What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Mayday! C4500 4x4 stuck in 4lo

HankScorpio

HankScorpio

Customize everything
 Premium
GMOTM Winner
Joined
Dec 9, 2016
Posts
3,319
Reaction score
6,553
Location
Laramie WY
I have a 2007 C4500 4x4. Truck is stuck in 4lo after shifting itself wrong. Truck has electric t-case shift. Automatic.

I locked hubs, turned selector to 4hi, t-case shifted fine, put trans in gear and drove off down driveway in 4hi through snow. Worked great. Stopped at end of driveway, shifted trans to neutral. Turned selector to 2hi. Orange indicator blinked for a while. This means t-case did not go into 2hi. Usually if this happens (rare) I would turn knob back to 4hi, drive a couple feet and try again. This time I turned the knob back to 4hi (trans still in neutral) and the 4lo light started to flash, truck shifted to 4lo and then no orange indicator at all. Selector knob now does nothing and truck is in 4lo, which seems to work fine.

Anyone worked on one of these? I sure miss a manual lever, they work fine. Another case of options we didn't need or want from GM.
 
In my case….The shift encoder motor housing swells from corrosion and gets stuck. Shy of replacement, perhaps loosening the housing on the drivers side of the transfercase might take the pressure off the housing enough to move it. If not I think you can remove the encoder housing and manually shift the shifter fork stem.
 
You can drive the vehicle with the encoder unplugged and/or missing - there's just a service 4x4 message. The actual shifting is still a shaft sticking out of the case, just like on the old lever-shift setups, so it can be shifted with channel locks and no fluid leaks out. I put a several hundred miles on one like this to get home. The sensor inside the actuator was messed up right where "2HI" sets it, so it kept shifting into neutral while I was driving. I replaced only the sensor inside (not the whole actuator) and it's still working and shifting fine (that must have been 2016). It might be obvious by looking at it or by taking it apart. An issue with the shift controller is much less likely. The button pad can go bad, but also less likely than the actuator (any chance you got water in it?)

It might be worth a shot to disconnect the battery to let everything reset. I've also found that getting into or out of 4LO is aided by very slight movement of the vehicle.
 
Glad I read this, I have an '07 Chevy at work I just pulled into the shop that has 4 wheel drive shifting issues.
 
Blue85 said:
You can drive the vehicle with the encoder unplugged and/or missing - there's just a service 4x4 message. The actual shifting is still a shaft sticking out of the case, just like on the old lever-shift setups, so it can be shifted with channel locks and no fluid leaks out. I put a several hundred miles on one like this to get home. The sensor inside the actuator was messed up right where "2HI" sets it, so it kept shifting into neutral while I was driving. I replaced only the sensor inside (not the whole actuator) and it's still working and shifting fine (that must have been 2016). It might be obvious by looking at it or by taking it apart. An issue with the shift controller is much less likely. The button pad can go bad, but also less likely than the actuator (any chance you got water in it?)

It might be worth a shot to disconnect the battery to let everything reset. I've also found that getting into or out of 4LO is aided by very slight movement of the vehicle.
Click to expand...
Hell yeah, thats what I wanted to hear. It was dark and blizzard last night, too hard to deal with it. I need to haul a snocat about 30 miles but 4lo is too slow. (@25mph) If I can manually shift it I have until spring to fix it properly. Certainly could have had blowing snow in it. I haven't used 4wd in a while, only hauled gravel this summer and didn't need the extra traction.
 
76zimmer said:
In my case….The shift encoder motor housing swells from corrosion and gets stuck. Shy of replacement, perhaps loosening the housing on the drivers side of the transfercase might take the pressure off the housing enough to move it. If not I think you can remove the encoder housing and manually shift the shifter fork stem.
Click to expand...
Outside of a short between motor a and b circuits the diagnostic does have a check to see if the shaft in the t-case is binding.
 
