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Are you sure about the antenna? The 3G models use an internal antenna while the 4G ones require an external one. I believe a few people have been 'successful' running without one to some degree but it really works best with an external antenna and the official Ford service docs for the upgrade include that and the appropriate OEM antenna with the process. If you don't have an external antenna attached, this is one I personally use and I believe early on it was linked to by a number of people doing this upgrade: https://www.amazon.com/dp/B07PFLWY77 The only caveat is that will throw a code on the TCU about a circuit/ground issue on the antenna but otherwise it appears to be harmless and works fine.

What system? Is it the 8" touch screen or the 4" non touch screen. Portions of your post hint at the latter. Unfortunately it seems like those systems are a bit more problematic. I'd try first pulling fuse 67 (not to be confused with fuse 79) which is for the Sync system itself. 79 is for the ACM which is a different set of issues. See if that brings it back at least temporarily. If not, you may be looking at hardware failures which is not uncommon with those. Most people just go to aftermarket headunits with those. It's often not worth the limited functionality the basic Sync system provides on those and having to pay the cost and risk it going out again. The 8" touch screen systems are a whole different beast. Usually Sync 3 units (2016+ model years) are rock solid. Older Sync 2/MFT hardware (2013-2015) is pretty ok especially once they're fully updated. Some hardware failures exist but aren't nearly as common. These are also easily upgraded to Sync 3 which I personally highly recommend if you can afford it. You get the benefit of a newer more reliable infotainment system and added Android Auto/CarPlay functionality from a fully OEM/integrated system. And it's virtually a plug and play upgrade. Semi-related comment: But for people shopping around for these vehicles, one of my main recommendations is going for one with the 8" touch screen infotainment if possible. Sounds counter-intuitive but they've gotten more attention and fixes over time compared to the 4" models.

Just taking a wild guess here: Do you have the 4" basic non-touch screen system or the 8" touch screen? For the 2017 hybrid SE models the latter was available as an option, not standard. If you do have the 8" touch screen, can you confirm with the images linked below if yours looks closer to Sync 3 or Sync 4? https://api.mss.ford.com/dbi-kb/api/knowledge/v1/search/get-drupal-file/sites/default/files/2024-10/Ford SYNC Visual Reference Guide English_0.pdf If closer to Sync 4, that's Sync 3.4 for our vehicles. The previous owner would have manually done that upgrade as Ford doesn't officially sanction or offer it themselves. One thing that is 'broken' is the flickering screen when the brightness changes. But it's more a rapid flickering. ----- Beyond that guess, another thing you could try is seeing if the behavior changes with different headlamp switch positions (try them all: Off, park lamps, low beams, auto). Also checking Forscan for any codes may also be worth trying as long as you have an MS-CAN capable adapter as anything related will likely be on that bus.

For me I've basically skipped refreshing the included tire kit/inflator. Ulterior motive for that being I found mine had an air leak somewhere and wouldn't get up past around 20 psi. Instead I just got a cheap tire inflator from the local big box store. Slime branded model that also has a digital pressure readout and auto-stop once it reaches your set pressure. Then just a simple tire plug kit to go along with it. Both are small enough to stash under the lip in the cargo area on my Energi and the old space under the passenger seat is now open for extra storage.

The EV miles is likely because the dealer reset the whole vehicle when you requested a 'reset' and it needs to figure out the real mileage again. The 12v battery won't have any impact on that. Real world your EV range is not going to change. But yes, I don't trust most dealers or independent mechanics to know to do the lifetime reset. Pretty much anyone who has been in the community long enough recommends owners to do it themselves after a battery replacement no matter if the mechanic/dealer said they did it or not.

