My 2003 cadillac deville-the service engine soon light came on and stayed

Disconnect computer for about five minutes,if that doesn't work check all the fluid caps!

Cadillac codes are easy to read..then replace the bad sensors etc and then clear the codes and try again etc

The service engine soon light indicates a problem.
Take the vehicle to AutoZone and have them read the computer code.
They can give you an idea of what the problem is and reset the light for you.
BTW the service is free

Service Engine light just is a warning that is time to tune up or change fluids. Isn't the same that Check Engine light, this is some fault code stored in the PCM and will need scanned to know what sensor is in fail.

Good luck.

There is a reason that it came on. Something has malfunctioned (usually an emission control device) to casue the light to stay on. A trip to a place like Auto-Zone or O'Reilly's can get you the FREE use of a diagnostic tool to reset the light. It also downloads the codes to tell why it was set in the first place.
Good Luck

Subject:
Service Engine Soon (SES) Light On, Diagnostic Trouble Code (DTC) P0741, Torque Converter Clutch (TCC) Excessive Slip, Transaxle Chuggle, Slip/Surge (Inspect/Replace Internal Transaxle Components) #04-07-30-034 - (08/06/2004)
Models:
1998-2002 Cadillac Eldorado
1998-2004 Cadillac Seville
1999-2004 Cadillac DeVille
2000-2003 Oldsmobile Aurora
there is a write up on this about 3/4 page down.

http://www.cadillacforums.com/forums/cadillac-forum/t-107360.html

you can try taking the positive cable off for about 3-secs and check in you owner manual to see if it tell you how and if you do have one try this website www.edmunds.com to see if you can download one for you car.

put a new gas cap, those system are pres. even if
the cap look ok it maby leaking replace with a new
one it should solve your prob.
eng.ligh come on because of the gas cap

SERVICE ENGINE SOON and SERVICE ENGINE NOW are 2 amber warning lights pertaining to the vehicles computers.SERVICE SOON advises you of a problem, although not an emergency should be attended to promptly. Your technician can trace the problem by accessing fault codes through the climate control panel. SERVICE NOW indicates a more severe problem which will most likely precipitate a failure / breakdown. The CHANGE OIL LIGHT indicates by time and mileage is a separate light.

The warranty company was able to find a used transmission for $900 which was still under warranty and it will cost 11.5 hours for the install, plus shop supplies and diagnostic. Total cost about $2000. I drove the car for probably at least 10,000 miles and it was leaking a small amount of transmission fluid even after I fixed a seal (waste of money) before getting it fixed. I didn't see the fluid though on my garage floor though as there is something that would catch it.

Cadillac dealer stated this is a known problem with the clutch assembly and that there is a bulletin out on it. The reason the car stalls is due to the transmission not the engine. When the car is at a light or the like there is apparently too much strain from the tranny and it stalls the engine. My car didn't get that far, but after reading a bunch of stuff and looking up the codes it appears to be the case. Of course you could get lucky and the solenoid is just bad, probably not though due to the bulletin.

You can read the codes and clear the codes easy enough. If you don't know how there are many posts on the net.