2002 Grand Cherokee Limited, 4.7L no mods. This jeep died after hitting a bump in the road about 1 year ago, yes 1 year ago. It has been in the shop ever since. Had a rollback take to my regular mechanic and it started when the rollback dumped it. It ran for a couple of days afterwards, and that was it. Now the dash gauges are dead, the engine cranks over but will not start, and OBDII cannot communicate with the ecm.
Next had it towed to the dealership from the previous shop. The dealer said they reflashed the ecm and nothing has changed, still no communication, No dash gauges, still will not run. About 4 days before it was towed to the dealer, the head lights came on, the wipers came on, and the horn started blowing, had to unhook the battery before this would stop. The dealer is stumped and on the phone daily with Chrysler trying to see what to check next. This thing is driving me crazy!!!

 

Welcome to CF!

Unfortunately if the dealer is stumped, there's not much I can offer. Maybe it's possessed by demons? It must have taken quite a hit to not function anymore. I'm surprised the airbags didn't pop. There's an inertia switch under the back seat that controls the airbags. I was replacing the rear ABS sensors and my mechanic told me to pull the plug on the switch before doing ANYTHING around it.

 

Sounds like a inertia switch to me,Its ment to cut the fuel if your in a wreck or roll over but if you hit a bump in the road hard enough you can set it off.

 

it only hit a manhole cover in the road, probably amounts to no more than a 1 1/2 inch indention in the asphalt. Surely as many Grand Cherokees as there is out there something similar has happened before. I;m just trying to avoid a 5 or $600.00 diagnostic bill.

 

If it's any consolation to you, I hit a REALLY bad railroad crossing at 40 mph, not knowing it was nasty and I thought my front end was toast, but it kept running and after checking the alignment and looking for broken parts, it was fine. I can't see how hitting a sunken manhole cover could have screwed up your jeep so bad, but you said something about the tow guy dumping it off the flatbed. How bad was that hit? I can't see how you got so many problems unless the motor mounts are bad and the engine thrashing around stretched or pinched a wire harness or something. Usually the first things to go when that happens is the radiator hoses or hose necks start leaking, PLUS with today's type mounts, it can't move that much.

Unfortunately, I think the dealer's DRB III scan tool is the only way to find it, but you also said they've been working on it, right?

 

manhole not hit hard, nothing leaking, off rollback with cable winch, I own 6 chrysler products and can tell you their wiring leaves a lot to be desired. Order ecm today......

 

Yeah....well....Older GM cars were the last time I understood the wiring. The craziest one was my friends 70 Datsun 240Z. In order to save wiring, they hotwired everything and the control switches formed the grounds! Get in a accident and it goes up in flames or everything turns on.

 

The inertia switch has a reset button on it and cost nothing to push it.And i would pray its that vs something else thats gonna cost you deeply.

 

This is on Ford vehicles. I've never seen one on a jeep. The inertia switch mentioned earlier by Dave was referencing the Airbags. Also this would not have killed off all the other electrical or triggered the weird electrical spasm that it had.(And i'm sure the dealer would have checked this assuming this was the case.)

If the dealer was able to communicate and re-flash the ECM it's internals must be ok. I'm suspecting it's something stupid like a broken wire in an innocuous spot.The fact that it started after getting off the tow truck lends more credence to this, as the jostling of being on loaded, transported, and unloaded may have been enough to temporarily close the broken circuit. Could also be something like a broken solder point in one of the modules.

It's kind of hard to have you start checking stuff without the car, nor do I think the tech(s) at the dealer will take any of your technical suggestions seriously.

 

On a jeep its called a automatic shutdown relay and it does the same job as a inertia switch.

 

That's a relay not a switch. although it performs similar function but only in the sense that it provides the power to the ignition and fuel system. it cannot be reset like a switch. The PCM controls the on/off of the relay, not a little ball that moves around as you would find in an Inertia switch.

Also this would not cause the sporadic electrical glitch that he experienced with the horn and lights etc.