P0178 code definition
Fuel Composition Sensor Circuit Low Input
What the P0178 code means
P0178 is a generic OBD-II code indicating that the diesel fuel sensor is giving a low input, which could be from an open circuit in the sensor or wiring
What causes the P0178 code?
The engine control module (ECM) detects that the sensor circuit is open if the sensor input is below specifications
The ECM detects that the circuit is open if the wiring or connection to the sensor is not making a complete circuit, such as a connection that came loose, or wiring that got cut
What are the symptoms of the P0178 code?
- The ECM sets code P0178 to memory and triggers the Check Engine Light
- The Water in Fuel Light illuminates on the instrument cluster
How does a mechanic diagnose the P0178 code?
Scans the codes and documents the freeze frame data, then clears the codes to verify code returns
Does a visual check of all the wiring and connections to the sensor, checking for breaks in the wiring or loose connections
Disconnects connection to sensor and checks to see if the sensor is testing within specifications
Common mistakes when diagnosing the P0178 code
Follow these simple guidelines to prevent misdiagnosis:
- Do a visual check of connections to the sensor to make sure they are making good contact. The connection may be loose from someone not securing it properly after servicing the filter.
How serious is the P0178 code?
Engine starting and running issues could occur if excessive water is in the fuel and the sensor cannot detect it
The engine may misfire, hesitate and stall
If there is no problems with the fuel then the only issue will be the check engine and water in fuel light will be on.
What repairs can fix the P0178 code?
- Draining off water in fuel filter and clearing Check Engine Light codes
- Replacing the open defective sensor
- Repairing the open circuit or burned wiring or connection to the sensor
- Replacing the fuel filter housing with the sensor and clearing the codes
Additional comments for consideration regarding the P0178 code
Not many manufactures use the code P0178. It is set in the computer memory to indicate that the engine fuel has, or had water in it. The code is only an indicator of water in the fuel and may be damaged by fuel additives added to the fuel.
Need help with a P0178 code?
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