One of the more notorious error Jeep error messages is “Service 4WD System.” It doesn’t help that Chrysler/Stellantis tied about 50 different codes to that message. When it comes to electronics, this pair of companies can F-up a steel ball with a rubber hammer. No way in Hell I’m ever buying an EV or Hybrid from any of the Stellantis brands!

Shotty electrical design and components has been a trademark of Chrysler since before the 1990 Jeep Grand Wagoneer came out.

1990 Jeep Grand Wagoneer

Loved mine though the volt meter on the dash existed for entertainment purposes only. Turn on the headlights, it barely wiggled. Turn on the blower motor for the heat, drops down almost to discharge. Fan was on a 10AMP fuse. Headlights had something like a 60AMP relay. Nice design dudes!

Misinformation

You can find a long thread here branching to other threads and ponderings. It’s not meant to be misinformation, it just is . . . most of the time. You will even find some things mentioned which approach the plucked rooster anus cure for rabies level of fantastic. (I kid you not, that’s a thing, listen to the Radiolab episode.)

One such “cure” is to pull fuse 25 FCDM, drive around a bit, then replace the fuse. It has about the same level of success as the plucked rooster anus which, surprisingly, is not zero.

One poor bastard had all of this done until he got to the last one.

  • LIMITED SLIP SENSOR IN AXLE
  • STEERING ANGLE SENSOR
  • SOLENOID IN DIFF
  • SHORTED OUT CONTROL WIRE GOING INTO THE REAR DIFF THE COMPONENT INSIDE THE DIFF WAS REPLACED INCLUDING WIRING
  • SENSOR ON TRANSFER CASE
  • ABS MODULE REPLACED
  • (FDCM) FINAL DRIVE CONTROL MODULE
  • TRANSFER CASE MOTOR
  • BRAKE LIGHT SWITCH
  • The service 4 wheel drive light came on intermittently for about a year. Jeep changed transmission sensors, axle sensors, re flashed the computers several times without any permanent fix. Finally I asked Jeep to trace the wiring harness and to check the resistance because the problem acted like a wire was grounding out. The dealership set some time aside to do this and they found a wire grounding out under the transmission housing, repaired it and it was the fix needed.

No, they never expounded on just where that “wire” was. They also never came back.

You Should Already Have

One of these or something just like it.

Codes scanner

I bought this thing from Harbor Freight years ago for under $50. The newest vehicle I drive is a 2006 so I really don’t have to update the software very often. This one can clear non-permanent codes, show you some OEM codes, and run some system tests. I’m sure they’ve come down in price because I’ve had this one for over a decade.

If You Have a Code

Unless it is an improper voltage code, it is most likely bullshit. Somewhere underneath connecting to the transmission will be a plug much like this one.

When you take it out and look at it you will most likely find corrosion like this or worse. Corrosion here causes all kinds of bizarre codes to be thrown and hapless Jeep owners to replace a whole lot of sensors/parts that have nothing wrong. If you drive your Jeep in a lot of road salt, go mudding, or live near the ocean, you connector looks like this. Dielectric grease is your friend.

Clear all of your codes and drive for a while. Wait to see if the problem comes back.

You Don’t Have a Code

Welcome to the vast majority!

Stop buying batteries at Walmart!

You aren’t saving money buying a cheap battery. Yes, Die Hard batteries can be $400.

They cost that much for a reason! That battery you paid $100 for is going to cost you over a thousand dollars in repairs. Many dollars will be replacing perfectly functioning parts tracing this very problem. Those “store brand” North Korean knock-offs don’t put out proper voltage for long, if at all. They are price around a hundred dollars for a reason.

My Story

I bought my 2006 Jeep Commander from a dealer around Des Moines, IA this past spring/summer. Had it trucked out to the farm in Illinois. When I popped the hood I saw a nearly brand new never-heard-of-it brand battery. Rolled right over to start so I thought nothing of it. Big mistake.

It’s November now, but I didn’t make it three months before I started seeing “Service 4WD System” error messages. After finding all of the plucked rooster anus “cures” for this problem I waited until my local mechanic had time. (I was helping with harvest and couldn’t really dig into it.)

He put the best Interstate battery he had in it. Service 4WD System message went away along with many other electrical gremlins. My knock-off battery did me the favor of throwing “voltage out of range” error codes all over the place.

Why Have I Not Had This Problem With My 2002?

Despite Jeep owners wailing about this as a universal Jeep problem, I’ve never had the issue with my 2002 Jeep Grand Cherokee Overland. Why? I never buy a cheap battery. That thing had 113K on it when I bought it. Today it is less than one oil change away from 200K.

One of the most expensive things you can buy is a cheap battery.