I'm new to this forum, and in the following description, you will find I know nothing about vehicles.

I was driving to Tennessee today. Had no problems starting out. Once the Jeep was required to climb some of the larger hills/mountains, the check engine light came on and began flashing. I drove about another 5 minutes, trying to get to a gas station. Then, the vehicle began to shudder, or as I would describe shake, or miss.

I pulled into the gas station, shut off the engine, let it rest for about 10 minutes, and restarted the engine. The engine light remained on, but did not flash. The car ran normally. I continued my trip to Knoxville, as that is where the closest Jeep Service is located.

When arriving, and having no other problems, I disconnected the battery posts to reset the sensor. The light remained off, and I drove around for about 2 more hours with no other incident. I drove home, and the car behaved fine, until I was required to begin climbing hills/mountains again. Same incident. Shutting the car off again, fixed the problem, and I was able to make it home. The engine light is still on, but it is not blinking. I live about 45 minutes from service, and of course they are all closed for the weekend.

Any clues as to why this is occurring, and resets itself when the car is powered off?

Disconnecting the battery is clearing the computer of it's codes.

Us helpful types here first need to know what year your jeep is so we can tell you how to pull the error codes that made your check engine light go on. DON'T disconnect the battery! You'll lose whatever made the check engine light go on.

Disconnecting the battery is clearing the computer of it's codes.

Us helpful types here first need to know what year your jeep is so we can tell you how to pull the error codes that made your check engine light go on. DON'T disconnect the battery! You'll lose whatever made the check engine light go on.

Sorry. It is a 2003 Grand Cherokee, Larado, V6, 4 door. Approx. 47000 miles

This info comes from Allpar:

For the 1999 Jeep Grand Cherokee and up, you do the switching the key on and off 3 times, but not quickly. You turn it to on so the odometer turns on, turn it off, and then back on, wait for the light to turn on, etc. On the fourth time you'll get a code, or you'll get the word "done."

At this link:

http://www.allpar.com/fix/codes.html

Try that and post whatever codes you get. I expect to see at least P1684.

the light flashes because the engine is misfiring, anytime the pcm considers the misfire to be 1 1/2 times the emission failure the light flashes

there is a tsb 09-003-03 which could help?

there is a tsb 09-003-03 which could help?

I'm new to the forum, and don't know how to find the 09-0003-03 you reference. I did a search, but it came up with 0 results. Can you tell me how to find this tsb you reference. Thanks!

This info comes from Allpar:

For the 1999 Jeep Grand Cherokee and up, you do the switching the key on and off 3 times, but not quickly. You turn it to on so the odometer turns on, turn it off, and then back on, wait for the light to turn on, etc. On the fourth time you'll get a code, or you'll get the word "done."

At this link:

http://www.allpar.com/fix/codes.html

Try that and post whatever codes you get. I expect to see at least P1684.

Thanks for the information and the lesson in finding the code. It came up as PO300, which according to the chart, and the service manual we have, indicates a muti cylinder misfire??????????

Actually one too many zero's I think it's 09-003-03 but what I came up with at Alldata wants to sell you the info.

You could go to the parts counter at a dealership and ask, they can find it. The code you have certainly points in this direction.

Thanks for the information and the lesson in finding the code. It came up as PO300, which according to the chart, and the service manual we have, indicates a muti cylinder misfire??????????
That is correct for that code and matches the drivabilty problems you have/were having.

MORE INFO.
Code P0300:
Random/Multiple Cylinder Misfire Detected.
Misfire detected in multiple Cylinders.

Flashing check engine light.
From the factory service manual:
"If the light is flashing, severe catalytic converter damage and power loss will soon occur. Immediate service is required."

Meaning- stop driving ASAP, there is a serious problem, mainly the severe misfire, which could damage emission components of the engine.

Now, what is causing the misfire? Since it seems to be consistent with driving uphill, I can almost guarantee one of two things is happening:
Fuel starvation or overheating.

Overheating-
Have you checked the temperature gauge when the engine starts to run badly?

Fuel starvation-
The possibilities are a bad fuel pump, clogged fuel filter, fuel leak etc. Have your mechanic or friend check it. The fuel pressure should be at 50 psi at all times, +/- 5 lbs.
It could also be a problem with the fuel tank since the fuel moves to the rear of the tank when going uphill, more so when the tank is less than full.

Edit: Another thing occurred to me; what is the elevation of those hills and mountains? The engine has a sensor that keeps the fuel ratio consistent at different altitudes - this could also be a possibility.

Hope this helps.

I have a 1999 Jeep GC and on mine when that happened it was a air temp sensor screws into the intake manifold I believe its been about a year since I replaced it wouldnt always shudder but the (faulty/fried sensor was reading the air temp to be 300*F or more) is about $30 at autozone and took about 20 minutes to change max due to obstuction if i remember correctly