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I just want to repeat what Salman has said in regards to Ford's handling of the issue... especially as we've seen how other manufactures have handled issues. I think its a testament that they assigned a representative to this forum to try and help customers. I say this knowing full well the frustrations of the issue since I had it. It sounds like your in good hands Salman, and I hope it gets the issue resolved, because the C-Max is a good vehicle.

so sorry to hear this Salman :(

Good for you Salman for giving the C-Max another try. That's exactly what I did, and though I've had some issues that required me to bring the 'Max in for repairs, they have all been quickly and efficiently fixed by my dealer. Trading in for another worked out fine for me, but I know how you feel after experiencing such issues and how apprehensive you will continue to be until the new vehicle proves its self. I went through that, and after having it run great for the last year my faith in the C-Max is restored. There is still very little out there that I would buy so I'm still a fan of the C-Max.

Yep, your doing the right thing, in NC you can't pass an emissions test with such a failure, So I had to get mine fixed. Hopefully they get it sorted out for you. Good to hear its not the dealer, was just curious.

When I had the issue on my 1st C-Max, this is what my dealer did, and apparently they saw something, but could not resolve it, which led to me simply trading it for a different one.

I have to echo the question from wab necrochaos? is you're dealer a small one? can you take it to another dealer? I had an Check Engine light indication myself last month, and brought it in, The dealer quickly diagnosed and ordered the part and fixed it. I had to wait about a week for the part, and they did reset the light, but while waiting it came back on the next day. In discussions with friends and the service folks, what I found is that newer cars in general are required to use "smarter" valves instead of more reliable solenoids in much of the fuel emissions systems. according to engineer friends that have worked on these, they said emission laws require feedback that simpler but more reliable parts cant provide, but the short end is your essentially getting diagnostic failure info that isnt necessarily having adverse effects on the car. In old days, once a check engine light came on you might as well call the tow truck as it usually ment you damaged the engine, but now more of it seems to be linked to the emissions diagnostics. Any way, I hope they can figure it out and get it fixed for you!

I've had all the issues described in this TSB and just lived with them. Next time I'm in to the dealer I'm asking to have it done. Thanks for the post!

Yeah... I've felt like a beta tester since my first c-max had the issue in Nov of 2012. Jan will be my one year anniversary of the 2nd max after Ford replaced it. I'm continuously reminded how much I like it when I'm away and have to drive rentals, but I think had I know what I know now, I'd have waited a few years for Ford to Iron the kinks out. Still, I've had no real issues with my 2nd max so I'm happy with it.

There's an FSA/recall now. 13B12 which is out. details are in this thread. I don't know if there is anything different for people experiencing issues, but I hope it helps!

On a whim, I stopped by the dealer to chat about the way the Fuel Gauge works on the C-Max, and while looking for applicable TSBs the rep came across this FSA. Essentially, he said it combines a number of TSBs and is supposed to resolve the issue of modules failing to sleep correctly, and thus draining your battery, but it also was supposed to address window issues some people have been reporting. As an FSA its essentially a recall, and my service rep asked if I wanted to have it done, and did it right then and there. It took about an hour, and I had nowhere else to be at the time so I had them do it.

Thats exactly what I'm seeing jmckinley!

My understanding is that there is a fuel gauge, which you can read how they work here . Essentially though, the gauge uses a float that is wired to a computer. If the C-Max is strictly using this to compute the MPG, then there certainly can be inaccuracy, especially if your topping off, because, as shown in the animation in that link... the float will be submerged and won't move until you consume some fuel, thus it will effectively consistently under report the fuel consumed, which is exactly what I'm seeing. However, I thought that the C-Max (and more modern cars) actually computed the volume of gas consumed using a different gauge which was part of the fuel injection system. These gauges count the duration and number of injections and can compute volume that way. I'm pretty sure the float gauge is whats used to give the basic fuel gauge fire the "empty" light, but I would have thought that the other gauge would be used to compute the actual MPG. Of course I'm no auto mechanic so I could be completely off base.

