Vehicle is a 94 Grand Cherokee Laredo. 5.2 engine, auto trans, air conditioning. 99,000 miles.

Problem(s):

1) Engine light would come on after about an hour of driving. The idle was slightly erratic at times. as well, but usually idled fairly smooth. Checked the codes and 25 came up. Idle Air Control. I unplugged it and re-plugged it in and it seemed to fix the problem. It now idles smoothly.

2) Code 12 also comes up. This has me stumped. How do I find the cause of this problem?

3) Code 33 comes up. Air Conditioning. I checked the fuses and the relay. All good. Pressure in the system is 45 psi. The clutch does not engage. I jumped the wires on the pressure switch on the dryer tank and THEN the pump engaged. I let it run for about 5 minutes and rechecked the pressure. Still at 45 psi, but no cold air coming out of the vents. The small aluminum tube that goes into the firewall was cold though, but no cold from the vents. I plugged the pressure switch back in and the clutch dis-engaged. I unplugged it and put the jumper back in and the clutch engaged. Can I assume that the pressure switch is bad? How do I change it? I can see that it unscrews, but will that release the freon or is there a check valve of some kind under the switch?

Here is the story:
Bought the Jeep about a month ago. Ran fine, no problems at all, but just short trips to town. The first time we went on a longer ride, the engine light came on after about an hour of driving. vehicle still ran good. If we shut the engine off and restarted it, it would go about an hour and then the light would come on again.
When we got home I checked the codes. 12,14,33,55. I checked the Map sensor (code14) and it checked out good. Then I got busy with other things and never checked further. Never went on long trips either so the light never came on.
Recently it started idling rough and erratic. Checked the codes again. Now I got 12,25,33,55. I unplugged the IAC (code 25) to make sure the connector was clean and plugged it back in. I also sprayed carb/choke cleaner into the throttle body while it was running. Took it for a drive and it ran great, idled good as well. Decided to go for a drive today to the closest auto store that had an IAC in stock, which is about an hour drive. Drove it about an hour and a half and no engine light came on, so I figured the problem was solved.
On the way home, after about 20 minutes of driving, the light comes on again! Checked the codes and get 12,32,33,55. Now, some of the trouble codes show 32 as being an EGR issue, but I can find no EGR valve on this vehicle? I see on the Auto Zone website that they sell one for this Jeep, but I don't see it on the vehicle? Most code charts that I have seen go from code 27 right to code 33, and yet I do get a code 32 from this Jeep.

Can the code 12 problem cause me to have false readings as far as the code 25, 32 goes? Code 33 is explained above, and I know that 55 means the reading in complete.

So I guess I'm asking (after a lot of rambling) how do I go about finding the reason for code 12? And, can the code 12 be responsible for the other codes (minus 33) coming up?

Thanks in advance for your patience in reading this and for any info I get.

 

Hello. I had a similar problem with my 94 Cherokee. Various seemingly unrelated sensor and electrical problems. I fought with it for years and changed every sensor on there, some multiple times trying to cure it. Nothing helped. To make a 3 year long story short, it seems all the sensors involved had a blue/black ground wire and they all went into the front that long black plastic strip which runs along the valve cover but only one blue/black wire came out the back. Meaning that inside that thing all those various ground wires combined into one. I took the plastic cover off and found the clump where all those wires joined and messed with it and my problem disappeared! Appearently something in there was either touching when it wasnt suppose to, or wasnt touching when it was suppose to. As near as I can figure all those sensors lacked a good ground because of this and when they would come on (Say after a long drive) they would search for a ground source and not finding the REAL ground they would use another sensor as their ground point and thus cause THAT sensor to read as faulty to the computer! I`m not saying this is your problem but it`s something to consider if you find a number of these items share a common ground point along their path.

 

Your '94 ZJ w/the 5.2L V8 does have EGR. It's located on the top rear pass. side of the intake manifold, between the pass. side head and the oil sending unit, which is next to the distributor.
Code 12 is Power to PCM recently lost. Check the battery cables, and their condition, and the connector to the PCM for any loose wires or pins, or corrosion.
And Welcome to CF!
Dan

 

Code 32 is: "An open or shorted condition detected in the EGR solenoid circuit. Possible air/fuel ratio imbalance not detected during diagnosis".
Code 33 is : "An open or shorted condition detected in the air conditioning clutch relay circuit".
Dan

 

I checked the wiring out and found where the single ground came out of the wiring and hooked up under the alternator. The bolt that held it on wasn't quite as tight as it should have been and the ground didn't look like it was making such good contact. I cleaned it up and put some anti seize on it and then tightened it up good. So far no more problems and it runs like a champ.

In regards to the air conditioning. My info was that 45 lbs was the max a system should have. Someone suggested that the pressure switch needs at least 50 pounds to work. I added some more freon to the system and it works great now. So far.

Thanks again to all who take the time to read these and more so to those who take the time and effort to respond.

 

It's good that you got it straightened out, and thanks for posting an update.

 

Your AC wont turn on if the freon level is too low, saves it from burning up, same as if you have too much in it or there is a clog, when your clutch is engaged and AC is on, your low pressure side should be 40 when running at say 2000 rpm, AC is a pain because it takes awhile for the freon to settle into the system, I usually take 20-30 minutes to ensure proper fill, the pressure at idle depending on outside temp may go as high as 50 pounds,, I never check high side, as it is under High pressure and if your system is working properly there is no need, as you rev your engine you will see the low side pressure go down, you may still be shy of freon.,