P0178 - FUEL COMPOSITION SENSOR CIRCUIT LOW INPUT

The Fuel Composition Sensor (FCS) circuit monitors the number of ethanol in the gasoline in a flex-fuel engine. The ethanol may fill the fuel tank at some point, requiring proper adjustment for optimum performance and fuel economy. This Fuel Composition Sensor circuit sends a signal to the ECM (Engine Control Module) based on the ethanol level. The ECM then adjusts the ignition timing and fuel injector pulse width, resulting in a more efficient fuel burn.

P0178 OBD2 diagnostic code is configured when the ECM determines a low voltage within the Fuel Composition Sensor circuit, it is normal when this DTC is present that the source of the problem is electrical.

• Check Engine light comes on.
• There is increased fuel consumption.
• Low performance.

When the P0178 OBDII code is set, it means that one or more of the following problems have occurred:

• The fuel cap may be defective.
• The fuel may be contaminated.
• A fuel line may be restricted or defective.
• Sensor wires or connectors are corroded or defective.
• Faulty Fuel Composition Sensor (FCS).

You can do the following to troubleshoot a P0178 fault code:

• Check the condition of the fuel cap.
• You could make sure of the fuel condition as it could be contaminated.
• Visually inspect the connection. With the circuit cable
• Visually examine the condition of the fuel line for notorious defects.
• Make sure that the electrical connections are in good working order in the face of corruption and show no wear.
• With the key in the off position and having the sensor and the Engine Control Module (ECM) connected, check the power and ground. Compare with reference specifications. Note that the ground should be 0 volts and the power should be between 5 to 12 volts which varies depending on the system configuration. If these readings are within the specifications mentioned above, the solution likely is to replace the associated component.
• If at the end of this process it is observed that the power supply or ground is deficient, you should perform continuity tests and, in this way, ensure the good condition of the wiring. This continuity test should always be done with the power removed from the circuit. The result of these readings should generally be at 0 ohms resistance in case the technical specifications indicate otherwise. When there is no continuity or resistance is not present it indicates that one of the wires is defective and should be repaired or replaced as necessary.
• You can replace the Fuel Composition Sensor (FCS).