My sons 2003 Grand Cherokee has been having weird issues for several months. It started with the gauges pegging out then dropping down to zero while was driving. The vehicle was running fine but the gauges were completely erratic. About 2 months ago the vehicle started having new issues. The vehicle would not start. Sometimes the vehicle gauges would be jumping around with the key out of the ignition. When this was happening the vehicle would not start or would start and immediately shut down. I have not seen this issue myself, only video that my son sent to me. Other times the vehicle would be absolutely dead. There is NO power when the key is in the ignition, no lights, no buzzer, no gauges, nothing. My son would wait and the vehicle would eventually come back to life and start.

About 1 month ago, the vehicle would not start and wouldn't come back to life. There was no power and the vehicle was completely dead like the battery was disconnected. I had my son remove the cables from the battery and short them together to reset the computer. This fixed the issue and the vehicle started right away. My son has been doing this for the last month and the vehicle would run for days without issue then it would act up. During this time the computer may have to be reset 2-3 times for the vehicle to come back to life.

On Saturday, we spent several hours pulling the ECM, TCM, checking connections and cleaning grounding points in the engine compartment. The vehicle has been running fine for the last few days, but I am almost certain that it isn't fixed because I didn't see anything that appeared to be the root cause. The grounds weren't corroded. I did find that when the vehicle had an anti-freeze leak that the TCM had some antifreeze in the connection, but as far as I know it has not had any transmission issues. Used contact cleaner with lubricant to clean the board and the connector before reinstalling.

Things that were observed:
1. When the cables are reinstalled on the battery Hot then Ground. If the ground doesn't spark then the vehicle still has no power and won't start.
a. Not a huge finding but the point here is the vehicle is completely dead.
2. When the vehicle starts it runs without issue and usually for days before it acts up again.
3. My son has noted that he is getting worse gas mileage than before, but he cut the exhaust the 2nd cat and he enjoys hearing the exhaust as he accelerates, so I am not sure he is getting worse gas mileage or he using more gas because he is constantly accelerating hard.
4. Not sure if resetting the computer is fixing the issue or if this is doing something else. I just don't know what else could cause the vehicle to lose all power like this.
5. ECM was not corroded and seemed in good condition. I sprayed the connections with contact cleaner before reinstalling.
6. Also tried moving the shifter through the gears and trying to start. But since there is NO power this was merely eliminating the NSS (neutral safety switch)

I am looking for feedback and suggestions. I am leaning towards buying a reworked ECM but wanted to reach out to others to see if someone else has seen this before and what else I might check before changing out the ECM. If someone has a diagram of the grounding points I would appreciate if you could send this to me. There is one block ground under the vehicle that I couldn't get loose because the vehicle needs to be jacked up to allow the suspension to drop in order to get to this bolt.

Thank You

 

Pretty profound. You say you can't understand that you seem to not get power to the vehicle when putting the battery in, then you jump to something about replacing the ECM.

 

No, when the battery cables are hooked back up if there is no spark then the vehicle has no draw and there is no power (lights, buzzers, ignition, etc). What I was trying to say is that whatever is causing the issue completely shuts down the entire electrical system. Since the only fix so far is to remove the cables from the battery and ground them together to reset the ECM, I am leaning towards the ECM being defective.

But I am looking for feedback from someone that might have any ideas about any other devices in the system that could be causing this issue before I replace the ECM.

 

This sounds like bad cables to me. They can be badly corroded inside the jacket. Since you have cleaned your grounds, I'd start there. Certainly long before I'd replace the ECM. It's possible that's the culprit, but cables are a lot cheaper to replace, and probably need it anyway.

There's someone on this forum who makes cable replacements for the XJ. I dunno about the WJ. I've ordered about 5 sets of cables (different vehicles) from www.bestboatwire.com, and I have been very pleased with the quality and the service. I go up one gauge size from stock, and get the clear heat shrink on the ends. Easier to keep an eye on things that way.

 

X2. Jumping from battery to pcm is a big leap. By the way, when you say you hook the battery up and there is no spark, what spark are you talking about?

 

I'm with these guys.. If the battery terminals are no good, what you described happening is the exact behavior you could possibly experience.

