I replaced the coolant temp sensor on my 2003 wrx. the codes that were showing were a 420 and a 117 code. i decided to take on the sensor first since i had the cads replaced (not stock...my mistake). so i put on the coolant temp sensor and immediately noticed that the temp guage was showing Hot. i burped the system and the same thing. took it to a shop and they ran it through a coolant system diagnostic to tell me that the care was not overheating at all and that it was a false reading. does the temp sensor need to be stock? i got it from an auto parts store. it doesn't make a whole lot of sense to me.