What sensor reads alcohol content?

sdeeter19555 · August 9, 2016

On a flex-fuel vehicle, what sensor reads alcohol content. If this sensor starts acting sluggish or reading low, would this cause any issues?

I have the ability to read alcohol content, and it used to read / fluctuate, now it seems dead and reads zero.

Sent from my SAMSUNG-SM-G900A using Tapatalk

Colossus · August 9, 2016

The PBC Sensor!

MVP9182 · August 9, 2016

Lol colossus knows what's up

Are you talking about the ones that only run flex fuel / bi-fuel stuff? I'm guessing that it's probably something similar to an O2 sensor that's on your exhaust pipe somewhere before the cats. I would imagine if it goes bad it's similar to when an O2 sensor goes bad and everything starts running sluggish because the computer is trying to control emissions

newdude · August 10, 2016

On a flex-fuel vehicle, what sensor reads alcohol content. If this sensor starts acting sluggish or reading low, would this cause any issues?

I have the ability to read alcohol content, and it used to read / fluctuate, now it seems dead and reads zero.

Sent from my SAMSUNG-SM-G900A using Tapatalk

If we are talking your 2012 HD:

E85 Flex Fuel Description
E85 compatible vehicles no longer use an alcohol sensor to determine and adjust for the alcohol content of the fuel in the tank. Instead, the vehicle calculates the alcohol content of the fuel through measured adjustments.

The ethanol calculation occurs with the engine running after a refueling event has been detected via a measured change in the fuel level sender output. The virtual flex fuel sensor (V-FFS) algorithm temporarily closes the canister purge valve for a few seconds and monitors information from the closed loop fuel trim system to calculate the ethanol content. This logic executes several times until the ethanol calculation is deemed to be stable. This may take several minutes under low fuel flow conditions such as idle, or a shorter time during higher fuel flow, off-idle conditions.

Air-fuel ratios and the corresponding ethanol percentage are updated following each purge-off sequence. The fuel alcohol content percentage value can be read on a scan tool.

When an E85 compatible vehicle is built, an ECM or PCM replaced, or if the learned alcohol content has been reset with a scan tool the fuel system will need to contain ASTM gasoline with 10 percent or less ethanol content.

A minimum of 11 liters (3 gallons) must be put in the tank in order for the vehicle to recognize a re-fueling event. It is not necessary to turn the ignition OFF in order to have the re-fueling event recognized, however local safety regulations should be followed.

After the re-fueling event, the system registers the amount of fuel that was added, relative to the amount that was in the tank. Reading fuel trim and O2 sensor activity, the system determines if the fuel added was either ASTM Gasoline or ASTM E85. Based on that determination, the system adjusts to the expected alcohol mix in the fuel tank, and then the fuel trim and O2 sensor activity fine tunes the adjustments. The system must remain in closed loop in order for this adjustment to occur. Numerous short trips after switching from gasoline to E85, or E85 to gasoline, can result in driveability symptoms due to the inability of the system to adjust for fuel composition by not attaining closed loop

So no inline sensor like the 1500 trucks run. It is all an algorithm (the Virtual Flex Fuel Sensor), the EVAP system, and fuel trim monitoring.

Edited August 10, 2016 by 15HDriver

sdeeter19555 · August 10, 2016

So it's the O2 sensor(s) that approximate the alcohol content? Maybe I have one getting lazy...

Sent from my SAMSUNG-SM-G900A using Tapatalk

T-dog sierra · December 1, 2021

Weird problem. The computer starts to drift after a while, I know that much. I was getting mass air and left back/right back running rich error codes. These codes combined with the rough cold start symptoms are indicators of fuel alcohol % wander in the ecm. You need to refuel with 10% ethanol or less in the entire fuel tank and then reset the fuel alcohol% with a scan tool. The ecm will then relearn the percentages and the vehicle magically fixes itself. I changed the mass air and it still threw the same mass air code. I reset the fuel alcohol and everything had been great since. I'm running a 2013 GMC sierra 4.8L V8 E85 flex fuel. I believe this is an issue for all newer(ish) E85 engines that don't have the old dedicated sensor. That New Dude description of the system was bang on. Read that and you'll understand why this fix works. Maybe yours is something similar and a 60 second scan tool reset might work for you?