Code 14 & 53 '91 GP

Came home tonight, when I parked my car ('91 GP w/ 3.1) it stalled at idle and set a code 14 (coolant temp sensor) and a 53 (voltage greater than 17.1 volts at ECM terminal B2 for 2 seconds). these codes set simultaneoulsy. Can anyone shed any light on what may have triggered these two codes? Could a failed coolant sensor cause a voltage problem at the ECM? The Alt. was replaced about a year ago with a new Delco, I haven't ruled it out yet, but it seems okay. This car has been a huge pain in the a** lately, any help is very much appreciated! :banghead: Thanks.