel economy.
Code P0179 is set when the ECM detects a high voltage situation in the fuel composition sensor circuit. In most cases, the presence of a P0178 or P0179 indicates an electrical problem.
Code Severity & Symptoms
This code has a moderate severity.
Symptoms of a P0179 engine code may include:
Causes
Potential causes for this code typically include:
Common Repairs
Diagnostic and Repair Procedures
Note: The first step in troubleshooting any malfunction is to research the Technical Service Bulletins for the specific vehicle by year, model, and power plant. This can save a lot of time by pointing you in the right direction.
Basic Steps
Advanced Steps
Note: The advanced steps are vehicle-specific and require advanced equipment for accurate performance. These procedures require a digital multimeter and specific technical references for the vehicle. Voltage requirements vary based on the year, model, and engine of the vehicle.
Circuit Checks
With the key in the off position and with the sensor and ECM connected, check for power and ground using the appropriate technical data. Ground should always read 0 volts, and power should be 5 volts or 12 volts depending on the vehicle and system configuration. The specific technical manual or online reference material for your vehicle will guide you through this process. If all readings are correct, the associated component most likely requires replacement. Frequency checks are recommended in some troubleshooting procedures to pinpoint the source of the malfunction.
If this process identifies the absence of a power source or ground, continuity testing may be required to check the integrity of the wiring. Continuity tests should always be performed with the power removed from the circuit, and the normal readings should be 0 ohms of resistance unless otherwise specified by the technical data. Resistance or no continuity indicates faulty wiring that must be repaired or replaced.
Hopefully, the information in this article has been helpful in correcting the problem with your fuel composition sensor circuit malfunction. This article is strictly informational, and the specific technical data and service bulletins for your vehicle should always take priority.
