Before anyone asks, yes I search the forum but didn’t find anything quite like I’m experiencing. Any and all help is appreciated. 1998 Tahoe with push button 4wd with auto mode. When I turn on the vehicle no warning light comes on. After I drive for about 5 to 10 min the service 4wd light comes on. Light on the 2wd button is illuminated but nothing happens when I push any of the other buttons regardless of if the service 4wd light is on or off. They do not blink or anything. Is it more likely the push button module or is it the encoder? Or is it something else. Thank you all in advance.
Service 4wd issue
- Thread starter Harvicals
- Start date
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east302
Full Access Member
You’ll need to pull the code for it. I’m not sure if parts stores will have a reader to access transfer case codes, but it’s worth asking them if they can pull the code for you.
With the code, you can look up the GM diagnostic procedure for troubleshooting it. I can pass that along if you need it.
With the code, you can look up the GM diagnostic procedure for troubleshooting it. I can pass that along if you need it.
Last edited:
Jenzenauer
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I am having a similar issue. 2006 Tahoe. Replaced the Button Panel after testing bad and then replaced the Control Module and also pulled and cleaned the ground wires. 4wd does work now and lights are illuminated as they were before the issues began. Now sporadically it will throw the Service 4wd message while driving in 2Hi and then nothing works. If you turn off the key and restart then you can operate the transfer case as normal via the buttons but once the message pops up it will not work until you turn off the key and restart.
Is this the Auto 4x4?
How was the switch tested? Were the modes ohmed to confirm proper values?
It would be best to read the 4x4 code when it happens; there also may be a stored code to read later.
How was the switch tested? Were the modes ohmed to confirm proper values?
It would be best to read the 4x4 code when it happens; there also may be a stored code to read later.
Current codes are always best but I used to love going looking for History or Stored codes to really get in the nitty gritty and make sure the problem did not come back.
Jenzenauer
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Yes it has the Auto 4wd button. I have never used it before and drive in 2Hi normally. Seems to happen more often after I have used 4Hi or 4Lo then the next time or two when I drive it the Service 4wd message will pop up.
Ohmed the switch to confirm it was bad before I replaced it. I have not taken it in to the shop to have the TC read yet.
Ohmed the switch to confirm it was bad before I replaced it. I have not taken it in to the shop to have the TC read yet.
Others can come up with a problem like this so please let us know what the shop finds. Please don't allow a tech to just say, "this part is bad". Ask why it is bad and share here.
jeff ashworth
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From what I have read on these problems because I'm having them also, is the push button switch when you start the vehicle it will toggle through all the lights in the push button and stop on the one you have it set on if it is good and if the T-case control module is good, the only one I have not replaced is the T-case control module, and is all this true or did I miss read it.
Just thought I'd toss this in here. On 3 different vehicles in 2019 I fixed these issues by replacing the sensor inside the transfer case shift motor that is responsible for reporting the current position of the transfer case shift motor. My 2005 Yukon SLT, my 2002 TrailBlazer, and a brother in laws 2004 Envoy all suffered the very same occasional flashing selector switch lights and service 4wd light. For the 2005 Yukon with NP8 RPO the part is #88962315.
This sensor can erode the resistive material of the sensor as seen in the pictures I will attempt to include here. If this sensor doesn't return a steady voltage back to the tccm the shift will fail. The picture which shows the internal sensor pickups shows a buildup of crud that surely would impede the return of a steady voltage
signal. I see many folks replace the entire shift motor and for many this may be the best approach though for myself I prefer this lesser cost item once the actual fault is proven to my satisfaction with either my tech 2 or a DMM. Naturally any repair of this type requires all gear teeth and such to be kept in their same position. Thus you should mark gear teeth etc to be absolutely certain they will be replaced in the rightful position on re-assembly.
This sensor can erode the resistive material of the sensor as seen in the pictures I will attempt to include here. If this sensor doesn't return a steady voltage back to the tccm the shift will fail. The picture which shows the internal sensor pickups shows a buildup of crud that surely would impede the return of a steady voltage
signal. I see many folks replace the entire shift motor and for many this may be the best approach though for myself I prefer this lesser cost item once the actual fault is proven to my satisfaction with either my tech 2 or a DMM. Naturally any repair of this type requires all gear teeth and such to be kept in their same position. Thus you should mark gear teeth etc to be absolutely certain they will be replaced in the rightful position on re-assembly.
I have 99 tahoe, was having a similar problem.. when I would crank the truck the 4x4 low would start to blink and then shift into low.. if i was to put in gear before it shifted i was ok. Eventually I did replaced my switch and actuator. Light stayed off for a while now it comes on after I drive for a bit. Am still able to shift into all modes though. I just said the heck with it. The actuator and switch are both easy fixes. I hope my issue is not the module.
