last week, i was driving at the speed of 65mph in a highway and suddenly i felt that my car was slowing down.
then i realized my engine already shut down. then i was not able to move power steering and guess what i couldn't apply my brake as well. Luckily, due to less traffic, I could took the exit and I was able to rammed my car into the heap of snow to prevent any hazardous consequences.

Then the car start again.

Next day again the car stop while it was running. Then the same problem occurred multiple times.

I took it to Firestone and asked to diagnosis.

According to them, they checked
1. fuel pump, fuse, plug
2. if radiator is charging battery or not
3. anti-theft security checking system.

still they couldn't figure it out.

So, they suggested me to take it to GM dealer.

The car does start now but not sure if it will stop again while running or not.

Any suggestion regarding this.
My car is pontiac grand prix 2007, mileage is almost 100K

What engine does the Grand Prix have in it. It might be a crank sensor. sometimes they act up when they get hot.

no idea about the engine.
car is Pontiac grand Prix 2007
i think engine size is v6

so does the ign control module, but most times they are older how many miles? you can start the engine and heat up the area under the coils and see if it quits, if so it needs a icm. the crank sensor is not easy to reach. it could also be a loose connection on a relay for pcm if you hit a bump or something before it quits

the mechanics from Firestone suggested to take it to GM dealer and according to him PCM or fuse box might be the problem.
Well! today the car did started and run well and didn't stop.
I am planning to take it to GM dealer the day after tomorrow.

Reazon, I know how frustrating these type of intermittent problems can be.
Good luck, I really hope the dealer can find the culprit for you!
GM will scan the car well, test drive, and hopefully something identifies itself.
Oh and I wanted welcome You to GMForum as well.
Please post back what happens after the dealer visit!

Due to the business I am not able to take my car for inspection to GM Dealer yet though it is one of the tasks in my bucket list.
So far, the car is working fine. It'* been like 2 weeks the problem has not been repeated.
I wonder if using the original/master key resolved the problem? I used the original/master key these days as I read somewhere in the post in Google that sometimes not using the original/master key activates the anti-theft lock security system for security purpose. Thus the car would stop.
However, I have been using the duplicate key of a car since last 3 years and such problem never occurred.

Security is not suppose to shut the engine off. Only flash the security light on and that'* it. It'* only designed to prevent starting of the engine.

I think you may have another issue somewhere else.

What you should do is go to a place like AutoZone, and have them scan the vehicle for free.....if there are no codes(could be a history code if the CE light is not on), and it'* been 2 weeks since the last "concern"(I just love that GM term), chances are taking it to a GM shop could be fruitless, unless you get a savvy tech, who has run into this problem before, and knows the "usual" spots to check.....

I remember a wire harness problem that was a rub through condition, caused by the A/C accumulator......depending on which wire was affected in the harness, it could cause a plethora of problems....

So just don't be surprised if you go to a GM shop, and they can't find the problem....intermittents are one of the hardest problems to diagnose....

It'* been almost a month, the problem that occurred last month has not repeated again.
my ponitac grand prix 2007 is running well.
This coming weekend I am planning to take my car to autozone for scanning.

I have a hunch that it may be the ignition switch problem (GM faulty Igniton recall ) that I can see all over in the news.

Let me recall the incident.

Last month I was driving at 60-65 m/hr. Suddenly I noticed that the speed of the car was decreasing. I tried to
swift the car to the complete right to pull over, then I realized the stering was locked. I couldn't move it. I tried to press the brake but I couldn't apply the brake.
I felt like someone had put something to block the brake. I couldn't press it at all. It was jammed.
I panicked, and then I switched from Drive mode to Parking mode assuming the car would slowly come to stop. (I should have switched it to neutral and then applied the hand brake
but i panicked as steering was jammed, so did the brake)
Further to decrease the speed and to prevent being hit by any vehicle on highway, I took the exit to small road that had a bit upward slope.
As the exit road had a bit upward slope, the speed was decreased. To prevent any accident hitting the pole or any other vehicle, I rammed the car into the heap of snow and finally it stopped.

After pulling the car out from the snow with the road assistance, I drove to my work. In the evening as well I drove 35 minutes on the highway back to home. It had no problem.
However, next day when I was taking the car to the workshop(firestone), on the way it stopped at least 3 times.
The firestone people said, next morning when they tried to start the car to diagnose, the car didn't start but however, later in the afternoon it did.
since then the car did always start and is working fine now.