I have a 2010 Honda fit. I just changed my transmission fluid. I'm having the following problems after he was running fine before. The transmission refused to shift gears. Without releasing the safety release on the shifter. The OBD connector port it's not connecting. The power steering started working intermittently. The battery is not charging properly either. I checked the battery ground.. Going to reseet the brain connector. I believe it is ground issue.

 

These problems sound like a bad battery connection to me also. This many things affected after a simple trans fluid change sounds like they may be coming from a single source/ problem. When you changed the trans fluid, what else did you touch under the hood? Is your car an automatic or a stick? By chance did you remove the battery to access the automatic trans filter located externally above the trans and under the battery?

I'd start by closely examining the battery cables looking for corosion or loose/ broken battery cable ends. Grab the battery cable ends, one at a time, and try to rotate them on the battery posts. I've found over the years that some Honda factory battery cables, when tightened as tightly as they will reasonably go will at times not be tight on the battery posts. The cable won't tighten any more, and looks tight, but in fact will still be loose. Part of the problem I believe is slightly undersized battery posts on some replacement batteries. Other times factory battery cables can be over-tightened and the cable ends will crack etc, and leave a bad connection.

There is also a grounding terminal under the battery box where Honda designed a common grounding spot to ground electrical circuits. Make sure there is no battery acid corrosion or rust on this grounding spot.

 

If the positive + battery clamp does not tighten completely, you may simply need a thin lead battery terminal shim such as this. You can find these at auto parts stores

 

Discovered that the alternator is putting out low voltage. Going to recheck belt tension. Belt tension seems correct. Also going to brake light switch and shift interlock as well.

 

Glad you found the problem. Six months ago I replaced the alternator on our 2012 Accord EX 4 cyl. If you're headed in that direction of replacing your alternator, I'll make a couple of suggestions. Replace the alternator with a quality rebuilt and consider a replacement oem serpentine belt at the same time. Depending on mileage on the car, also consider replacing the serpentine belt idler with an oem replacement. I suggest oem parts for the belt and idler only because of the oem quality and the hassle of taking everything back apart if inferior quality parts are used and fail. As far as the alternator, it may or may not be available new, but will be cost prohibitive. A quality major brand rebuilt is the next best option.

 

Have decided to rebuild the alternator. The auto electric shop told me that the Denso rectifiers have problems. He told me that there replacement rectifier that has diodes 50 amp instead of the 30 amp that are standard with the Mitsubishi alternator.