My 1999 Chevy Tahoe is not switching into 4wd.

[oknik123]

Okay, where to start..... I have a 99 hoe and it's giving me a few problems. When I push the switch for 4w hi, 4 lo, or all wheel, it just blinks at me. It doesn't engage in the front diff but in 4 lo it engages in the transfer case. I can hear it click in the transfer case. I posted a similar post and someone said that it could be the actuator so I tried to replace that and nothing happened. The switch just blinks. I put a volt meter on the plug that plugs into the actuator and it only has 1 volt going to it. Is that normal? Also, I tested to see if the front drive shaft turned when it was in 4 hi and when I put it back in 2 hi it did turn really fast... is that normal?
Now, I'm about to get rid of the actuator all together and just put a Posi Lok in instead of the actuator. Does anyone know if that would fix my problem? What do you think? Any suggestions would help.

 

[SunlitComet]

The controller is not seeing a completed shift hence the blinking for about 30 seconds and then auto disengagement. What t-case model are you running? Drive shaft is normal just need to find the circuit or switch at fault for the actuator not getting volts.

 

[oknik123]

I'm not sure about the transfer case model and the plug to the actuator is getting like 1 volt or 1 in a half volts.... is that normal?

 

[SunlitComet]

Quickway to find out is call a gm dealer ask for parts give them the vin number to decode and ask them which one you have or the rpo code for it. If you visit them they will give you a build sheet on your vehicle that has all the equipment installed.

I would rather know first before have to multiple diagrams and charts for several t-cases


report back and let the fun began.

 

[FireManDave]

same probelm

I thknk im having the same issue, just a different year

1996 chevy tahoe, 350, auto, push button(3 button)

I can not shift into 4 wheel drive while moving.
I can from 2wd to 4lo but no 4hi. The 4hiand 4lo lights will flash when i push 4hi button.
I can not shift into 4hi without pulling the t-case fuse(#2), after everything resets it will then allow me to shift into 4 hi. No matter what position the t-case is in the light in the switch will flash(2wd, 4hi, 4lo). I have noticed that when im in 2wd the 4hi will flash. Im not sure of the pattern of the light flashing. I do have a passenger side speed sensor out( Unplugged for right now), im not sure if this maybe causing some of my problems. Also i believe that my truck still has the thermal actuator in the front.
I know that in 4lo and 4hi the front drive train engages after i reset the t-case.



Im not sure if im leaving anything out.

 

[SunlitComet]

Please perform this operation and report back please

Displaying Diagnostic Trouble Codes

1. Install jumper wire between DLC terminal 13 and ground, Fig. 25 . The DLC is located under the lefthand side of the instrument panel, right of the steering column.
2. Turn ignition switch to On position.
3. Wait three seconds, then observe transfer case switch status lamps.

Reading Diagnostic Trouble Codes
The transfer case status lamps will flash to indicate the DTC's stored in memory. If only one DTC is stored in memory, that DTC flashes repeatedly with a three second delay between flash sequences. If more than one DTC is stored in memory, the first DTC flashes once, then the next code is flashed. This sequence continues to flash until the jumper wire is disconnected.

 

[SunlitComet]

picture

 

[SunlitComet]

Also before you do try your 4hi setting at least eight times and do not pull any 4wd fuses before trying or after until you have extracted the codes. Otherwise you will wipe it's memory I am pretty sure what the problem is but would like the code to verify first.

 

[FireManDave]

I have a code of 2

 

[SunlitComet]

From another thread I am helping with:


That is what I figured. When the encoder assy on the shift motor gives errors on it's current shift position it goes into it limp mode and locks out 4hi dileberately. Disconnect the six way plug from the encoder and follow the test below. Start on step 2 and if you end up on step 3 and answering yes that confirms the shift motor assy needs to be replaced. If not we will tackcle it further.
The motor assy is located on the left side front structure of the t-case. 6-way connector facing righton bottom of unit, motor connector facing left.

Right when you are ready to take the motor out pull fuses #2 & #4 and reinsert them after. This will wipe out the lock out function and after your done start enigine and try a few shifts.