push button 4x4 not working...

On my 02 S10, the push button 4x4 is giving me a lot of problems. When I pushed the 4hi button, all the lights blinked and then it went back to 2hi. So, I replaced the vacuum actuator under the battery tray. The 4x4 worked for about 3 days, now it has quit again. Then I replaced the 4x4 switch inside the cab. Now when I push either button, 4 hi or 4lo, the light goes on but the front axles don't engage. In 4lo, the gearing feels much lower so I think it goes in but the front axles still don't engage. Could you tell me what is happening and/or what to replace to get the 4x4 working again??

Thanks for your time,
Jason Childress

Welcome to AF
It is computer controls just like the engine.
You need to get a transmission/transfer case/engine capable scanner on it and start with codes.
Post back any code no.
A good scanner will also have some test it can run to also pinpoint the problem.
Give us some codes and we can help.
Anything else is just throwing parts at it.
MT

Although this is not a replacement for a scanner, there are a couple things you could test.
It sounds as if the encoder motor is shifting since it is going into 4lo. A simple test would be to put it in 2hi and crawl under it and try to spin the front drive shaft. It should spin freely in 2hi. Then put it in 4hi (or 4 lo) and try to spin it. It should not spin by hand in 4hi. If that checks out ok then check for vacuum at the actuator under the battery. It should have vacuum in 4wheel. It should not have vacuum in 2 wheel. There is a vacuum switch on top of the transfer case that controls it. I have heard of them going bad due to tranny fluid. Not sure if its the correct year though. Broken and loose vacuum lines are pretty common as well.