This afternoon I drove about 15 miles to my parents house.I parked on the drive and did the usual cooling down stuff. About 20 minutes later I started the car to go out and the check engine light was on. After nipping out for a short while, we went back and I connected up the black plugs under the dash. Codes 21 and 22 came up which were the engine coolant temperature sensor and the knock sensor. I looked around for any obvious reasons for them alarming, ie damage and couldn't see anything. So next I reset the ecu.
Having now driven 15 miles home the lights are out and she's running perfectly. Does anyone know why the CEL may have come on? My initial thought was maybe a bit of knock on start up due to the engine being hot and fuel vapourising in one cylinder? Any help appreciated.

 

had code 21 come on my 95 wrx, the first week or so it would come and go intermitantly, clearing after a reset. Eventually it caused the light to stay on all the time, had the sensor replaced (not an expensive job in my case) and no prob since, one code might of triggered another, I aint no teccie but somebody will know for sure m8