[st86good]

Hi everyone.
Recently I was feeling that transmission wasn't shifting right.
So I scanned the system with my scanner, and found out that I have one error code.
2E8D DME: Intelligent Battery Sensor, Signal Transmission

Not sure this caused transmission to shift lil weird. Fluid level is correct and filter replaced not too long ago.
Also I found out that I was getting 15.3-15.7v when Idling, and went down to 14.4v, and went back up to 15.3v. It's keep moving.

Engine off, battery voltage was 12.2v. I didn't replaced the battery.

I'm unsure what should I start, IBS? Battery? someone told me just replace alternator but thats pretty big job compared to IBS.

I've saw undercharging battery due to IBS but not overcharging.
Also it didn't came back after clearing code, but voltage is 15.3v.

Might be other symptom but When I start the car, engine makes normal sound, but once the RPM comes down, voltage goes up to 14.4+ and alternator start to make whiny sound. I guess because it is working hard to charge the battery due to bad IBS?

Not sure, I might start to change IBS Cable but any insights will be amazing.