Skip the auto shop - Our mechanics make house calls

P0178 OBD-II Trouble Code: Fuel Composition Sensor Circuit Low Input

Check Engine Light

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?

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?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

How Long Does a Throttle Return Spring Last?
Not all vehicles on the road feature an electronic throttle control (ETC), which is also called drive-by-wire. For vehicles that don't offer this system, they have a throttle cable instead that...
P2159 OBD-II Trouble Code: Vehicle Speed Sensor B Range/Performance
Diagnostic Trouble Code (DTC): P2159 P2159 code definition Vehicle Speed Sensor B Range/Performance Related Trouble Codes: P2158: Vehicle Speed Sensor B P2160: Vehicle Speed Sensor B Circuit Low P2161:...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...


Related questions

Q: Sputtering, misfiring, power loss and gain

Hey there: There are usually two different mechanical problems that cause the symptoms you're describing with your Pontiac Firebird. The first and most common is a problem with the ignition coil, (especially in mid-90's GM V-6 engines) or due to...

Q: Start up is okay. Blue smoke, rough idle, and stalling. Cannot rev motor. (2002 Nissan Elgrand)

The blue smoke is due to oil leaking into the combustion chambers. The cause can vary from fairly easy to fix worn out valve stem oil seals to more costly faults such as leaking piston rings or head gasket failures....

Q: Recently had the IMRC rotary valve assembly replaced. One day later and I'm getting P1078.

Hi there. Some additional diagnostic tests will be necessary to identify the problem. The P1078 testing diagrams show that there are possible issues with a solenoid valve, a sensor, a vacuum leak, or an electrical issue. A certified mechanic will...