Prius hv battery maintenance ( check hybrid system )

So my prius check hybrid system came on and I took it to the dealership and was told that the hv battery need to be replace. I decided to do it myself because I have some basic knowledge and working with electronics. So after watching a couple of YouTube videos I took out the battery and began to test it. I already bought a cell module online. but my problem was all the tested out good all showed above 7.7 volts. this left me stuck cause I was expecting a bad cell. I even tested by pair getting around 15.5v.

the only thing I could think of is the fan because it was extremely dirty but can that cause a check hybrid system and give the code bad battery pack?

 

Well here an update, today has been a long day. I did more testing on the battery and I still couldn't find nothing. I used my subwoofer to do a load test (only thing I could find) 2 min on each module, all of them pass. So i gave up on the module. I was left with just cleaning it..... and here where things went bad.... I broke the fan. I had the fan in my hand using a compressor to clean it. when I went to pull the trigger to blow the air, I forgot the compressor was turnt all the way up and poof it flew out of my hand and on to floor breaking 1 of the screw mounts holding the motor. I glued it back together hoping that all that happened. now i went to clean off the nuts and bus bars on the battery. when I was putting the nuts back on I over tighten one and broke one module... I know im full of fails... so I ended up using that spare module I bought. But it was ok because it made me clean underneath the module which was extremely dirty also, but WOW it pain in the nice person to put those modules back together. I put the battery back in and drove it for about 2 hours and no message or lights came on...... so I guess It was because it was dirty causing the check hybrid system. now that makes me wonder why the hell didn't toyota put a filter for hv battery...