How To Reset Fuel Composition Sensor?

Grab your scanner and connect it to your car. Make sure it is a bidirectional scanner or it can’t reset fuel composition. After that, you go to the menu and put your car’s information. Finally, navigate to Fuel Composition Reset and hit the reset option. The scanner will start resetting the fuel composition sensor. 

You are trying to start your car and suddenly face the code p0178 or p0176. It could be that your flex fuel car is showing the wrong alcohol percentage data. Obviously, it has got something to do with the fuel composition sensor.

But how to reset the fuel composition sensor?

Now, what are those options just mentioned? Let’s find that out. 

How To Reset Fuel Composition Sensor?

The process of resetting the fuel composition sensor is quite simple. First, you need to know what type of scanner will be the perfect to reset the fuel composition sensor in your flex fuel car. 

Normally, a bidirectional scanner will be the best for you due to its ability to reset fuel composition sensors.

The table below shows some of the best bidirectional scanners for fuel composition resetting. 

Innova 3100 RS$256
Launch X431 V Pro 4.0$900
Autel MaxiCOM MK908P$1839

Of course, this is not an exclusive list and there are other scanners you can use. Unfortunately, none of the scanners for fuel composition resetting is inexpensive. 

Now, following are the steps of resetting the fuel composition sensor using Autel MaxiCOM MK908 scanner on a flex fuel car with the code P0172.

Step 1: Grab your scanner and connect it to your car’s OBD connector port. 

Step 2: Now turn on the scanner and click on ‘Diagnostics’

Step 3: After that, go to ‘Active Test’ and then you will find ‘Special Function’.

Step 4: Now you have to find the option ‘Fuel Composition Reset’. Click on that and you will see fuel composition and trimming related information. You have to click on ‘Reset Counters’.

Step 5: Now, press the ESC button. Go to ‘Live Data’ and click on the Engine Live Data.

Step 6: Start the engine and then select ‘Engine Data 2’.

Step 7: Select the parameters you want to see such as short and long term fuel trim, fuel alcohol content and press ‘Show Selected’. It will display the information related to ethanol content, trimming data, etc.

Now, you are done with resetting your fuel composition sensor. 

But there are some precautionary measures you need to keep in mind. These are:

  • Make sure that no E85 fuel is used before performing the reset because the computer issues pulse wave commands and supplies more fuel than necessary to the system. This can disrupt the composition even more and might cause engine damage.
  • Do not add extra fuel if after a fuel sample test, you find that the fuel composition is too low. Fuel sample test is a method to check the fuel composition without using the scanner. To know how to perform the test, follow this Alcohol in Fuel Test and Reset – 2006 Flex Fuel Chevy Impala 

Should You Replace or Reset?

Now, what about the situation where the fuel composition sensor is badly damaged? Resetting won’t work in that case and you have to replace it.

But how can you find out if your flex fuel sensor needs replacement or resetting? You can look for the following symptoms:

  • Engine Misfire
  • Decreased Fuel Efficiency
  • Rough Idle

Whenever problems like that happen, your fuel composition sensor might need a replacement. But how do you replace flex fuel sensors? These are the steps followed typically in 2002-2004 Chevy Suburban, GMC Yukon, Chevy Tahoe, GMC Sierra and Chevy Silverado.


  • 10mm socket
  • ⅜ ratchet
  • Fuel line disconnecting tools

Step 1: Go under the car and find the fuel filter. It is near the transfer case and transmission.

Step 2: Next you will find a connector with three wires in pink, black and white. Check the voltages of the pink and black wire. It should be 13-14 V.

Step 3: Now check the white signal wire using the digital volt ohm meter and the value should be 50-150 Hz.

Step 4: Now, locate the flex fuel sensor on the feed line of the fuel system and disconnect the fuel line and connector. Unbolt it from the bracket.

Step 5: Remove the flex fuel sensor and then insert the new sensor.

Step 6: Connect the new sensor to the fuel line and the connector. 

Step 7: Start the engine and check if the codes are still there. 

However, the steps are not that easy. If you are not into DIY work, you should get it fixed from a servicing center. It should cost you around $500-600 for servicing. 

How Else Can You Fix This Problem?

You are here because you probably faced the fuel composition sensor-related codes like P0176, P0177, P0178, etc. All of them are related to the fuel composition sensor. 

If you want to understand how, you have to know how a fuel composition sensor works. 

Firstly, the fuel composition sensor keeps track of the ethanol ratio in the gasoline. It has an inlet and outlet which helps to keep track of this ethanol percentage.

Based on this ratio, it signals the PCM. Next, the ethanol supply and ignition timing are adjusted. Sort of like fuel trimming done by the fuel trim cell.

But if the ethanol ratio in the gasoline is dropped then the fuel composition sensor gets low voltage. As a result, code is generated. It could happen for reasons other than the fuel composition sensor. 

This discrepancy can be due to improper fuel lines and connectors. Either way, the point here is that this code can happen without anything wrong with the fuel consumption sensor. 

This table below should direct you on how to go through and solve each of the problems.

Faulty fuel capLoose fuel capReplace the Fuel cap
Clogged fuel filterDifficulty in startingEngine MisfireDecreased PowerFuel LeakRandom Misfire or Rough IdleUnclog or clean the fuel line
Corroded connectorDifficulty in startingClean the corroded connector
Damaged wiringBad odorGradual failure of electrical componentsStarting ProblemsFix/Replace the wiring

Most of the solutions to these problems are quite straightforward. You have to identify and replace a few components. In most cases, these codes have almost the same sources of problem. You have to diagnose and solve them. 

Through this article, it should be clear how you reset the fuel composition sensor. Just grab a scan tool and select the necessary options to finally click on the Reset button. 


Can Ethanol Leak Cause Fuel Composition Sensor Circuit Low Input?

Yes, but it is rare. Fuel Composition Sensor Circuit Low Input means that the sensor is not showing the correct ratio of ethanol and gas. If there is any ethanol leak, your sensor won’t show the correct data. However, the probability of that happening is very low. 

What Would Happen If I Unplugged My Fuel Composition Sensor?

An unplugged Fuel Composition Sensor means that your engine will get an incorrect air-fuel ratio. This will reduce engine efficiency through increased fuel consumption. 

What’s The Difference Between Fuel Composition Sensor and Flex Fuel Sensor?

None, there is no difference between the fuel composition and flex fuel sensor. Both are used to measure the ethanol content and the fuel temperature in the flex fuel engine. 


Hopefully, this article has answered your questions on how to reset fuel composition sensors. As you can see, it is a relatively simple process. However, keep in mind that whenever the code P1078 happens it can be due to reasons other than the fuel composition sensor. So, always remember to check through the symptoms before solving.

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William Baldwin

This Is William Baldwin, The Founder & Managing Editor of this website. Me and my team share automotive tips, tricks, and news

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Talha Atta

Talha Atta, a Mechanical Engineer and experienced technical content writer and editor at with a passion for the automotive industry.