4X4 only works sometimes

[jajehalbig]

I have a 1996 4D Chevy Tahoe. The 4X4 doesn't always engage. I've noticed that the indicator light is bright when it's willing to engage, and dim or not lit when it won't engage. What's my problem? Thanks
(I just had the rear differential oil replaced a few weeks back.)

 

[Andrew99Tahoe]

3 button or 4 button?
Either way... The first step would be to have someone with a MODIS scanner test all of the components. AAMCO offers a free tcase scan, but may say that they need it longer to look further into it and will want to charge you for labor. They tried that with me at my local shop. If you cant do that, you next step would be to troubleshoot the system one piece at the time. The nice thing about that is that there are very many steps. Even though your switch lights up, it can still be bad.(A common problem). After that would be the TCCM, transfer case control module. Its the piece under the dash, driverside left of the steering column, that clicks. Next would be your TCase motor. (Im replacing mine due to a similar issue). You also have your front axle actuator and the tcase encoder motor. Having your rear dif serviced shouldn't cause any issues. Do you have any service 4wd lights? Does your front axle actuator engage?

 

[jajehalbig]

3 button or 4 button?
Either way... The first step would be to have someone with a MODIS scanner test all of the components. AAMCO offers a free tcase scan, but may say that they need it longer to look further into it and will want to charge you for labor. They tried that with me at my local shop. If you cant do that, you next step would be to troubleshoot the system one piece at the time. The nice thing about that is that there are very many steps. Even though your switch lights up, it can still be bad.(A common problem). After that would be the TCCM, transfer case control module. Its the piece under the dash, driverside left of the steering column, that clicks. Next would be your TCase motor. (Im replacing mine due to a similar issue). You also have your front axle actuator and the tcase encoder motor. Having your rear dif serviced shouldn't cause any issues. Do you have any service 4wd lights? Does your front axle actuator engage?

Thanks for your response. I'm glad to be filled-in a little bit on the different components of the 4WD that may be causing my issue. I've replaced a TCCM on a Durango once, but to be honest I have no idea where the TCCM on my Tahoe is, or what it would look like. I'm definitley going to follow your suggestion and bring it into my local mechanic, because I have almost no clue how four-wheel-drive works, I just know I need it to work.
I've never had the service 4wd light come on before or had any codes related to drivetrain or 4x4. I'm not sure if the actuator is engaging, but when the light is on, it goes into 4 hi and 4 low with no problem. I can hear the clicking, and feel the difference upon engaing it.

 

[Jounier11]

Take it to a chevy dealer they charge 85$ but will check to see if its the actuator or any of the two switches that there are....