To correct machead3's answer: 4SNS is not specific to a temperature sensor but can either be a current (I), voltage (V), or temperature (T) sensor issue. In this case, we have a current sensor since the identifier starts with an I. You can read more about it on this great CNET article. The article goes onto say that the second letter identifies the component. P, in this case, is associated with the "power bus", meaning there's an issue with a over or under-current somewhere in the power bus.
I am experiencing the very same issue and this is as far as I've come to troubleshooting it. What's eerie is that my computer also exhibits the very high kernel task which is making me think a low-level interrupt handling is hogging up all the CPU time. My computer will only boot up if the power button is held down and the chime is allowed to play, otherwise the sleep/power light briefly turns on and then off again.
My problem came about from liquid damage so I am going to try an isopropyl alcohol bath tomorrow to see if that alleviates the issue. I also suspect that the 'B' in 'BR' stands for battery. Perhaps the R stands for rectification? I don't know. I will update with my bath results as soon as I have them. Hopefully I am able to cut someone's troubleshooting time as I've been struggling with this all day.
Update on my problems: Culprit was an incorrect current reading signal (Charger BMON according to iStat) coming out of the battery controller. The signal comes out the controller and into the SMC through an analog MUX. In my case, a mid-2012 15" MacBook Pro, the battery controller IC is immediately above the battery connector and the SMC is on the opposite side of the logic board to the left of the same connector. Not only did I give the entire logic board a 99% isopropyl alcohol bath, but I also paid special attention to the two ICs (battery controller and SMC) and their surrounding areas/components by using light strokes of a small paintbrush along with the same alcohol to remove foreign contaminants. My MagSafe DC-in board was also given a thorough cleaning.
After my initial clean, the laptop ran without a hitch. However it shut down unexpectedly maybe an hour after. Running another hardware test revealed that there was still some trouble with the signal so I went in to clean it again. The unexpected shutdowns were accompanied by the following message in the console when booting up afterwards: "kernel: Previous Shutdown Cause: -79". After some digging I found out that -79 meant an incorrect battery current reading, so instead of there being a constant problem with the signal it was now intermittent (perhaps due to the heat of the computer loosening up some contaminants or through jostling of the laptop). After a succession of cleanings I no longer get the error or unexpected shutdowns.
I managed to find a schematic for an older A1286 MacBook Pro model which gave me some insight into how the charger controller was interfaced to the SMC. The shutdown cause was determined through an Apple service manual for the mid-2009 A1286 MacBook Pro model which was found doing some Googling. A list of shutdown cause numbers and descriptions on page 37 under the intermittent Shutdown heading. This list is omitted from newer service manuals or I did not look for them thoroughly enough.
In any case, I am updating from the same laptop and I haven't run into problems since. I hope I am able to shed some light on similar problems for someone else in the future!