I posted an earlier post on some of this - My 1994 Cherokee 4.0 automatic still won't start. It was showing Code 17 which is the Coolant Temp Sensor. I replaced it and that Code is gone, but I'm still showing a Code 12 and still not starting. The Haynes says Code 12 is Battery Disconnect to PCM after 50 Key-Ons. What does that mean??? A friend told me that I have turned on the ignition key 50 times without starting the vehicle and it shuts the computer down. Hugh? He said to try turning the key on 50 more times and it might re-set the computer. So I tried it. At about 38 key-ons the dash buzzer came on. So, I thought - what the heck! I tried to start it and it fired right up. It ran rough and smoothed out - BUT(!) after about 45 to 60 seconds it died again and won't start again. I tried 50 key-ons again with no luck. Do I need a new computer or what? I am totally lost. Can I take the computer out and have someone test it???

 

Code 12 means that you lost power to the ecm recently. Usually this is from disconnecting your battery to work on something. If your battery has not been disconnected I would start looking at the condition of your battery terminals and freshen up all of your grounds.

 

Sounds like it maybe in the ignition switch may want to check it

 

Also check to see if your gear selector is all the way in park mine sometimes won't go in all the way and it won't start,

 

On an earlier post about this I mentioned I had changed my fuel pump about a month or two ago........it appears to be dead. I unhooked the hose and no gas comes out at key on or when I crank it over. I just found out that it's all over the net that Airtex fuel pumps are junk. I'll check for power, ground, and the relay first before I throw it thru the window at Autozone!

 

key on and off so many time maybe fuel pump issue ,spray some starter fluid in the air box tube see if it fire its very possible pumps gone...

 

Sounds like the cps, or a ground on the fuel tank I had to ground my tank to the frame rail to get mine running right after I knocked the tank out from under it hitting a rock.

 

^ wheres the fuel pump ground originally located? Pictures please? Im having very random intermittent fuel pump problems.

 

Mine had one off the fuel pump wires to the body, but I also put a ground strap I got off a Ford and clipped it on the lip of the tank to the reciver hitch mine runs great now,