As someone who has been following/posting on this thread since page 1, I have to say it is a bit disheartening to see the core issue hasn't been solved yet. I think Edmunds summed up my feeling when I 1st got into my C-Max... And I still really really like my C-Max. Ultimately seeing this issue drag out confirms to me that the C-Max electrical design/Build is marginal. It seems that if you get one that works your good. I see this all the time in control systems where a part is selected and built into a design and it works great until the part manufacture has to change it slightly, and though its with-in its own spec, it pushes the aggregate design up to or just over the intended design limit causing intermittent failures. This was ultimately the deciding factor for me when Ford couldn't fix my 1st C-Max and offered to return it to the factory and repair it. I think their are a set of people whom Ford has legitimately identified the problem and fixed it for them, e.g. dash issue or a wiring harness issue, but I still not convinced that their isn't some other issue either with the way certain parts work in the aggregate or just the way they are assembled. The complexity of different systems in different models doesn't make it any easier for Ford to find the problem, but since, as its been pointed out, the issue seems to effect all models, one might think starting with the simplest and solving the core issue there would lend to resolving the others. On this Thanksgiving day, I think I'll be thankful that my replacement C-Max has been functioning exceptionally well, and hope that for those still fighting the issue... it gets resolved for you.

Thanks for all the data folks. PtJones, I guess I too am interested in finding out more about how the "Smart" Gauge works, as I would assume (and it sounds like in correctly) that the a gauge would want to accurately report volume. I guess I'm not understanding what or why knowing the "energy content" of the gas is needed to make a calculation for the MPG or any of the trip information? I've concocted my own experiment... and I guess some members can tell me if they think this is flawed... Upon the car notifying me that the fuel is low, I promptly (with-in a few miles) fueled up exactly 10 gallons. I'm interested to see how close to 10 gallons it will be when I refuel again. My assumption here is that the refuel light/gauge comes on about the same time each time. I'm also assuming that is a different sensor than the smart gauge used for fuel calculation. I don't think it'll be dead nuts accurate, but I would expect to be able to be with-in a tenth of a gallon accuracy. That would be it working. What I'm hoping to prove or disprove here is that when I fill up and top off, perhaps (as suggested) as the fuel warms up and expands, i'm actually loosing some to leakage? I would have assumed that the tank was supposed to be a closed and sealed system as some states (like California) have laws that are supposed to prevent fuel spillage, but maybe something is wrong and the capless system isn't sealing right? Anyhow, Since I'm not topping off, that should remove that variable, and it'll be interesting to see how close to 10 gallons the trip gauge says I am when the refuel light comes on. Of course, I'll probably need to do this 3 or 4 times to get some trending data. And Happy Thanksgiving everyone!

HPRifelman, that's nice data. but that's not at all indicative of the data I'm seeing. I'm never seeing a positive difference. I'm always seeing between 3/4 of a gal and 1 Gal negative amount. Also... I've had the luxury of having two c-Max's (I jest because one was lemoned) and both behaved this way... never once reporting a positive difference, only negative. Also... gas pumps are actually calibrated and certified to pump the correct amount of fuel. Saying that all pumps are that inaccurate is a stretch. It doesn't add up to me. Obob, I think you have an interesting point. There should be an easy way to test that idea. I think your suggesting that filling up in say the peak of the day when its warmest, should result in a positive difference since the fuel will expand so it takes less to fill up the same volume. The thing I would counter is that fuel tanks are buried and the temp of fuel that is pumped doesn't actually change dramatically, thus the argument of fuel expanding or contracting seems to be a dead end to me. Since pumps are strictly calibrated and tested to meet those standards and the fuel doesn't actually expand or contract as much as people may think, I'm still highly skeptical of the way the car is actually calculating the value. More so, I find it odd that after the firmware upgrade it went from being 1/2 a gal off to 3/4-1 gal off.

I've used pure gas and my results are the same. The amount of energy in the gas shouldn't make a difference. Its a simple calculation of Miles divided by gallons. If you use gas with lower energy you should simply go less miles for the same number of gallons. I guess the issue is actually the gauges according to this article http://www.edmunds.com/fuel-economy/your-fuel-economy-gauge-is-fibbing.html If this article is to be believed, the gauge counts the number and duration of fuel injections and makes an assumption of the volume for each injection, and it seems they are all off because 92 percent of cars use the same gauge. But since mine went from about 4% to 8% after the reprogramming, I think they certainly can get it closer to accurate.

