Ethanol Content sensor reading low numbers

[HopGarage]

I have my genuine GM 13507128 flex fuel sensor set up and running on DI6, but ethanol content is only reading at 65-70% when the fuel tested right at 85%. I had the tank removed and drained as much as possible before adding e85, then put in about a half gallon and drained it through the fuel return using the pump, repeated this 3 times before filling up my tank with E85.

Is my sensor not compatible, is it faulty or is there some way to calibrate it?

[Adamw]

Is ethanol temperature reading correct?

[plox]

Was part of a discussion with the e85 supplier & a tuner, sensor was reading ~73% but testing showed 85%. On two cars with different sensors/ecu etc. Was in the mist of some supply issues over a year ago but suspicion on the e85.

Could be similar or something completely different.

[HopGarage]

18 hours ago, Adamw said:

Is ethanol temperature reading correct?

I believe so. Just looked at it and with the car off in the garage and pump flowing fuel temp is between 75 and 77 degrees

[Adamw]

If the active edge was set wrong it can give incorrect ethanol %, but when set up like that the give away is temp will read very high - like 200+.   

There is nothing you can do to calibrate it - all known flex sensors output the same data/calibration.  

Provided the sensor is not a fake, my feeling is it is probably more likely the test that is inaccurate.  The "baby bottle test" used to work well about 10 years ago, but in many countries now the ethanol blends have more co-solvents or emulsifiers in them to prevent moisture from separating the components when in the storage tanks.  This means they dont separate completely with the baby bottle test either so you get a false result.  

If it was mine and I was worried, to confirm I would try mixing a small qty of my own 85% blend and pour that into the sensor to see if it reports the correct value.