I may miss some questions, but will try to cover everything: There's no conventional engine starter on either the hybrid or Energi models. The engine is cranked by the starter/generator motor in the transmission as part of the hybrid system and is directly powered by the HVB. The 12v battery is just used to wake up the various computer modules and activates the HVB contactors so it can take over. But it still needs beefy cables as it still has other sizable 12v loads no different than a traditional ICE only vehicle plus additional unique 12v loads like the electric power steering, electric water pump, etc.. The DC-DC converter takes place of a traditional alternator, converting power from the HVB down to the 12-14v to charge the 12v battery and provide running power to all the 12v systems. It is capable of providing up to ~140 amps of power and is programmed to behave like a traditional alternator in many respects. It runs at all times when the vehicle is running even when the engine is off. Much like an ICE only vehicle, the 12v battery should be able to be sufficiently maintained under normal driving conditions, even without plugging in, as long as you don't drive super short trips constantly. The HVB is able to be charged in a number of ways: Via plugging it in for Energi models or via regen braking or the engine directly charging it while cruising. Regen can happen while actively braking, coasting, or using cruise control/hill descent control. Any time you see the upper arrow on the gauge in the cluster (I am not sure if the 2014 models still had this. Ford removed it in some later model years), charge is going back in. HVB charge level does not impact the DC-DC converter in any significant fashion that I am aware of. For Energi models while plugged in and the HVB is charging, the onboard charger, separate from the DC-DC, will provide a minimal amount of 12v support to keep the car awake during the process. Once the HVB is completely charged, it will top up the 12v battery before putting the vehicle to sleep completely. No further 12v battery maintaining will be done in this state until the vehicle is woken up again (ie: Locking/unlocking, opening a door, etc. when everything begins to light up inside) The 'second battery gauge' is simply showing the hybrid portion of the battery charge. There's only one single HVB and it is software segmented between of the plug-in charge and the depleted hybrid only operation. Once the plug-in charge is depleted and that second gauge shows, it will fluctuate up and down normally as it is driven and normal charge/discharge cycles happen of the HVB. When in this depleted charge mode, the 'EV Auto' mode you're stuck in behaves the same as EV Later. The brake pedal is specifically designed in these vehicles that under light application it does not put pressure on the friction brakes but engages regen at various levels depending on pedal pressure. The further the pedal is applied, you start physically applying friction brakes as well. Low gear just engages extra off-pedal regen. Unlike an ICE only vehicle, it will not affect how the vehicle operates while accelerating. It should NOT be conflated with one pedal driving for a few reasons. It will not bring you to a complete stop on its own. Regen effect will start to taper off down under 5-10mph. Also the brake lights will only activate with the brake pedal applied. Using cruise control and hill descent control (The button on the left side of the gearshift) will also apply regen in their own way. Cruise control will maintain speed via deceleration as well as acceleration. Under decel it will focus on regen as much as possible and has methods to bring in full ICE based engine braking and the friction brakes if needed. Hill descent control will try to keep you from gaining speed downhill with no throttle/brake applied, even without cruise set. Similarly, it will use regen as much as possible.

There is a coolant temp gauge under the MyView screen. It only tracks the ICE/cabin heat coolant, not the hybrid/inverter side. It also is not a 'dumb' gauge like most vehicles and will gradually move based on temperature which is nice! Beyond that, I'm not aware of any other relevant gauges. Mostly all the EV vs ICE usage, auxillary/HVAC power consumption, etc.. There are one or two pages under MyView that will track the ICE tachometer as well. Oil pressure specifically is definitely not covered stock and not 100% sure if there's a PID for that for aftermarket units but I can double check later this evening. I know on some past vehicles I've owned they have not tracked oil pressure so I don't consider that one a guarantee.

As far as the 2016 situation, here's the gist: 2016 model year C-Maxes with the appropriate trims/options (ie: Has the 8" touch screen, not the 4" non-touch unit) would have been supplied with Sync 3 vs Sync 2. But the USB hubs in the center console were not compatible with CarPlay. I believe something to do with a special identification chip that Apple requires. Don't quote me on that though. Android Auto users don't have the same issue. But 2017+ model years they updated the hub so it is compatible. There was also a software update to Sync that was needed too. Many may already be past this. Always recommend to go through Ford for these updates first and it'll get the software side sorted out: https://www.ford.com/support/sync-maps-updates/ . Some suggest using Cyanlabs to get to newer 3.4 versions that Ford doesn't officially support on our vehicles but it requires some technical experience and has the potential to brick your APIM. If you happen to still have an older hub and update Sync 3 to the latest available version to you, you should then receive a warning on startup about USB hubs not being supported. The hub replacement is inexpensive and quick to do. The hub in the center console just snaps in. Pop it out, there's two connectors on the back. Unplug the old, plug in the new, pop it back in. No further work or programming needed.