I watched a video on the actuator on an 07+ truck just now and looked at the one I have and it bolts on to the rear of the tcase and has a gear that goes into the tcase and it shows you loose a little oil when you remove it so I bet that option is a no go.
I also saw I video on a reset procedure for when the battery dies and such. Mine was stuck in 4Hi after using it yesterday in the snow. You turn key to accessory then put Trans in N then hold the 4x4 knob all the way right to the neutral position for a bit. It's supposed to make a noise but I couldn't hear it in my loud shop. Then put tcase back in 2wd and Trans in park and all should be reset. I did it and mine shifts now.
 
It is a splined shaft on this one at least.
Stupid lower screw sits right in front of the torsion bar cross member. Had to use a T40 bit for a screwdriver and a 1/4" wrench to get in there.
20211228_083129.jpg
 
ZooMad75 said:
Outside of a short between motor a and b circuits the diagnostic does have a check to see if the shaft in the t-case is binding.
Click to expand...
The weird thing is that it shifted into 4lo and then the indicator lights shut off. I never turned the switch to 4lo.
 
Interesting bit of info. I called napa and there are 3 different options for the shift motor based on which tcase, at least for my late '07 2500HD 6.0L truck.
 
A 4500 would have a nvg273 t case.

I’ve had issues on the light duty knob style selector getting moved key off. Which I understand didn’t happen by your description. But follow along. Normally if the knob is moved key off the next time the truck is turned on the t-case goes to the last known range/gear and turns off the light on the knob to indicate which gear it is in.

So if the knob isn’t lit now, turn the key off and turn it back to 4hi. Turn the key back on. If the indicator comes back on it should shift. If it don’t shut the key off and move it to another position. Turn the key on. If the light comes back it should shift if not do it again and go back to the last position with the key off and turn it back on.

The system is odd because it’s only seeing the change in resistance from the knob when the key is on. If it gets moved or without the tccm seeing the change it just assumes it needs to be in the last known position whatever that is and it shifts there.

I’ve lost count how many trucks I’ve fixed on the driveway where that was the problem.

There could be some other underlying issue that caused the tccm to loose the gear value from the knob. Not sure.

Our 4500s are 2wd and we don’t see many others around here so I don’t have a lot of practical experience on the 4wd medium duty stuff.
 
ZooMad75 said:
A 4500 would have a nvg273 t case.

I’ve had issues on the light duty knob style selector getting moved key off. Which I understand didn’t happen by your description. But follow along. Normally if the knob is moved key off the next time the truck is turned on the t-case goes to the last known range/gear and turns off the light on the knob to indicate which gear it is in.

So if the knob isn’t lit now, turn the key off and turn it back to 4hi. Turn the key back on. If the indicator comes back on it should shift. If it don’t shut the key off and move it to another position. Turn the key on. If the light comes back it should shift if not do it again and go back to the last position with the key off and turn it back on.

The system is odd because it’s only seeing the change in resistance from the knob when the key is on. If it gets moved or without the tccm seeing the change it just assumes it needs to be in the last known position whatever that is and it shifts there.

I’ve lost count how many trucks I’ve fixed on the driveway where that was the problem.

There could be some other underlying issue that caused the tccm to loose the gear value from the knob. Not sure.

Our 4500s are 2wd and we don’t see many others around here so I don’t have a lot of practical experience on the 4wd medium duty stuff.
Click to expand...
I think something like you described happened. I had tried some key cycles last night but not sure of the order, didn't work. Since I knew it was in 4lo for sure I put the switch in 4lo last night when I left the shop. This morning I started it up and the 4lo indicator was on again. Drove it around the property to warm up the t-case a bit. Carefully shifted to 4hi with the trans in neutral with a slight forward roll. It worked and shifted to 4hi. Went to get gassed up, still working.

I feel like it never registered the 2wd missed shift and then when I moved the switch back to 4hi it saw that as a shift to 4lo signal. It was then confused and shut the indicator light off. Not going to try 2wd until I drop the snocat off on the mountain this afternoon. Thanks fellas!
 
You must log in or register to reply here.

Latest Posts

Top Bottom