I drive a 99 XJ 4 speed auto and just today I had a pretty confusing issue.

Ran fine this morning and then leaving to go into town in the evening I had a small ABS event, where my brakes lock and won’t release (pedal doesn’t stiffen, stays the same as normal) I figured no big issue, maybe mud on the rotors since I live on a dirt road, just cut the engine and restarted it and it was fine. I made it into town (about 12 miles from home) and I had a very intense ABS event in a parking lot. Feels like every single brake locked and it won’t roll in drive or reverse until I hit about 3000 RPM and it goes to a crawl. Checked my fluid, still good, reset battery, no luck, removed and replaced fuses and still no luck whatsoever. When the ABS light kicks on and stays on for more than 10 seconds it wayyyy overpowers my battery and my amperage goes pass the max on the dashboard.

I’m not unfamiliar with jeeps or working on cars in general and I can’t narrow down what the issue could be and that scares me.

If anyone who’s ever experienced something close to this give me some guidance you’d be a lifesaver. I just hate being in a pickle like this and not being able to get a definitive list of answers. PLEASE HELP

 

Have you tried driving it without the fuses? When you say amperage, do you mean voltage?

 

no because I wasn’t sure about the fuse that controls the ABS underneath the glove box due to it controlling solenoids and a bunch of things inside the cab of the Jeep. Didn’t want to run the risk of damaging anything else. And the fuse under the hood says it’s only for the light so I figured that wouldn’t help much of anything

and yes I meant voltage my apologies on that part.

 

Next best option. Pull the plug on the ABS unit.

 

might be my next best option because she’s stranded in a parking lot as of right now and that’s never a comforting thing. I appreciate the suggestion!

probably gonna want to pull the ABS system altogether on the damn thing. My TJ didn’t have ABS and I survived pretty fine

 

It sounds like the computer is recieving the wrong signals from the Wheel Speed Sensors (WSS) for some reason. If the speed being sensed at the individual wheels is recieved as being different from the other wheels (mainly the two wheels between the two axles..) the ABS may be engaging since it thinks the wheels have slipped or lost traction from each other. There are a few different things that come into play for the WSS. Such as the power of the magnets or their condition messing with the Electromagnetic Field, the reluctor ring condition at the wheel, the gap between the sensor and the reluctor rings specific teeth, the wheel speed, etc... It could also be something on the computer side like the ABS Module itself being faulty. Or, a connection/wire to and from the ABS Module to the main vehicle computer. Or, a wire/connection from the module to one of the WSS.

If all four of the wheels are all locking up like that. It very well may be the ABS module because I doubt all 4 WSS and their associated components have a fault like that all at once. Although, it could maybe be on the circuitry or wiring with an intermittent short or something to cause an overall effect on the entire system too?

It sounds very much like a faulty ABS Module to me.

 

as stated above unplug it and see what happens, I agree with Noah911, the chances of all wheel sensors going bad at once is a long shot. I'm perfectly fine with no abs, my drive way is 300ft up a steep hill in central pa and never needed it...then again i grew up with vehicles with out it

 

THANK YOU EVERYONE FOR THE HELP

as an update:
removed the main ABS fuse and tried to run it without and I’m not sure how it happened but it send the whole truck on the fritz, my entire cluster except for the RPM and speedometer went completely dead for about two minutes.

it ran noticeably worse without the fuse in as well, sounded and felt very weak driving the less than a mile to the Belle tire

willing to bet that the ABS module went, overcharged the battery due to it being shot and probably fried my PCM because of the electrical overload.

Dropped it off there and waiting for a scan to be run. But as I said above it’s probably both computers which isn’t exciting at all.

THANK YOU AGAIN AND I WILL KEEP EVERYONE UPDATED

 

I do not think the PCM (main computer) got fried. The PCM is very resilient. Even if circuits of the PCM were to get fried shorting themselves out or melting internal components.. even then, so long as whatever got damaged was not critically needed for running the Jeep, it is still possible to remain having a nearly perfect running Jeep. I would not say something like that would always happen in this way. This is how resilient they are though.

There are a lot of different safe-keeps and stop-gates set up to protect the PCM all over and throughout the Jeep, and inside of the PCM as well.

I would not think a fault of the WSS's, ABS Module, or any of the associated parts would really have a devastating affect on the PCM itself. It could have an external effect on it though.

What I would worry about now of the problems you are having with the way your Jeep is behaving with the ABS fuse removed.. if the issues do not go away? Maybe the ABS module is really actually okay? It could be maybe there was a shared problem happening externally to it along with some of the other closely associated components to the ABS Module? By removing the ABS Module, it could have sent the majority of whatever the problems influence was to the other different circuit(s), instead of having the ABS system taking the brunt of the effect from whatever the primary fault actually may have been.. maybe? This would be how I would think of it. If this were the case? I think looking at electrical diagrams for your Jeep would lead to whatever areas may need further investigating at in order to find and fix whatever the reason may be..

