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

Our certified mechanics come to you · 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. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 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$20.00
Toyota$20.00
BMW$20.00
SCHEDULE P0178 DIAGNOSTIC Get a fair and transparent estimate upfront

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
P0178
Check Engine Light

No more waiting rooms! Our mechanics will come to you to diagnose and fix the P0178 code.

SCHEDULE P0178 DIAGNOSTIC
Get a $20 credit for the follow-up repair

Recent Check Engine Light is on Inspection reviews

Excellent Rating


YourMechanic Check Engine Light is on Inspection Service

Average Rating

4.8/5

Number of Reviews

5,395

Rating Summary
4,978
202
50
30
135
4,978
202
50
30
135

Anthony

6 years of experience
18 reviews
Anthony
6 years of experience
Jeep Grand Cherokee - Check Engine Light is on - Carmichael, California
Anthony was great! We are very happy that we chose to go with this company instead of the overpriced and slow service we get from the Jeep dealership. He was on time and did the job just as expected. He identified a couple of other things that need to be done before the problems get worse. We appreciate having a technician give us direct feedback regarding our vehicle, rather than a service advisor (salesperson) that we've had to deal with in the past at the dealership. We'll be booking the addtional services very soon and will definitely request Anthony again now that he is familiar with our vehicle!

Michael

37 years of experience
113 reviews
Michael
37 years of experience
Subaru Forester - Check Engine Light is on - Santa Fe Springs, California
Michael was punctual and courteous. He knows what he’s doing and I would absolutely recommend him to anyone.

Anthony

6 years of experience
18 reviews
Anthony
6 years of experience
BMW 740Li - Check Engine Light is on - Roseville, California
Very helpful in finding out the fault codes in my bmw 740 li. It was simple fix and that the two tube hose just had to be connected and my drive train malfunction went away. This saved me from having to go the an expensive dealership. Anthony has a good attitude about his work.

Breck

19 years of experience
613 reviews
Breck
19 years of experience
Ram 1500 - Check Engine Light is on - Houston, Texas
Breck did a great job working on my truck. Showed up on time, found any issues I had on my truck and explained everything to me so that I understood what was going on. Went above and beyond, definitely will book him for future appointments.


Related questions

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...

More related articles

P2503 OBD-II Trouble Code: Charging System Voltage Low
P2503 code definition Charging System Voltage Low What the P2503 code means This diagnostic trouble code (DTC) indicates that the powertrain control...
P0927 OBD-II Trouble Code: Gear Shift Reverse Actuator Circuit High
P0927 code means the ECM detected a higher than normal voltage within the gear shift reverse actuator often due too mechanical issues.
P0400 OBD-II Trouble Code: Exhaust Gas Recirculation Flow Malfunction
P0400 code definition Exhaust Gas Recirculation Flow Malfunction What the P0400 code means P0400 is an OBD-II generic code that the engine...

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 (855) 347-2779 · hi@yourmechanic.com