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

Our certified mechanics come to you · 12-month, 12,000-mile warranty

SCHEDULE P0178 DIAGNOSTIC Get a fair and transparent estimate upfront
Red-stars EXCELLENT RATING ON

Cost of diagnosing the P0178 code

P0178 is a diagnostic trouble code (DTC) for "Fuel Composition Sensor Circuit Low Input". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic for $70.00. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $30.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.

Cars Estimate Credit towards follow-up repair Earliest Availability
Ford$70.00$30.00
Toyota$70.00$30.00
BMW$70.00$30.00
SCHEDULE P0178 DIAGNOSTIC Get a fair and transparent estimate upfront

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.

trouble codes
Check Engine Light
P0178

Fast and easy Check Engine Light is on Inspection service at your home or office.

SCHEDULE P0178 DIAGNOSTIC
Get a fair and transparent estimate upfront

Recent Check Engine Light is on Inspection reviews

Excellent Rating


YourMechanic Check Engine Light is on Inspection Service

Average Rating

4.5/5

Number of Reviews

4,026

Rating Summary
3,683
169
45
25
104
3,683
169
45
25
104
Brandon

Brandon

15 years of experience
241 reviews
Brandon
15 years of experience
as usual, arrived on time and finished the work. Highly recommend Brandon.
2005 LEXUS RX330 - CHECK ENGINE LIGHT IS ON - DULUTH, GEORGIA
Gregory

Gregory

28 years of experience
141 reviews
Gregory
28 years of experience
Greg was on time, very personable and got right to work. Would use him again. appreciated the fact he took the time to familiarize himself with the engine light codes for my 1993 Ford before he came to the appointment.
1993 FORD E-350 ECONOLINE CLUB WAGON - CHECK ENGINE LIGHT IS ON - DENVER, COLORADO
Carlos

Carlos

14 years of experience
169 reviews
Carlos
14 years of experience
Carlos was super friendly and knowledgeable. He did a great job!
2005 FORD FOCUS - CHECK ENGINE LIGHT IS ON - NORTH HOLLYWOOD, CALIFORNIA
Peter

Peter

40 years of experience
1059 reviews
Peter
40 years of experience
Was very patient in explaining what was wrong with my vehicle. Very knowledgeable. Another great experience.
1997 JEEP GRAND CHEROKEE - CHECK ENGINE LIGHT IS ON - CHANDLER, ARIZONA

More related articles

Veteran and Military Driver Laws and Benefits in Idaho
The state of Idaho offers a number of benefits and perks for those Americans who have either served in an Armed Forces branch in the...
Veteran and Military Driver Laws and Benefits in New Mexico
The state of New Mexico offers a number of benefits and perks for those Americans who have either served in an Armed Forces branch...
Auto Safety Tips
Driving is more than a way to get from point A to point B. Owning and driving a car can also be a highly enjoyable experience. Whether a person is driving...

Related questions

Q: Check Engine Light came on. Car also has problems cranking but only when I refill it with gas.

Hi there - the first thing to do is extract the problem code(s) which are setting the "Check Engine" light. This will more efficiently direct resolution of the problem. Evaporative emission system problems are often associated with "fill-up" issues like...

Q: What Is the Problem When the Check Engine Light Comes On?

The Check Engine Light is on most vehicles built in the last twenty years. The light is used to alert the operator of the vehicle that there is a problem that needs to be looked at as soon as possible....

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...

How can we help?

Our service team is available 7 days a week, Monday - Friday from 6 AM to 5 PM PST, Saturday - Sunday 7 AM - 4 PM PST.

1-800-701-6230 · hi@yourmechanic.com