Wow, My 2002 Ford focus' check engine light came on just today! I still do not know why! I checked my oil (which was changed last month) the trasmission fluid, made sure everything was tightly screwed on..... NO CLUE!!! Id say your best bet will be to do hat I am gonna do tomorrow and take it to Auto Zone or Advanced Auto and see if they will do an OBD reading on it...
That means that rad. coolant is leaking into the combustion part of the engine, and burning, thus white smoke. Most likely the head gasket has to be replaced, and have the head checked for cracks also.
It might be the catalytic converters. My 2002 had the check engine light on and it was a bad cat.
Check the hall sender on the distributor, you can check at the coil connector using a led, it should flash when cranking the engine. After that it is most likely the coil.
Have the fan motor checked to see if it's getting power. If not,then it will need to be replaced.
Faulty sensor get it replaced if not check to make sure wire isn't shorting out
Have you checked the handbrake or the engine temp.
It would help to know what model and year the vehicle is, but the first thing that occurs to me is a poor electrical connection, especially grounds. Trace the ground cable from the battery and insure that all connections to the body and engine are clean and secure. On most cars that I work on this amounts to four or five connections in the engine compartment. Also anytime the check engine light is coming on, have it checked for codes.
If it has the 4.3 ltr engine, the intake manifold is notorious for leaking at the back of the engine where you cannot see it. Try using a mirror at the rear of the intake manifold and look for wetness. Replacing the gaskey is the best fix.
Could be a problem with the wiring from the computer to the sensor.
If it is clean, undamaged, and in good working condition.....NO. Since the radiator needs to be removed, to remove the engine, now is a good time to have it cleaned and checked.
Seized engine? Loose or corroded battery cables? Weak or dead battery? Bad starter solenoid? Bad starter? Bad clutch or neutral safety switch? Bad ignition switch?
Hummm.... Tough one. I would carry it by one of the parts store that will read the code for free. Autozone is one. If you have the code, you can find out whats going on. Wish I could tell you more.