Hello, I have a problem , and hoping I can get some helpful advice. I own a 1999 3/4 ton sierra 6.5 litre diesel. 4x4 push button. the front axle actuator is electronic.
When I push the 4hi or 4 low button, the lights just blink, don't stay on solid.
when I push the 4hi or 4 low the solenoid on the transfer case engages and turns the propshaft, but I don't hear the front axle actuator do anything.

so I disconnected the plug from the front actuator, there are 4 wires going to it. the axle switch signal, axle actuator - control, Ignition voltage, and ground.

I got power on Ignition voltage, and I got good ground on the ground wire and axle switch signal.

but I got no power from the Axle actuator - control having it in 4hi, 4low, 2 wheel drive.

in my schmatic, it shows the front axle actuator, it shows the motor with solid state written below it. I am wondering what they ment by solid state and which way would the power travel on the axle actuator control wire.
if it travels out of the front axle actuator to the transfer case shift control module or from the Transfer case shift control module to the front axle actuator? if anyone can help me out on this, Thanks! ,

Solid state means that it is electronic. Replace it!

ok. I put direct power from battery to front axle actuator. and I can hear it operate. I check transfer case module, it's ok. I check for codes, no codes.

lights still blink in 4 hi or 4 low. if front axle actuator, transfer case module are good and there are no codes. does anyone know what else could be causing the front axle not to engage?

The push button switch is a common problem. Another piece of shoddy Dephi parts.

I replace the front axle actuator. and 4x4 works now. woo hoo!!