This is where a simple alcohol test of the vehicle’s fuel supply can reveal a lot of valuable information. (Note: Do not drain the fuel filter for a fuel sample to analyze. It would be best to take a sample prior to the fuel filter if possible.) By checking the fuel sample, you can learn if there is:
• Excessive percentage of alcohol in the fuel.
• Rust/debris in the fuel.
• Excessive water in the fuel (ethanol is hydroscopic).
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This simple test can either confirm there is a problem with the fuel supply or eliminate the fuel supply as being the root cause.
Diagnostic tip: Larger percentages of ethanol greater than E10 in the vehicle’s fuel system of a non-flex fuel vehicle will cause the fuel trim values to increase (positive correction) as the ECM attempts to keep the air/fuel mixture at stoichiometric. Also, my experience is that large percentages of alcohol in late model vehicles equipped with Wide Band Oxygen sensors (these sensors can provide actual air /fuel mixtures as rich as 9.0:1 and as lean as 2.0:1) can illuminate the MIL due to a fuel control failed test (DTC) without any drivability complaints or symptoms, as with the case study vehicle; 2009 Honda CR-V.
For reference, look at the image of the alcohol percentage test. This is clearly a case of excessive ethanol in the vehicle’s fuel supply. This higher than normal ethanol percentage could have been a dispensary issue (wrong fuel in the station’s tank) or human error (didn’t read the pump) on the customer’s part. Either way, our real concern is only to locate the root cause of the customer’s complaint of MIL illumination.
Now, what two options are available to us for properly repairing this vehicle? We could drain the fuel tank and refill with properly regulated <E10 fuel and reset the fuel trims. Or we could have the customer drive the vehicle until the fuel level goes below ¼ tank, then refill the tank at another location and drive the vehicle until the MIL lamp is no longer illuminated?
These would be our two repair methods, both with the same goal of replacing the fuel in the tank. (The second option would require some patience of the customer.)
If the alcohol percentage is higher than regulated with (E10) fuel, it would not be an issue what-so-ever with a flex fuel vehicle because the engine management system is designed to operate on an alcohol percentage rate as high as 85 percent (E85). It would be more of an issue with the non-flex fuel vehicles. If we overlook a basic fuel test of the vehicle’s fuel supply and the root cause of a fuel system failed test (DTC) is a higher than normal alcohol percentage, there is the strong possibility techs would attempt to correct the lean condition through the replacement of known good components (MAF sensors, HO2sensors etc.). There is also the possibility of consuming excessive shop time.