1997 Silverado Ext Cab 4x4 won't engage

[Sward83]

I purchased a 97 Silverado Ext Cab last Spring for my daughter. The 4x4 engaged properly at that time, but we haven't had any reason to engage it again until recent snow storms. Just my luck, the 4x4 wouldn't engage. When I press the 4hi or 4lo buttons, they only flash and the 4x4 won't engage. I've checked both the No. 2 and 24 fuses and both are fine. When I looked at the actuator, it was the updated, non-thermal version with a 3-pin connection. I don't know if it was OEM or if a prior owner had installed it. When I unplugged the actuator, it had power to the light blue wire when the 4hi button was pressed, but there was no power to the brown wire. I haven't checked with a volt meter, but from what I've read, I should have power to the brown wire whenever the key is in the "on" position. I've now exhausted my knowledge from reading many posts. Can you give me any suggestions as to what I should try next? I'd rather not take it to mechanic if it's a relatively simple fix. Thanks for any help!

[777stickman]

This sounds like the encoder motor on the t-case is not moving to the commanded position. It's a pretty common issue. The front actuator won't get any signal to engage if the t-case is not shifting.

[Sward83]

Thanks for your response. Should I first check to see if the encoder motor is getting power? How/Where do I do that?

[777stickman]

This is out of my '98 manual, so your '97 may be different.

Look for 2 connectors on the E/M, one with 6 wires & one with 2 wires. My '98 manual shows the 2 wires as red & black. With the key in the "run" position back probe these 2 wires for power with a test lite. This will take 2 people as one has to be probing while the other is pushing the selector buttons.

Keep in mind that the voltage signal to the E/M will only last 3-4 secs if the t-case control module (TCCM) does not get a feedback signal from the E/M that it moved to the commanded position. That's what the flashing lite on the selector panel is telling you.

[MikeD266]

With all of the funky routing of power in these trucks you may want to take a few minutes, pop the auto trac switch and examine the PCB for cracks as well. I've re-soldered mine twice in two different places now in the last 10 years after hairline cracks appeared.