Montana keeps dying

I have a 2000 Pontiac Montana. I have been having this problem for 8 months. The car on occasion , now everytime dies the minute you shut it off. I try to restart it and nothing. I can boost it and it works sometimes . My mechanic is so puzzled. Everytime I take in it works agains. He thinks its a pull from somewhere but cant find it. He has cleaned the battery connections and for the first 3 months of problems it seemed to correct itself.

I have a 2000 Pontiac Montana. I have been having this problem for 8 months. The car on occasion , now everytime dies the minute you shut it off. I try to restart it and nothing. I can boost it and it works sometimes . My mechanic is so puzzled. Everytime I take in it works agains. He thinks its a pull from somewhere but cant find it. He has cleaned the battery connections and for the first 3 months of problems it seemed to correct itself.

Could be a crank position sensor. If your van was built like the 1999, there are two, one on the crank externally behind the main crank shaft pulley, and a secondary one internally.

The external one has been known to case this problem, but often it is during a cold start not necessarily a warm or hot, but this could also happen. When it fails, or works intermittently, the ECM is unable to sense the crank rotation.

Might want to find another mechanic who has the right tools to do an ECM scan looking for a code, and works on these vehicles routinely.

Are you saying it is dead, as in it acts like the battery is dead when you try to start it? If so, see if the headlamps work and A/C blower fan run when the problem happens. Then we can isolate the cranking system from the rest of the electrical system depending on your results.