Take it to your closest auto parts store (If it is a 1995 or later) and they can run a diagnostics on it and tell you exactly what is wrong. The service is also free of charge.
your engine is stuffed
yes
With the proper scan tool.
Check this site for information: http://www.troublecodes.net/Subaru/
why the engine light of my subaru came on after i washed the engine
Not necessarily.
If you take your subaru to Parts plus or an automotive store you can usually have them hook up their computer to the side panel, in the dash board of your car and it will give them a code. The code will tell you exactly why the check engine light is on.
Most auto parts stores have a check engine light reader that you can borrow for free to read the code and also to reset the check engine light. If they are not busy, they may even do it for you for free. Support your local parts store! Worst case: Take it to your dealer or buy a check engine light reader that can also reset it.
After repairing the cause of the code, you can clear it with a scan tool.
take earth of batt for 5 mins an then put it back on an it resets it
make sure when putting gas cap back on that you tighten the cap until it clicks or the check engine light will ccome on
It is possible that a Subaru Check Engine Code #12 is a bad starter switch. This is usually the starter relay switch malfunction code for Subaru.