On a 2003 Avalanche with push button 4wd,

A common issue with the push button style 4x4 is that the retaining clip in the transfer case comes off of the shaft and allows the actuator to slip in and out of position. I recommend pulling the solenoid out and inspecting it.

Best,

Joe

I have a 1994 4x4 Suburban. In mine, there's a stick on the hump in the floor, and I'm sure this is the case with yours too. This year model does not require that you get out and lock your wheel hubs. There are labels that are supposed to light up to tell you if you're in 2wd, 4wdHigh, or 2wdLow, but mine don't seem to work. If it's dark out and I can't see the labels, I just have to remember that 4wd High is all the way towards me, 4wd Low is all the way forward, and 2wd in sort of in the middle (but closer to me than the actual middle).

To shift into 4wd High (which is what you'll use for most purposes, like driving in bad weather), just pull that stick back towards you in one swift motion. You can do this while you're parked or while driving forward down the highway.

To shift back out of 4wd High and into 2wd, just push that stick forward a little bit, to where it was before.

To shift into 4wd Low (which is what you'll use only for extreme conditions, like off-road mudding or getting out of your driveway in super deep snow), you have to be stopped. You can NOT just shift into 4wd Low while you're going down the road. First, put it into Neutral (with the shifter on the steering column), Then push that stick on the floor all the way forward. Mine is hard to push, so I use my foot.

To shift back into 2wd from 4wd Low, you need to be stopped and in Neutral also. Pull the stick back towards you to the same position it was in before. (Not all the way towards you, or you'll be in 4wd High instead of 2wd.)

Hope that helps.

Could be several different problems - first step is to check for error codes (DTCs) and follow up if any.

probaly a broken rear/lower planetary set or ring gear is broke

check the 4WD shift motor on the transfer case

If you need further help, I’m available over the phone at https://www.6ya.com/expert/david_4c166ba81493f541

Check the fuse to your 4wd at the fuse panel at the end of the dash drivers side. If the fuse is good, put the transmission in neutral and listen for the Transfer case encoder motor to work when you push the button on the dash for 4wd hi then to 2wd. If you do not hear it working, inspect the wire harness at the Encoder motor to make sure there not damaged in anyway due to corrosion or disconnected.
Here's some info on how the 4wd system operates on newer Blazers for all those searching for the cause of the flashing dash switch light and no engagement.

4WD System Operation on 98 up (2nd Generation) Blazers/Jimmies

The front drive shaft always turns on “shift on the fly” systems so the drive train is at the same speed in the front as the rear or the whole thing would break when engaging 4Hi or Autotrac when moving. InstaTrac (NV243 case or NP1) has 3 buttons. AutoTrac (NV246 case or NP8) has 4 buttons and clutch packs in the transfer case and is the only system for on pavement driving! Prior were the NV231 (87-93) lever and NP233 (94-97) electric motor. Your VIN # is the only sure way the dealer can get correct parts/listings!
1. Select mode on dash switch
2. Signal goes to the Transfer case control module (TCCM) or computer located in the cab on the passenger side behind the kick panel.
3. If you want 4 Lo the TCCM commands the encoder motor on the transfer case to switch a lower gear in (requires putting the shifter in Neutral and be stopped or only going 2-3mph). Note that if 4 Hi selected no action done in the transfer case. The transfer case is chain coupled and has the low and high gear. You can put all systems into Neutral by pushing the 2Hi and 4Lo button at the same time when the key is in the run position (or running but not off or acc).
4. The left front (drivers side) CV axle is always engaged to the front differential, but the right side is not coupled in 2wd. There is an actuator located under the battery tray that when commanded is vacuum actuated and pulls a cable from it to the right side CV axle coupler engaging that axle. A sensor is on that axle that tells the TCCM the axle position.
5. On 99up there is an additional vacuum switch on the firewall that switches the vacuum on and signals the TCCM also.
6. The dash light on the selector switch flashes while all this is occurring and will not switch out of 2wd unless all parts report correctly – same on the switch to any mode or back to 2wd.

So, there are a lot of possible failure areas with actuators/computer/motor/sensors/vac hoses and a special scanner is required to read the codes when the Service 4WD light comes on. But, a few things can easily be done before going to the dealer.
1. Check all vacuum hoses from the intake to the drivers side reservoir can, then to the extra switch (99up) and down to the under battery actuator. Small hose is 5/32 and larger is 7/32”.
2. See if the actuator pulls the front axle cable to engage it. If not and all hoses are good the diaphragm may be leaking on the actuator. If it engages but the light is still flashing remove the indicator switch on the front axle (only electrical plug in there) and manually push it in with the connector plugged in and see if the light stops, if so replace.
3. Listen to the encoder motor clunk when 4 Lo selected. If not working look at the wiring going to it for any cuts/breaks and repair if any found. Another indicator switch on top of this case. The fluid in the AutoTrac case should be the newer light blue Autotrak –II synthetic P/N 12378508 ($7 qt) not the red Dexron III.
4. If the light keeps flashing after this then disconnect the battery for 30 minutes for a TCCM reset, just make sure you turn off your radio first.
5. Still not working – take it to the dealer and stop at the bank on the way for $$$$!
12577412 is the part number for the Transfer Case Control Module (TCCM), or you can do the Salvage Yard for $15.00 if that's the part that has gone bad.

those pushbutton switches are known to be bad, local wrecker should be able to supply you one .

8/19/2009 I had this problem and it cost me 2700.00 to repair the truck. The problem is the "encoder Modual" that controls the 2/4 system. Unfortunately I did not know and my rear end needed to be repaired. The encoder cost about 388.00 at the dealer, good luck

possible range selection detent switch not working causing to get stuck some times in one range only and wont shift to other range 4wd light in dash just keeps flashing for about 10 seconds then goes to previous state this then can jam up 2wd 4wd lever that you then cannot move.
there are 3 switches 2 on trans/transferr case, 1 on front LH diff axle tube actuator (shift on fly). can cause damge to the electric actuator then on transferr case.
suggest you get a dealer to look at or some one that knows this system. is also vaccum operated on front diff shift on fly unit and there were 2 different systems fitted to these vehicles push button 4wd on dash and lever next to gear lever which i take is yours

Some one told me to unhook the batery for half an hour then hook it back up and try it. Well it worked,no more shif problems.