I just replaced the terminals on my 04 WJ for the same reasons. I used mine to jump another persons vehicle one day. Immediately afterwards, I developed a no crank no start completely dead Jeep. My terminals were on pretty good, but not exactly tight enough. I was able to move them around on their posts with a little force. They were stretched to their limit. The bolt was already down tight as far as it would allow. By moving the positive around to where it felt most snug, I was able to get my Jeep sarted.

So, knowing the problem and all.. I still delayed doing the proper fix putting new terminals on for a week or two. Then, one day it wouldn't start again same problem. It would have power inside and all, until I turned the key and then straight dead... I tried snugging the terminals again this time with the parking lights on to see when I got myself a good connection. Went to turn the key, and it did the same thing.. went totally dead on me. I couldn't get it going. Everything went dead each time I would turn the key. I repeated the procedure trying to get better contact at the terminals. Even had headlights with brights on.. full power, but went all dead each time when I would attempt to start with turning the key. I was in a parking lot and heard about the Coca-Cola trick before from someone. I went into the store and bought a can of Cola to poor over and onto the terminals/posts. It worked, and started right up for me!

Thats when I decided it was time to go to the auto parts store, and picked up some new terminals. I cut the wires that went to each of the old terminal ends and removed the factory installed terminals from their wires. Installed the new ones, and the problem is completely gone. It's been good now for about a month...

Edited to add: The gauges went wonky too! They did what you said; went all pegged needles going back n forth etc... when it was acting up with this issue.

I think its probably just the terminals? Probably not the wires themselves... Thats based solely on my experience though, and should realize it could very well be the battery wires, terminals, or maybe both? I know with my condition how I described it above, the terminals did not look at all corroded or compromised in any way (outside of the positive not being on super tight.. bc they were actually quite tight, except for when a good amount of force was applied, I could rotate them around some on the battery posts). My battery is close to new. I got it less than half a year ago. The battery posts are fine.

 

New terminals:
New cables: Bestboatwire.com Go up one gauge size from stock if you want an upgrade. More than that is just a waste of copper. I get them with the clear heat shrink. Makes it easy to spot any corrosion that might be getting started.

 

The wire you have to look at is the smaller of the 2 coming from the battery terminal and goes to the Power Distribution Center. (Fuse/relay box under the hood) That wire supplies everything but the starter cranking supply. Mine was corroded inside the lead terminal. A pair of bolt-on replacements have lasted 5 years now.

 

It has been two weeks since I cleaned everything and it is still running without issue. One thing that I did and forgot to mention was I cleaned battery terminals and cable terminals. The difference that I see with this problem and yours is that when it acts up there is no power. When the door is opened there are no lights, no buzzer, no headlights, its as if the battery is not hooked up. From reading your post it seems that when you turned the key and the system was under a load it failed and everything dropped out.

I did notice that the cable terminal do seem to be wearing from my son removing and reinstalling them to fix the issue. When it was acting up a few weeks ago, I tried moving the cables and the connections on the battery but that had no affect.

I will continue to monitor and post what happens.

 

When the battery cables are installed on a working vehicle there are components that are always pulling power from the battery. So when the cables are installed there is small spark between the battery and the cable. This vehicle doesnt have this spark when it is acting up.

 

I turned the key and shut it off after having just gave someone a jumpstart. A little time later, I went to start it again and it was all dead with nothing no lights or buzzer or gauges. I fiddled with the cables and the terminals once, and it started for me. I had no issues afterwards for a week or two. Then, it was the same thing with it being completely dead when I went to start it again one day after having had shut it down normally. I worked the terminals around to try and get it going like it did before, except this time it would only regain power having lights and door ajar buzzer sound, but it would drop the load going all dead repeatedly whenever I went to turn the key to crank it... It only kept its load and started up for me after I poured a can of CocaCola directly onto the terminals. I thought I was going to be stuck, but that trick really worked to get me going again! Next thing I did was drove straight away to the store, and I changed out the old terminals for new ones. That was the end of it for me, and its now been good for approximately the past two months.

One thing I noted was that when I was attempting to crank it, the positive terminal end would arc & spark as I turned the key to start it a few times, and it would either go all dead-dead, or other times the gauges needles would go crazy. Either pegged or other times going back n forth (that was with the key turned off or on too). I honestly worried that I maybe already had, or was going to fry something!

 

Both conditions are typical of bad connections.