4wd Trouble shooting

[jrawk1120]

I have a 1999 tahoe obs 4dr 4wd. The service 4wd light is on. It will not engage, if I press 4 low, it just blinks and goes back to 2wd. If I press 4hi, it will sometimes say its in 4hi, but dont actually hear any movement, and it doesn't actually engage. sometimes the lights are off, sometimes they are on. Any way I can diagnose the problem before taking it to a mechanic?

 

[blueflamed03]

actuator

---------- Post added at 08:49 PM ---------- Previous post was at 08:48 PM ----------

http://www.tahoeyukonforum.com/forum/showthread.php?t=17964&highlight=wheel+drive+actuator

 

[SunlitComet]

The 99 actually use diag codes becuase there is a lot to process. When you go into low 4 are you in nuetral moving less then 3mph. With out the scanner reading the 99's are difficult to pindown to a definite cause. Venturing a guess I would say something is either wrong in the shift motor/encoder assy or your shifting is binding, loose or broken. if the 4hi light stays on steady then the front axle actuator appears to working coreectly when switched on by the other components. If you use proper procedures to shift into lo and no change in lights than control circuits have problems which will illuminate the service light. There are 16 related codes for diagnosis. Can you give anymore details. What lights remain on or off and after what button is pressed? Things like that. Lay it on me.

 

[jrawk1120]

Well if I hit 4hi, the light will sometimes stay on 4hi, or just switched back to 2wd. It will not go into 4lo. If I hit 4lo, it'll blink a few times, and either go back to 2wd or the switches wiill just turn off. I am alwags in nuetral when going into 4wd, and am usually stopped. If It happens to go into 4wd (but not work) and I switch back to 2wd, its instant.

 

[SunlitComet]

Motor control seems to be operating properly. I would proceed to get help with someone who has a proper scanner, like a tranny shop since it is a gear box, to pull what appears to be an active code from your control module. It seems like your shifting mechanism inside is at fualt or the encoder on the shift motor encoder is malfunctioning causing an automatic fall back.

Your front axle mechanism will not be instructed to engage until it sees a completed shift in the tcase so if it never makes it to 4lo it won't even bother trying to lock the front axle.

You can't diagnose these like the models a few years earlier. That being said if you get an ocassional 4hi but no 4lo tcase switch over especially with no light at all something has got to be wrong internally or something electronically is wrong. If these was a 96-97 it would be a piece of cake.

Pulling the error code is the proper next step. Try a parts store to see if they do free scan and specifically if the scanner is capable of communicating with the tcase module aka TCCM. If not tranny shop is next best and low cost choice. If not there then the dealer TECH 2 scanner will have to be used.

If you have anymore details feel free to pass them on.

 

[jrawk1120]

Actuator motor not working. I took it to a buddy of mine. The 4hi works, auto 4wd works, but 4lo does not work. He said he could fix it for $500, and said since I don't do any off roading, and only use 4 wheel to get outta my driveway, that it really isn't necessary to fix. I don't plan on putting the truck on the market anytime soon, if ever.

Any insight on this?

 

[SunlitComet]

How did your friend determine this exactly? or you talking axle actuator or transfer case actuator if 4hi and auto work your front axle actuator should not be the problem. If it is your t-case motor you can get them from Amazon for less then $150. It is simple to do.