Another Serv 4wd error, how to diagnose issue?

[Tooth]

I recently had my 2019 Jeep Sport re-geared to 4.88 with an ARB air locker in the rear. Today was my first off-road trip after break in. When I got to the trail head I put my Jeep in 4lo and the “Serv 4wd” light came on. WTF! Even though I drove 1.5 hours to wheel I turned around and left since I didn’t trust it.

I’ve read the other threads and the fix seems like it could be anything. I have no error codes just the light and the jeep won’t go in 4hi at all.

Question: I’m out of warranty so I just start replacing parts? FAD, transfer case switch, anything else? How does one diagnose the “problem” without replacing parts unnecessarily?

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[SadRobot]

What kind of OBDII reader do you have? My regular OBDII reader wasn't showing any codes but when I hooked up one of those more specific readers it told me the issue was with the transfer case position sensor. The reader I borrowed from someone had a bluetooth hookup and worked with an app on the ipad.

Turns out it was the bushing in the sensor that was causing the SERV 4WD light to go off.

 

[Tooth]

What kind of OBDII reader do you have? My regular OBDII reader wasn't showing any codes but when I hooked up one of those more specific readers it told me the issue was with the transfer case position sensor. The reader I borrowed from someone had a bluetooth hookup and worked with an app on the ipad.

Turns out it was the bushing in the sensor that was causing the SERV 4WD light to go off.

I tried a Bluetooth JScan and a regular ODB reader (see pic). Both showed no stored codes. ?

 

[SadRobot]

I tried a Bluetooth JScan and a regular ODB reader (see pic). Both showed no stored codes. ?

Hmm that's frustrating. The only other thought is that I was told the shift knobs can become loose and set off the sensor. Last time the guy from the shop got underneath the shifter and tightened something. I wasn't under there so I'm not sure exactly what he did but may be worth a look.

 

[Tooth]

Update, I got codes (pic) noting transfer case errors.

 

[19 JLUR Bright Whit3]

My guess is whoever installed your gears, f'd up the wheel sensors. I ended up killing all nannies with a Tazer Mini. Your transfer case is still mechanical, but your FAD wont engage the front axle in 4H or 4L. Since you have an ARB locker, that will still work. You could hardwire your FAD to engage/disengage or go with an FAD eliminator sleeve. (That will case more issues)

 

[Tooth]

Update: I figured out the shop that did the re-gear never programmed my jeep for the new axle ratio (3.45 to 4.88). So I updated it with my jscan, cleared the codes and so far so good. Mindful that I only drove a few hundred yards in 4low, no light….yet. ?
Thanks to everyone for the help and ideas!

 

[SadRobot]

Update: I figured out the shop that did the re-gear never programmed my jeep for the new axle ratio (3.45 to 4.88). So I updated it with my jscan, cleared the codes and so far so good. Mindful that I only drove a few hundred yards in 4low, no light….yet. ?
Thanks to everyone for the help and ideas!

I wonder what the code about the brakes were about. Hopefully the re-program is your fix.

 

[Captain Skip]

It doesn't have to be a gear install. I haven't done anything to mine other than change the TC lube oil and I got the Serv 4WD warning light. Funny thing is it's sporadic, it will come on then when I shut the Jeep off and restart it's gone. I did run my JScan on it and took screen shots of the codes it was throwing, pretty much the same as those posted above. Made an appointment at the dealership to get it taken care of while I'm still under warranty. I'll let you know what they find....if they find anything.

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