I do not think pulling the ABS fuse should have caused a bad effect like that to your Jeep. Maybe try resetting the computer with the PCM reset procedure..

 

Now that I think of it. You did say your voltage gauge drastically dropped voltage when the episode was happening. This is a pretty good indicator that there may be a rather large electrical problem occuring somewhere to effect the voltage like that...

Keep us updated.

 

alright guys! We got it figured out for the most part, and it was the strangest thing that caused the issue and took me almost all of the day along with the fantastic staff at the Belle Tire in Lapeer MI.

So the very base of the issue and what had caused it was my serpentine belt that was slipping just a bit but due to a wild temperature change in my region of MI or some other unknown factor, the belt had gotten much more loose and was practically slipping off of the pulleys. (Never had this issue ever before and have owned it almost a year) This solves the very rough idle and running issue when I had pulled the fuse this morning to try and remove ABS function.

So since my belt had slipped so drastically it has sent most of my electrical on the fritz and had (in my best guess) freaked out the ABS module causing it to demand so much electricity that it had begun to overcharge my battery.

by extension of that it destroyed my alternator and it was barely functional when we pulled it at the shop

the electrical had overloaded my PCM, not my ABS module and we know that from the codes we have pulled post solving the problem. To further support this the overcharging has confused the transmission so much to the point where putting it in plain old DRIVE and not selecting a specific gear would push it all the way to fourth gear; which explains the feeling like my brakes locked when in fact they didn’t, my transmission was shifting well out of turn due to the overcharging of the PCM.

So from that electrical overload it has sent my error code system on a rollercoaster, when they ran the scan in the morning upon arrival I had close to 20 error codes come up.

we had reset and tightened the belt and that solved almost ALL of the issues. Now there’s still the damage that was done to the PCM from this silly and unpredictable issue and now my cherokee is only pulling three codes after replacing the belt and alternator.

the first is “Abs 37-system over voltage” which means there’s still a reason for there being a little too much electricity being pulled towards the ABS system

the second which is the last piece to the puzzle is “P0622-generator field not switching properly” which is either caused by faulty Alternator pulling more power than what the PCM or ABS module asked for, or a damaged PCM and since the old girl has a new alternator it leaves only that issue.

the third code is an O2 sensor but that’s because I don’t have a Cat on the exhaust so that’s ultimately unimportant.

so I plan on ordering a plug and play PCM for my cherokee so I can rid myself of this ABS overcharge issue being a risk in the future.

by 5:00, when belle tire closed I was on my way home and made the whole 12 miles (which is 55 mph most of the way and country dirt roads for the last 4 miles) without my ABS kicking on, my trans shifting out of turn, brakes locking or any issue like that. I’m very fortunate to not have my PCM be totally shot but it needs replacing very soon before I take it anywhere far.

again shout out to you guys for ideas and pointers and huge thank you to Belle Tire in Lapeer, especially manager Rob Stitt and their mechanic Mike for helping me out LARGE and not taking advantage of a young guy who was in a jam. They had allowed me in the garage and be extremely hands on with all work and testing they did so we could come to a very promising solution to one hell of a mystery of an issue.

if I leave any missing links in this mystery just ask, so much has happened today with that I can barely think straight. Thank you guys again. Really starting to love the XJ community a whole lot more than the TJ guys I’ve dealt with.

 

Wow! That is kind of amazing and very unusual thing. That is great you got awesome service at the shop for this issue.

The code you still have present is a dangerous code. Did they warn you about this? The present P0622 code is not an issue for any intermediate mechanic. A professionally certified ASE (National Institute for Automotive Service Excellence) mechanic is recommended for diagnosing and repairing issues like this. With no professional experience and only limited knowledge.. I would steer clear of even attempting suggestions to someone on how to further diagnosis, test, or fix this one.

This code is for the field circuit of the alternator/generator. I have actually worked very closely with a good personal friend of mine who is also an ASE certified mechanic of many years. Him and I have messed with fielding an alternator together before. I remember him warning me about this code when we were working on a vehicle this one time. It is one thing to do diagnostic tests on a vehicles field terminals. So long as you take the appropriate added precautions ahead of time and set a time limit. It is a totally different thing to attempt fixing a vehicle actually having a problem with an alternators fielding as its baseline issue with a code such as this one.

