What part of the MacBook Pro 13-inch 2.4 GHZ (Mid 2010) logic board is what sensor? My MacBook Pro 13-inch 2.4 GHZ (Mid 2010) starts up normally but after approximately one minute the fan accelerates and the system slows down dramatically. The CPU load goes up to 99% as I see it on Activity Monitor. The laptop is running without battery as it suffered a water spill some months ago. There is no virus and no other process is using large amounts of memory. 

The problem was thought to be linked to a DC-in board that I replaced after the water damage. The DC-in board was working fine and the input voltage is approximately 16v as seen on a voltimeter. Apple Hardware Test gives me this code: 4SNS/1/1C0000008:TN1D--124


How can I check what part of the logic board is what sensor?
If there is a faulty temperature sensor on the logic board how can I find it and replace it using the above code?
This issue is definitely related to the logic board. There is definitely damage to the board from the liquid spill and likely ESD damage from when you replaced the MagSafe board. 

There is no supported way to replace or find a temperature sensor on your model MacBook Pro. In order to replace a sensor on one of these boards you'd have to solder off the old one and solder on a new one. Since no one sells temperature sensors for the boards that integrate them, it would be a nearly impossible feat. 

I'd recommend taking it to the Apple Store or an Apple Authorized Service Provider for a full repair. They may not be able to service it since you've serviced your own machine.

I know this isn't the news you were hoping for, but I hope it helps.