2003 Cadillac CTS shuts off at red light.

Is the red security light flashing? No gas, could be fuel pump or a few other electrical issues.

https://www.google.com/search?q=2005+cadillac+cts+3.6+security+system+reset

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Check throttle body

Need some more information. Do you have a check engine light on? Also, by shuts down, is the engine sutting off when you stop?

Just guessing but trying to help...Your car might be vapor locked..Take off your gas cap... Do you heat KT sucking in air as you take it off...If you do your car will now start...A lot of people at the gas pump will try to get that extra fifty cent in their tank at fill ups..Thats the worst thing you can do. What your doing is putting gas down your gas vapor line...Its meant to burn vapors from your gas tank..When you over fill your gas tank this gas runs down that line into a canister that has charcoal as the filter built inside. Over time your gas will harden the filter to where it becomes clogged..Then as the pressure in your gas tank becomes greater than your fuel pump...Your car will shut off not start back up until the pressure in the tank drops....You can replace this canister... Most are behind your headlights on drivers side..Its that little black box your never did anything..On some vans there underneath...Another thing :is as these canister's go bad your putting all that broke down black charcoal right into your carburetor.. That's those lines thats those lines that are hooked to it at the bottom...So your feeding your car junk...Never over fill your car because in time it will shut off...So just loose the cap and lesson for air sucking in....Try to start it with cap off...More unlikely you have a non stock fuel cap..Either drill tiny hole in the center of cap or replacei it with factory stock...Also some cars have a fuel shut off switch that will shut the gas off in crashes...Sometimes these switches will go bad....they can be reset...Might be in truck under matting....Good luck...Hope all of this helps someone

change your crankshft sensor and camshaft sesor same problem with my moms caddilc cts(and one more thing open your gas cap listen for a hissing sound ..get another person too put the vehicle on on but do not start vehicle.....if there is a hissing soung fuel pump is good)

You should be able to start, what is the fluid level bring it to the recommended level crank it allow the lifter to solidify and compression will build up

my cadillac 2003 had the same problem. my fix was the crank shaft sensor went out. the repair man fixed it for me. but it sounds like the same problem i had. hope this helps..

Hey all. I've had my 2003 in twice for the Crankshaft position sensor. In Feb 08 it fixed everything. My car wouldn't start when it had been running for a while. I'd pull into a gas station, then go to start it again and it would just turn over. Same thing just happened in July 2010. They replaced the crankshaft position sensor again, but now it's still doing the same thing. If I let the car sit for 20-25 minutes, it will start and run just fine. However, this time around the check engine light is on and it has never come on. I'm open to any suggestions as to what to try next. What is the PCM exactly?

My 2003 CTS would not start on the first, second or third try after filling the gas tank. Finally after several months of this occuring every two weeks a check engine light came on. It was the evac purge valve. Tom

the sensor is wearing out, that causes the gas not to back flow, or you need a new gas cap(pressurized). I would get a GM gas cap, because the after markets aren't that reliable for your car.