1999 Pontiac Grand Prix GT randomly cuts off



1999 Pontiac Grand Prix GT randomly cuts off.

Car cuts off randomly at any time while driving 70mph down the highway, at a red light, and sometimes will not even start. The car can behave this way 6x a day or go for a week without cutting off. Sometimes the car cuts off, then starts itself right back up without me trying to turn the key. The car will not cut off for the mechanics. This problem has been going on for two years! There are no error codes in the computer. I have checked many times. No lights on the dashboard turn on that warn of a problem.

Sometimes I can start the car right up and drive away. Other times I have to sit on the side of the road and wait 5-10 minutes to start the car. The starter will crank and crank, but the engine will not turn over.

The problem with the car is dependent on the temperature outside. If the temperature is greater than 70 degrees the car will likely cut off.

It seems to help a lot if I have the heater on. If the car cuts off, I put the heater on and wait a minute, then the car starts up with no problem. Usually, the car would take many cranks to get going without the heater on. Sometimes I just drive with the heater on and the windows down to reduce the chance of the engine cutting off, but in the summer it?s unbearable.

Things I have done:

Replaced a broken thermostat

Swapped out my coils with a 1998 Camaro, but the car cut off, then restarted itself. The original coils are back in the car.

Changed spark plugs

New fuel pump and fuel filter

Add fuel cleaner to the fuel tank

Switched gas stations

Any ideas?

Thanks in advance!



Maybe fuel pump relay. I had a similar problem went away when I replaced the realy.


It could be a defective ignition control module. A defective module will shut down the engine as it heats up, when it cools off the car will run again until it heats up.


Thanks! Was your problem on a Grand Prix, too? Also, did you have any error codes on your computer. My mechanic seems to think that the relay would throw a code.


Thanks! I’ve heard that it might be the ingition module before. The ignition module could very well be the problem.

One challenge I face now is that I’ve spent over $1200 on fixing the problem and no solution has worked. I’m tired of throwing parts at this car and after two years it doesn’t appear that the problem will ever fail consistenly enough for a mechanic to see the problem and diagnose it.

Once, my car was 20 feet away from a railroad crossing when it stalled out. A train wasn’t coming, but the scenario is definitely not a good one. I wonder if it’s worth it to buy a new car or keep buying new parts. What do you think?


I don’t believe you should buy a new car just because you are having problems with this one. It could be a simple fix with the proper diagnostics.

The best way to find the problem is to have someone diagnose the problem while it’s acting up. The basics need to be checked while it’s not running… is there spark and fuel?

Carry a spare spark plug with you and the next time it quits pull a plug wire off and see if there is spark while you crank it over. Be careful these coils carry quite a punch, enough to kill.


Thanks! I guess I’m looking for the absence of a blue spark if the spark plug or wire is defective, right?


If there is no spark that will help in diagnosing the problem. It still could be a number of components causing the no spark condition. Finding out if it has spark or not will give you a place to start from.


Unfortunately it wasn’t on a Grand Prix but a 1990 Dodge, but what you describe matches exactly what I was seeing. The faulty relay never threw any codes on my car, but that was before ODB-II codes. I don’t know if the newer cars through a code for a faulty fuel pump relay or not. If all else fails might be something to keep in mind, might not be terribly expensive. The part was somewhere between $30-$50 on my car and very easy to replace, don’t know if that would hold true for your car though. Good luck.


It is not a good idea to be throwing parts a problem, it will just lead to more frustration and drain your wallet.

If the poster finds that there is no spark then putting in a fump pump relay was just a waste of time and money.


Bad fuel pump relay or fuel pump ready to go. But the condition should throw a code. Could also be ignition control module in which case you would get a code.


Sorry… but you will not get a code for either of these conditions. Try guessing again.


I replaced the fuel pump already, which was a mistake. I think the mechanics got the better of me there. I’ve heard that when a fuel pump dies, it dies. The pump does not linger around for two years. Thanks, though.


When it does not run you need to check for spark. If there is none, then there are only a few typical problems. Ignition module, crank sensor, and cam sensor if there is one. All these components can act up when hot and be fine once cooled down. Ive replaced 4 GM ignition modules before, and one GM crank sensor.


Thanks! You and willey have convinced me that I need to buy a new spark plug this weekend.



Something similar happened to me. I had a 1987 Dodge Aries that would cut off all by itself at random times. It turned out that the system that traps gas vapors from the gas tank was plugged up, specifically the charcoal canister. The fuel pump wasn’t able to overcome the vacumm created in the gas tank as gas was pumped out, and the care would stall.


Interesting. How did you determine what the problem was if the car was stalling out randomly? From what I’ve learned so far, there are a million things that could cause my car’s problem, so trying to find the culprit is difficult since the problem cannot be reproduced on demand.


I have a 1995 Grand Prix GTP that had the same problem. I replaced all kids of sensors, including O2 sensor, Idle Sensor, etc… Finally talked to a mechanic that knew something. Since you have a 1999, I am not sure it will help, but this is what I did. Locate the EGR valve which should be located on the top and back of the motor. Unbolt it, pull it to the side, and look in there. There will most likely be carbon build-up. Take a screwdriver or small scraper, and clean the inside up to where you can see bare metal…bolt it back on and BINGO…problem solved! You may have to do this every 5000 miles or so or you can spend a couple of hundred dollars on a new one…cleaning it will save you money…hope it works…oh, by the way, the computer will not pick up any error messages when it is this problem…Good Luck!


Thanks! I’ll try that as soon as I can find the EGR valve :slight_smile: I’ll let you know how it goes



yep, crossing my fingers for ya! When my GTP ran good, it ran good, but when it screwed up and left me stranded, I was ready to beat it in with a bat! When I cleaned off the EGR valve after the suggestion, it ran like a new car! I sure do miss driving it since I have a Suburban now. Talk about getting nowhere real fast and I cry every time I put gas in it! let me know how it works for ya! oh, by the way, if you can’t find the EGR valve, look on the web and type in EGR VALVE GRAND PRIX to find a picture…later!