4WD Won’t Shift Back to 2HI

[spacklesworth]

Howdy,

I have the 4-button (2HI, 4Auto, 4HI, 4LO) system in my ‘98 K2500 Suburban and am having issues shifting from anything 4 back to 2HI. I have no problems shifting from 2HI to anything 4, but after driving in 4 for about 50-100yds the “Service 4WD” light appears in the cluster, although the system seems to be working fine as far as I can tell and no strange noises can be heard.

The problem occurs when trying to switch from anything 4 back to 2HI. The 2HI button will flash as if it’s switching back, but then the solid light will return to whichever 4 setting it was in. I’ve found I can get around this by turning the whole truck off, then starting it again which removes the “Service 4WD” light and allows me to switch back to 2HI with no problems.

Has anyone else experienced this or know what this could be? The workaround I mentioned where I shut the truck off and start it again seems to work for now, but I hope to get to the source and fix it properly. Thanks!

 

[b454rat]

There are only 3 pieces to the electronic shift crap. The buttons on the dash, the shift motor on te t-case, and the actuator in the front diff. Sounds like the motor is not letting it return or shift. Try n grab one from a junk yard and see what happens. I wanna say this is what my old Tahoe would do. Took about half n hour to shift into 4wd, but IIRC would go back soon as hit the 2wd button.

 

[spacklesworth]

There are only 3 pieces to the electronic shift crap. The buttons on the dash, the shift motor on te t-case, and the actuator in the front diff. Sounds like the motor is not letting it return or shift. Try n grab one from a junk yard and see what happens. I wanna say this is what my old Tahoe would do. Took about half n hour to shift into 4wd, but IIRC would go back soon as hit the 2wd button.

Thanks, I’ll look more into finding a shift motor. I had to use the 4WD today and managed to go a good distance without the service light coming on and thought the issue had somehow fixed itself, but low and behold it came back.

 

[Anthony Christie]

Ah yes! I too live in that dream world where stuff fixes itself...I know it well! I Hope the suggested fix works! If I can piggyback on your thread (I'm new to this site, having just bought my first two of these awesome trucks, so I don't really know protocols), I'm having transfer case system problems similar to those described by b454rat (he's awesome), above. In my '93 pickup (2500 Silverado HD, 6.5 Turbo-Diesel) most often, when I shift the floor lever from 2wd to either range of 4wd, nothing happens. Occasionally all works as it should; front axle engages, indicator lights on the floor mounted shift-lever console come cheerily on, and I get the heavy beast out of the slippery bit it's stuck in. When I shift back to 2wd, it does it perfectly, but soon refuses again to go back to 4wd. Intermittent. Anyone know what to look at first, second, third, etc., in terms of making a good diagnosis? Thanks. (Also. any help with how better to use this forum appreciated and apologies for this intrusion into the thread.)

 

[b454rat]

I your having issues with a lever 4wd, then it's the actuator on the front axle. In extreme cases could be the wiring, since that's all it is between the lever and the actuator. Lever is mechanical, so either works or don't lol

 

[Anthony Christie]

Actuator... OK! Thanks!

 

[thinger2]

The pushbutton and the lever t case both have a transfer case switch and there is a technical service bulliten about 4x4 and 2 wheel shift problems associated with that switch that im pretty sure extends through the 98.
As I recall the TSB also mentions "false" dtc codes being set and codes temporary clearing at restart only to come back later.
Transfer case switch feeds to the ECM
Good news is a tranfer case switch is cheap and easy to replace
Like 40 bucks.
I would check that and its wiring first

 

[Anthony Christie]

Aha! I will do that. Thanks! I would be curious to see that (and any other) TSB. Would you know where I could find such things? Would it be archived online somewhere? GM website?

 

[Anthony Christie]

Never mind. Googled it. https://www.tsbsearch.com/Chevrolet?Page=6