Ok, this is probably the issue right here. Most gas tanks will typically hold more gas than the rated capacity. Thus, if the rated capacity is 11.5 Gal and I'm sticking 12.5 Gal in it the computer will mess up. Sounds like I need to run an experiment where I pump it up to 10 Gal, and then when it says 10 Gal is consumed, pump ten more and do that several times to see if its accurate that way. in otherwords, I'm wondering if over filling could cause the issue? spyburn... thats just odd... don't know what to say about that.

See this is where I'm at a loss. You can talk all you want about how testing is done with this type of gas or that the clock is running when the engine isn't, but the basic premise of calculating MPG isn't all that complex. I mean its literally the number miles driven dived by the amount of fuel expended. So if the number is wrong, then either the car is miscalculating the miles, or its miscalculating the amount of gas expended. Its seems from other threads the Millage has been shown to be pretty close via GPS (with-in 1 or 2%), so that means its likely that the fuel expended is wrong... putting aside some other simple issue like a crack in the filler neck. From what people say, the sensor on the fuel pump is pretty accurate. Like I said, most of my cars in the past have been pretty basic, I guess I'm just astonished that something so darn technical and complex as this hybrid car can't get something that seems pretty simple, like accurate MPG to work correctly?!

Interesting ptjones. I guess I don't buy that many cars. My last car was a Nissan 350z, and it was always dead nuts on. Most vehicles I owned prior to that one didn't have electronic trip computers, so the 350z is my only real data point. It seems to me that they should be pretty close. Maybe I'm expecting too much?

Good idea Dave. I'll do that.

Ok, nice to know its not just me. To me it seems like a pretty simple process. From what i've read the fuel pump is pretty accurate, so the computer knows exactly how much fuel has been consumed and it should know the mileage.... though I guess its under reporting that by 1.5%?? But that 1.5% might adjust your MPG by about .5 MPG is all. That would more ignorable than 3-4 MPG I'm seeing.

Yep. I would say I might have seen a modest (1-2 MPG) increase since the upgrade, however, It reports 46-47 MPG now when its really only getting 43-44 MPG, which is off by 3-4 MPG per tank! I'll probably call the dealer and ask if they can find any TSB, and then maybe call the Ford customer Service and find out if they have a solution. I'm sure this will be the 1st time they've heard of an issue ;-)

For experimentation purposes, I have attempted to use the same gas station and the same pump. that aside, all things being equal, if it were the point of pump shut off, one would think sometimes it would over report and other times it would under report. I have considered that if the seal of the "capless" tank were bad that maybe I'm loosing gas due to evaporation? But 1/2-1 Gal of gas evaporating seems like allot too! It might seem picky, but when I owned a 350z, that thing was always dead nuts on about the MPG and gas usage. I find it odd that c-max can't report it correctly!

thanks Salman, I'm sorry to see your having to go through this process, but I think the laws to protect the consumer are better in California (at least thats my experince having lived in California for about 10 years) so I expect you'll be treated right. To answer your question. Yes, in NC even after all the criteria have been met, you still have to notify Ford directly and give them that opportunity. I was a bit confused about it for my case, and when I finally demanded a buy-back, the Ford service representative actually invoked the "we have the right to attempt to repair it one more time after you notify us in writing" clause. This could have been a time consuming mistake on my part, but when I talked to the dealer they informed me that they would simply do an administrative "in-and-out" and sorry to Ford we can't fix-it deal, and I had to get the proper paper work to Ford, which did delay everything by a week. By that time the dealer was firmly on my side and wanted Ford to do the right thing also. So it ended up well, but non-the less, had I done the proper notification directly after the 2nd time, when the 3rd time happened it would have been quicker.

I noticed that my MPG was off by about 1/2 a gal (actual) when I purchased my c-max. But since I had the efficiency upgrade done to it last August, its now off by about 1 gal actual. What I mean by this is the reported gallons used for a tank of gas by the trip meter (resetting it when I fuel up) may say 11 Gal, but I have to pump 12 gal to fill it up, thus lending to difference between the actual and reported. I'm pretty sure others have seen this, and I'm wondering if anyone has reported it to Ford, or if there is a TSB that would get it closer to actual? While its nice that my C-Max says its getting an average of 46-47 MPG, I know the actual is closer to 42-43 so its over reporting by almost 4 MPG.