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Discussion Starter #1 (Edited)
I got an invalid FMM message tonight, which I delayed acting upon. What should I do? I've got 1.8 gallons in the tank right now (as per Voltstats), with the car's gas range only showing 68 miles on the android App.

I bought my car in Dec 2016, eight months ago, purchased with a full tank. I finished burning through that entire initial tank in the middle of May, about 3 months ago, on a road trip that included 675 gasoline miles. So clearly, my average fuel age is nowhere near 1 year old, and it should a bit over 3 months old. During the drive home, I had some engine warning light come on, and Chevrolet replaced the PCM (hybrid powertrain control module), so it is possible something got incorrectly reset at that point. I don't know. Anyway, since May I've burned through another 2.67 gallons of gas including one gallon last weekend, and the tank now has under 2 gallons.

So, I could delay the FMM 24 hours (tomorrow evening), in which case it would probably force itself to come on Monday morning on the way to work. Or I could top off the tank. Or I could let it do FMM on the 2 miles trip to the gas station, burning 0.05 gallons or so. I think I read somewhere on the forum that once you get one of these invalid FMM errors the car will never again use the battery again until you take it to the Service Center even if you fill up the tank. But I don't know. Any suggestions? Here is the thread I looked at but the Op never reported on what happenned: http://gm-volt.com/forum/showthread.php?238889-Fuel-Maintenance-Mode-Gen-2 BTW, it was a fuel maintenance mode message, not an engine maintenance mode message.

update I read in the manual, "... If No is selected, the FMM Request screen will appear when the vehicle is next started... If the FMM request was delayed for one day, FMM will start at the next vehicle start... After FMM has run it is recommended to fill the fuel tank.".

This sort of implies maybe you have to let FMM run before you top off the tank. Maybe just letting FMM run for 2 miles on the way to the gas station would be safer than adding gas while it still lets me delay FMM and run on battery...
- Sheldon
 

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Do NOT add any new fuel until after the FMM has started.

Someone posted a while ago that when their FMM request first appeared, they delayed it for that day and instead drove to the gas station and added fresh gas, thinking it would bring down the "average age" of the gas and avoid the FMM altogether. The following day, the FMM message appeared again, and now they had even more gas in their tank. I seem to recall they needed to visit their dealer service department to have it turned off (I don’t think they tried adding even more gas after the FMM had started, or even just removing the gas cap again and putting it back on). This suggests that once the computer determines the "average age" of the existing gas is 12 months, it doesn’t recalculate that determination until more gas is added AFTER the FMM has been started. IOW, you need to START the FMM before you can END the procedure.

Once an FMM (or EMM) request appears, you can delay it "up to 24 hours" (does that mean 24 hours from the time you see the request for the first time, or until the following calendar day?). The message will reappear each time you start the car that first day, and you can keep postponing it. On the following day it will start without giving you a delay option (Gen 1 will immediately start the ICE, for Gen 2, you need to shift into D). For you, by tomorrow evening you will have no option.

From what you write, it could be the FMM "clock" may have been corrupted when you had that engine trouble. If it’s not working correctly, you may indeed need to have the car serviced. I suggest that after you start the FMM, you could drive to the gas station while the FMM is running and add 2 gallons of fresh gas to the current ~2 gallons. That should bring the "average age" down to ~6 months and end the FMM. If that does not succeed in ending the FMM, then you will need to visit the service department. If it does end the FMM, it would also suggest the FMM clock has been successfully reset, and the next one should occur in ~6 months (or more, depending on how frequently you normally stop at the gas station).

There are many ways to deal with an FMM. I’ve had two with my 2012 Volt and choose to run out of gas before refilling the tank to postpone the next one for ~12 months. Some prefer to just double the amount of remaining gas to postpone the next FMM for ~6 months. Some who rarely use gas like to empty the tank and then add the bare minimum (~1.5 gallons), which also postpones the next one for just under ~12 months.
 

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I bought my 2017 Volt in Aug 2016, was surprised when my FMM occurred in June 2017 two months early. Turns out the car was built in June 2016 and I'm guessing the computer used the day the factory added some fuel before shipping is what it uses to compute when it's due. It ignored the gas the dealer added during PDI in Aug 2016.

I burned mine down to EMPTY (even posted photos of screen messages when the ICE ran out of fuel and I continued on the battery) then added 2.5 gallons and will carry that until this winter and then see how ERDTT uses that.

My advice, just burn it off and add some fresh fuel and manage it going forward.
 

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I'd say don't fret over a few gallons of fuel and let the car do what it wants to do. Alas, I've never seen FMM or EMM as I used to hit the dino juice daily. I now have charging at work, so on most days I can make it here and back home on electric only, but there are enough times where I go out of town, or linger for shopping which causes the ICE to run where I have to add some fuel once in awhile.

This might be a sign that you (the OP) need to get out more. Texas is huge, drive somewhere.
 

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Discussion Starter #5 (Edited)
Eventually the 24 hours ran out. I added 2 gallons of gas this morning, and the Volt switched back to EV mode. The fuel was not stale since I've burned through 20 gallons since the beginning of May 2017. Before the FMM kicked in, I had driven 96 electric miles Saturday and Sunday. But then I had to drive 4 miles using the ICE to pick up dinner; and then another mile this morning on the drive to the gas station. The Volt is back to normal now. As noted, there was a warning light that led to Onstar service after our road trip in May, so that's probably why the computer got confused.
 
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