I highly recommend having only an ASE mechanic find and fix this issue if a new PCM does not resolve the problem code! Nowadays nearly one hundred percent of vehicles presenting this code it is the result of having a faulty PCM. It does not have to be the PCM having the fault though.. And with how the issues came about for you with your Jeep it sounds as though there is a distinct possibility of having one of the other reasons outside of it being a fault with the PCM. If it is not the PCM when you swap in a new one? I say take it to a reputable mechanic at that point.

Let me just give you one example of why I say this. If there is a blown fusible link causing the miscommunication of pulse width modulation with/to/from the PCM and alternator, and you were to find and repair a bad fusible link without first finding any and all of the possible shorts which caused the fusible link to go bad in the first place. Well, very bad things can happen if you were to think it was fixed.. and you were to run your Jeep like that for a length of time like that... A full-field short, or a berserk regulator running for awhile will cause major overheating of the battery, including an explosive mixture of major amounts of hydrogen and oxygen! It would only take the smallest of electrical spark to literally blow your Jeep up with you inside of it!!!

If you are going to be driving your Jeep any before fixing this code? I would watch the gauge for your battery voltage like a hawk with binoculars if I were you. Maybe, think about parking the Jeep until you get the chance to swap in the new PCM.

 

I didn’t realize that code was such a serious issue, the mechanic had just said that it’s common when PCM’s go on older jeeps for that code to pull up and that he was “certain” a PCM would fix the problem but man you certainly paint a scarier picture putting that code into perspective. I had googled it and thought the PCM was the simple fix and I hope that it is.

And yes I don’t plan on taking it anywhere until I replace that PCM because I was worried about further issues due to that code coming up.

Also I run an Optima red top in my XJ for the high cold cranks and the near impossibility of acid leaking anywhere. Does that possibly increase or decrease the risk of something catastrophic happening?

definitely looking into this more in the AM and once again I appreciate the help and guidance on that issue as well. Once again will keep you guys updated on any issues or solutions that come up!

 

I would also like to note that with the resetting and tightening of the serpentine belt that any running issues the Jeep had disappeared minus the engine code coming up which hopefully can mean it’s just the PCM.

looking up symptoms of that unnerving error code I’m not seeing any that were there before the whole ABS incident and none of those issues are there afterwards either. Even with the issues it had running for the super brief period of time it still had no problem turning over.

so bottom line is that I’m cautiously optimistic that it’s the PCM. But we’ll see soon enough, probably within the week accounting for shipping time.

 

I read something about it last night before I posted my last message. I know a little about all of the different computers (ECUs) on these Jeeps, and for vehicles in general. What I read makes sense to me with what I know.

It was saying there is a dedicated primary ECU (a non-PCM ECU) to also throw a code for in these situations. There is also a backup ECU to throw a code for the first primary non-PCM ECU.. to throw a code in this situation should the first ECU have been taken out by a high surge of electricity somehow in some way... There is a chain reaction of events.

The different sources all mentioned the ABS Module (this module is just one of many Primary ECUs.. second in command behind the PCM of course). They say in general the ABS Module is ussually on the top of the list as a module to be reporting a problem by throwing a code when there is an issue with alternator fielding and the pulse width modulation communication to the PCM. So, it makes sense why your Jeep had its ABS Module freakout during the episode, and for why it has a code remaining afterwords.

In semi-modern vehicles, the first suspect is always the PCM. This is because the alternator fielding is regulated internally by the PCM. I believe there are ways to test your PCM to see exactly what is happening inside of it right now. I still would not want to mess around and would not recommend attempting any diagnosis or any fix to this other than maybe trying to replace the PCM and see if it goes away. It is not that the regulator pulse width modulation function has failed.. It is a loss of communication on the pathway between the alternator and regulator function of the PCM and the whole PCM interface to it.

I do not understand it all? I have not really looked into trying and understanding it in all honesty. I am not sure what type of back-up plan is in place for in this situation. Maybe there is a set charge rate in play now? The alternators charge rate effects the vehicles fueling, timing, spark, air-intake, and overall engine functions... If certain accessories are on that require more electrical energy such as air conditioners, high beams, the heater, radio amps, a winch, a snow plow, old-school police lights & sirens, etc... The alternator needs to work harder and the different engine functions all need to pick-up to compensate for this.

It is a bit involved all of the circuitry involved on this particular malfunction.

I do not think it matters what type of battery you have when it comes to super-heating the internals. The amplitude of this type of electricity is able to cause major destruction to occur. The by-products are highly explosive. Although, I am not sure what type of worst-case explosion could result? I would not want to find out personally first-hand. If it were to happen while driving... It would not take much to have a fateful outcome. The implications are disastrous.