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4 wheel drive problem

I have a 1995 GMC Sierra SL, extended cab with a 5.0 litre engine. Recently, I tried engaging 4 wheel high. The light did not come on the floor shifter, and it did not sound or feel like it engaged. I tried 4 wheel low, and it worked. I checked all the fuses and they tested good. I used 4 wheel high about a month ago without issue. Can you provide guidance on what I can look for next.

Get in the dirt and make sure it is not working.
If not look for vacuum leaks,I maybe wrong but think it is vac controlled.

Thank you for replying. You are correct. It is vacuum controlled. Vacuum line is good. 4 wheel high is out for sure. I assumed if vacuum was out, neither 4 wheel high or low would work. Thanks again for your input.

I have a 2000 S10 Blazer with push button 4wd. The push buttons control the Transfer Case Control Module which in turn signals the encoder motor on the transfer case to shift in and out of 4wd. If I don’t shift into 4wd for any length of time the TCCM has to be reset by disconnecting the battery.

I’m assuming the floor shifter on your truck is a mechanical linkage though. On the other hand, the front axles are engaged by a vacuum actuator. It’s under the battery tray on the Blazer. The actuator is controlled by a vacuum switch on the Blazer’s firewall.

The vacuum switch failed on the Blazer. The transfer case would shift properly, but the front axles would not engage and the 4wd drive light continued blinking. The switch can be checked by disconnecting the vacuum lines from the switch and connecting them. If vacuum is present and the shifter is moved to 4wd the axles should engage.

Ed B.

Sorry about spelling but Try research transfer case cylinoid

It’s spelled solenoid.

It is a manual shift on the floor. I did notice a rubber line attached to the transfer case, and assumed it was for vacuum. I’ll try to find the vacuum switch. Thank you, much appreciated.

I noticed a switch, solenoid or some type of sending unit on the top front (engine side) of the transfer case, and one that looks just like it on the side and rear of the transfer case. I heard one might be a speed sensor, the other ??? Thank you as well. Much appreciated.