2000 Saturn S-Series1.9 engine.Will start and run for about 15 min.Once motor is warmed up good,it will shut off and won't start again untill motor cool s down.If I crank the motor while it is st

Engine Management system (the brain)is overheating which won't register on diagnostics because they just test the systems operating vehicle as to be left running could also be a sensor fault.. Hope this some help good luck

Do you have normal fuel pressure at the injectors ?

You have a bad sensor.

The cold start valve needs to be replaced. It is not letting the engine warm up properly.

Try getting your transmission solenoid replaced. After I got mine replaced it ran fine after that. That's the exact same thing my Lumina was doing.

If it is an automatic shift you should have a neutral safety switch between the key switch and the starter. I would check that and for power at the starter when it fails to crank.
If it is a manual shift there is a switch on the clutch pedal or linkage.
It may be tough to find until you can duplicate the problem on demand.
Could also be a dead spot in the starter or solenoid.

I don't think there is a heat shield on the starter but, I wouldn't think that would be you're problem. I would try changing the ignition module. It's on the engine block, drivers side, I think. Usually when they are going bad they will shut off engine when they get hot. It won't crank until it cools off. After it cools engine will crank and run good until it gets hot again. Good Luck.

Sounds like the crankshaft position sensor needs to be replaced. They are a common problem with the Mercedes. That sensor is the one that the engine control module looks at to see if the engine is running. When they get hot and stop producing a signal the engine control module thinks the engine is not running and shuts of the fuel. After waiting awhile they cool down and the vehicle will start up again. I've changed many of them when I worked at the dealer. Tricky part is when there working and the car is running there will be no check engine light on or code stored. Usually will only have the code when the car won't start. Let me know what you end up finding out on it but that would be the first place to look and probably the cheapest.

Wouldn't think sensor or computer problem , more likely an ignition module . When it dies pull a plug wire an check for spark ,i think you will find no spark . Just from my 30 years of diagnosing GM vehicle's this has been the #1 cause of a start an run till warm an dies an wait 20 min . to an hour an it starts again problem. But without testing to know for sure that would be a guess . Having a qualified an certified repair technician diagnose the problem is always the best idea.

your ignition coil are going bad, they need to be replaced. once the car gets hot the circuit shut down the car when hot. once they cool your riding again until they get hot. thats your problem. Good Luck