Welcome to the wonderful world of jeep. If you own or have owned one of these you understand that this has happened to you before. Well lets get started. The most common things that could happen are dead battery,corrosion terminals,broken wires (from the battery to the starter positive side or the battery to the frame and engine block ground side)bad or shorted starter,crank sensor, cam sensor,unable to read security key,bad fuel pump and to finish this long list the jeeps computer also called the PCM.
I have worked as a jeep tech for seven years and have bin certified by jeep to repair anything you can think of. Their are some things that i did not put in the list because of how uncommon thy are. I had one jeep that refused to start every time and everything on the list was ok and working properly. I found six broken wires in the injector harness. If you cant get you jeep started after a few steps and have little or no automotive experience please take it to a good shop,especially one that deals with electrical problems. If you choose a shop other than the dealer be prepared to be out of you jeep longer due to the simple fact,the dealer fixes jeeps everyday and have bin well trained and more than likely has seen you problem before.
Ok class lets get started first thing is to try and start the jeep. What did you hear? Anything nothing will start here. We'll say you heard nothing turn the key again and make shore. Still nothing look at you instrument cluster is their a symbol of a key? If so stop here their is nothing you can do the security key is not being seen by the computer. Off to the dealer for you. The key need to be reprogrammed or the key sensor is bad in this case the dealer is the only one that do this for you,do to the fact of the equipment used 99 percent of most shops do not own the proper tools.
Ok you turn the key and hear nothing and don't see a key symbol displayed on the instrument cluster. Turn you head lights on and turn the key again. Do they dim? Yes, well time to pop the hood. look at the battery are the terminals clean? No ok go inside and get some baking powder and a cup of water. Sprinkle the baking powder over the top of the battery use as much as you like. Pour the water on the battery slow just to make it moist. Now Waite about 5 to 10 minuets. Now pour the rest of the water on the battery to clean all the baking power off. Now their cleaner go and try to start the jeep now. Still nothing well its time for a jump use your owners manual to find the proper procedure. If this worked please have your alternator tested for it may be weak and undercharging or not charging all to gether.
If you still in counter a no start problem now on to the next step. Time to check the starter, most of the time the starter will make a clunk noise. If you try ed a jump and nothing happened or you herd a clunk noise (will sound very faint from inside the jeep) but the engine does not turn over well its going to be the starter. Please DO NOT HIT THE STARTER first what did it do to you and second it wont help. You have a better chance of do more damage than good. Starter replacement is not that hard any shop should be able to do this for you.
Ok so your jeep turns over (engine spins or rotates) well it takes three things for any car to run. Fuel,air and spark remember air is free so thats not the problem. If it spins over slow you have a battery issue a jump should help you. Now this is where it gets tricky. Fuel is suppled to the fuel injectors by a pump but their are sensors that turn the pump on and off. If you turn you key but not to start for the first time you should be able to hear a low pitched hum that means the fuel pump has primed the fuel system. No hum bad fuel pump. Please note this only happens when you first turn the key on. Their is a technical service bulletin for 99-02 jeep grand cherokee for extended crank time(takes to long to start) it has to do with the fuel pump and replacement of a o-ring in the pump it self. It is cheaper to have the tsb done rather than replacing the expensive fuel pump.
On to spark. Like the fuel pump it is controlled by the computer by sensors. The 2 main senors are cam and crank. The crank sensor tells the computer at which position the engine is at. In order to figure out which injector to fire or which spark plug to ignite. When the crank sensor fails the engine WILL NOT START but will rotate. If your check eng light came on the night before. You need to take it some where and have the jeep scanned. (using a hand held computer to retrieve codes) The codes will tell which part has failed. The check engine light will come on when you turn the key on its called a self check. Do not be alarmed if the light stays on if the jeep is not running it is normal.
The cam sensor is just like the crank sensor. The cam sensor controls spark only. Some of the older jeeps has a distributer,plugs and wires some time a tune up is all thats needed. The newer jeeps have a coil pack design witch relies on the cam sensor for ignite the spark plugs. Jeep had a problem with the newer stile cam sensor (located in the same spot of the distributer in the 6 cylinder engines) it is driven by the cam shaft. The shaft that spins the contact for the sensor would cease up and stop rotating but would also turn the cam sensor. It is easy to see and is very common. It will also set the check eng light.
The last thing on the list is the computer. If the computer does not see the info it needs coming in it does not know what to do. The computer does go bad on its own due to vibrations, moisture and voltage spikes. When the computer goes bad it could do a lot of strange things to nothing new at all. A scanner will be needed to figure this one out and a wire digram this is not for the faint of heart. The one good thing is the computer has a longer warranty than most people know of. By federal lay the computers warranty has to be 8 years or 80000 miles. Good for you bad for them.
I could list more problems but these are the most common. To all jeep owners and will be owners jeep is a good product just like any other car out their they all brake down. Sometimes its more expensive then others but i have personally seen jeeps that have 400000 miles on them and still running. Every car has problems just get what you like and what will make you happy and fit your needs. In the end your the one stuck driving it.