On Sync 2 that's just Siri but not CarPlay. CarPlay is specifically the full screen takeover of the infotainment system which is only accessible via Sync 3. Yes, the upgrade does require a bit of hardware swapping but all the kits being sold include everything and are usually plug and play. Doesn't require much technical knowledge. Just make sure not to buy from Chinese based sellers (They often bodge together APIMs which may brick easily if you try to update/reset/reconfigure them) and ensure they ask for your VIN for programming as that is needed. DO NOT agree to have someone remote in to your own PC to do the programming. Huge security risk and not needed at all. All reputable sellers will do the programming based on your VIN before shipping out. We had a user in the /r/cmaxhybrid subreddit mention these shenanigans going on. Here's a tutorial video I always refer folks to. It's for the Escape but all the components and locations being worked with are identical to the C-Max:

This is what Ford used to call the 'oil maintenance mode' on earlier model years and changed it up to this confusing wording later. This mode only exists on Energi models and will run if you have too many drive cycles where the ICE starts but runs in short bursts or otherwise doesn't come up to full temp. Many will see this during the colder months of the year with cabin heat being used especially if you stay on EV Auto mode. It's normal and it is designed to run the ICE full time until it gets hot enough for long enough to boil off accumulated moisture in the oil. It'll continue to run even between vehicle restarts until it is satisfied. A quick way to end it is to get on the highway and drive it for a bit so it is under a consistent engine load and maintains the coolant/oil temp it needs. Just keep in mind that once it finishes, it'll drop back to 'Auto' operation and with plug-in charge available that means it'll be running on EV power primarily and you'll want to switch back to EV Later while still on the highway to help protect the battery.

You need to elaborate by 'strange noise'. The electric vacuum pump for the brake booster on these vehicles is quite audible and normal. It may also activate periodically during normal brake application as the vacuum in the system is depleted. Run time during each occurrence can vary but may last a few seconds. If the system fails or cannot sustain proper vacuum, it monitors this and will throw codes and drop you back to hybrid or full engine operation so the engine can provide vacuum as a failsafe.

Just as a fun little added tidbit. I ran across this post a while back and a cool video to watch to see how these things 'crank' the engine over: Per the OP it's a Nissan Altima hybrid which has an eCVT just like ours. Spark plugs are all disconnected there in the video.

Maybe, but I'm doubtful. It'll know if it has enough charge in the HVB to start the engine successfully. If there wasn't, it wouldn't even get to the cranking stage. And these have enough oomph to get even a stone cold ICE started. You're talking a nominal ~300V battery pack with gobs of amps vs a ~12v lead acid battery starting an ICE only vehicle. Hopefully it is something simple on the ICE side like fuel/spark/throttle body. But getting codes read first is really the best first step. Without any kind of diagnostic tools available, you're merely guessing. And you can't afford to continue trying to start it and drain the HVB further.

Based on the low RPM, I'd say it isn't able to successfully start the engine and is failing out for some reason. It may seem like the engine is running, but it's not. It's just with it being cranked by the hybrid system it feels a lot smoother than a traditional ICE vehicle. Being a hybrid vehicle, I'd IMMEDIATELY stop trying to start it as it'll continue to drain the HVB until it can't be used any further and you'll be stuck with a dealer having to bring in a charger to bring it back up which will cost $$$. No way to DIY it yourself at least safely. Get codes read and see what the vehicle is reporting. If you want to see a good example of what a 'no start' condition feels like, here's a good video. It's from an old Escape hybrid but the systems are nearly the same:

To be clear: The BMS only needs reset if changing out the battery. If you're just disconnecting the same battery for some reason and reconnecting it after, there should be no reason to reset the BMS. That's all retained in non-volatile memory that doesn't get affected with loss of power. Also the BMS reset can be DIY'd. The best solution is to use Forscan (either the mobile or PC version, both have the necessary service function) with your OBD adapter of choice. There's some method floating out there of doing a whole dance with the high beams or flashers or something but the issue with that is there's no clear confirmation that it succeeded. With Forscan you can check the battery age PID after the reset to confirm it took.