I have a problem with my Grand Prix GTP. When I am driving it will some times just quit running. It doesn't shake it the motor just goes dead. Use to I could restart it and it would be fine but now I haft to pull of the side of the road and it will eventually restart. I googled this problem and found one man had a similar problem with his Buick and he replaced the crank sensor and he never had another problem out of it. I told this to my mechanic and he said no it would kick out a crank code. The check engine light never has come on and when he hooked it up to a scope no codes came up. I don't feel comfortable driving it very far. Any help you can give me would be greatly appreciated. The fuel pump was replaced a year ago.

Crank Position sensors throw a code if they lose one signal and not the other (3x and 16x). If the sensor completely fails, the computer assumes a stall, with no other point of reference that the engine is still turning. Fueling and spark are cut immediately too, so the engine pretty much drops dead when it happens too. No codes thrown because there is no perceived issue, again, just an unexplained engine stall.

What you can do is check to see if the injectors are firing and spark is happening when the issue arises. An ICM failure can also cause similar issues too.

Sometimes, you can hit the Crank sensor with water to cool it down, and if it was the issue, the car would start.

The proper way to check would be to look at the Crank sensor signal when the issue is occurring, but given the nature of the issue, sounds like it may be hard to catch when it'* a problem.