I know this is an old thread but I am going to post what happened with my car just incase it helps someone. I have a 2010 Forte EX/2.0 engine. I was having issues with it throwing the map sensor code and coolant sensor code. Seemed to run ok and they would clear themselves after a while so I ignored it for the most part. My car was having electrical issues, like sometimes when would start it it the dash lights would be dim and would crank as fast and when it started it ran like crap. And would throw all kinds of codes. And sometimes when you hit the brakes or use the turn signal the radio would cut out. Like some kind of ground issue or something? I ended up putting in a new alternator and battery and for the most part it seems to be ok. Radio still cuts out sometimes which is weird. And I have issues with the battery losing charge but I have been told that is because I don't drive it enough. Like less than 5000 miles in 2 years. I guess driving your car every two weeks or so is that great for the charging system.
So as I said before when it do the hard starting thing it would throw codes like map and coolant. I figured it was the electrical isssue confusing the computer and didn't worry about it. Car seemed to run fine otherwise. And the codes and engine light would clear after a while. Then I started getting the map code and coolant code and the car was actually starting to run a bit worse and getting worse on gas. Eventually to the point it wouldn't idle anymore which made it hard to drive in traffic or in town with it crapping out at every light or stop sign. So spent the 80 bucks on a new map sensor. Changed it out in the autozone parking lot. Super easy to change on my car. Except it didn't fix it. Still didn't want to idle. I looked for vaccum leaks and other stuff but couldn't find anything obvious. And it was giving me the same exact code. The P0106 I think? Something about it not getting a 5 volt signal. I went back in the store and told them it didn't fix it and if they had any ideas. The first thing they asked is if I disconnected the battery when I swapped it out. I said no, I just changed it and cleared the code with my hand scanner. They said that won't work, I have to do a hard reset by disconnecting the battery for 10 minutes, then clear it with the scanner, then start the car. I tried that and it seemed to work. Car idles again and engine light is off. We will see how it goes in the next few days. I am doing a full tune up tomorrow. New plugs, air filter, coolant sensor, clean the throttle body ect.
Another thing to keep in mind is some codes won't clear off the computer instantly and you can't erase them with a hand scanner. I think it is called a "persistant" code or something? You can replace the part and fix the problem and the car will run better but the computer still "holds" code and will show up when you scan it. The only way to clear them is to actually do the driving cycles described in the manual. Some scanners will tell you what that is or you can look it up online usually. Basically for certain codes it won't let them go and will hold them in storage until you drive the X amount of miles or for x amount time for x amount of times. Like you might have to drive the car 40 miles a couple times or make 3 or more trips without the computer sensing that issue. Then it will let the code go.
This is why sometimes you will get a check engine light, then it goes away a few days later. Or why your car will run fine but if you scan it the code will still show up even if the car is running fine.
I will add that I have replaced my alternator, battery and disconnected my battery several times for trouble shooting and I have not had simply doing that cause that code. I suppose it could happen but it hasn't happened to me. For me the code always shows up in conjunction with an engine issue or if the battery drains too low that it won't start or charge with the alternator.
