93 S10 Blazer 4x4 problems...

93 S10 Blazer 4x4 4.3L Vortec automatic

Out of the blue, the 4 wheel drive is not engaging. It happened suddenly and i get the feeling it may be an electrical part now. The light indicator down below goes on to signify which you are in, i.e. 2 wheel, 4high, N, 4low. But the chassis icon on the right of that doesn't like up anymore as it did previously. It would light up the front part of the chassis on that icon when in 4 wheel. Now, it's not.

I blindly put in a vacuum actuator because these generally need replacing. That made no difference. The vacuum line from the actuator has a "T" in it, part goes down below and part runs into a switch up along side the battery on the inner fender (kinda like a coolant temp sensor type) and then it has a plug into an electical line. What switch is that? There is also another switch down below on the transfer case, which I'm guessing is the vacuum switch. I want to locate the vacuum solenoid, anyone know where that is? That may be the problem.

When checking vacuum at actuator, when vehicle is in 4high and running in park, should there be noticeable vacuum from that line? Just wondering how to check the vacuum?

Thanks for the ideas.

The sensor by the battery was installed as a recall to all those trucks in roughly those years. Basiclly it tells the ABS system when the truck is 4WD/2WD and the system was recalibrated as required. To not have the front part of the 4x4 system light up at the shift lever is indicating the front differential is not engaging for some reason. If you have a vaccuum guage, disconnect the line at the actuator under the battery tray and connect the vaccuum line to your guage. Shift the truck into 4x4, you should notice vacuum at this point. If there is no vaccuum, trace the vaccuum line to the transfer case. Look for cracks, leaks etc. If you do get vaccuum, take a look at the actuator and make sure it is not damaged, make sure it is "pulling" the cable to engage the front differential.

The sensor by the battery was installed as a recall to all those trucks in roughly those years. Basiclly it tells the ABS system when the truck is 4WD/2WD and the system was recalibrated as required. To not have the front part of the 4x4 system light up at the shift lever is indicating the front differential is not engaging for some reason. If you have a vaccuum guage, disconnect the line at the actuator under the battery tray and connect the vaccuum line to your guage. Shift the truck into 4x4, you should notice vacuum at this point. If there is no vaccuum, trace the vaccuum line to the transfer case. Look for cracks, leaks etc. If you do get vaccuum, take a look at the actuator and make sure it is not damaged, make sure it is "pulling" the cable to engage the front differential.

Thanks, I put a new actuator in, but that's something I can check. Can you manually pull that cable to engage/disengage 4 wheel?

Can you manually pull that cable to engage/disengage 4 wheel?

Yes, pull it and with vise grip lightly lock it there. Essentially youve locked up the front diff. The light should and if working properly will stay on even if its in 4wd.

Yes, pull it and with vise grip lightly lock it there. Essentially youve locked up the front diff. The light should and if working properly will stay on even if its in 4wd.

Ok, I'm working on it now. I put the old actuator back in because it is getting vacuum and sucking up on the cable, but still no little chassis light to signify 4wheel and no 4wheel drive yet. Just the little dot light to signify that it is shifted into 4wheel, when it really isn't engaging. I see the diaphram of the actuator sucking in, so that's good. I tried pulling on the cable briefly to see if it sounded like it was engaging, but I didn't hear anything. Maybe I need to use the vice grips like you said and try that.

Since I'm getting vacuum to the actuator, that must mean the solenoid is good, if it is before it. But with vacuum and no 4wheel, could it be a bad vacuum switch mounted on the differential? I think I'm going to get one ($15) and see if that does the trick. But I'd like to know your thoughts as well. I don't believe there is a vacuum leak from what I have seen. This seems very much like an electrical/sensor/switch issue.

What are your thoughts?
Thank you as well.

I got a new transfer case vacuum switch and put it in. The old one has the ball stuck inward on it. The new one went in rather hard, was hoping it didn't get cross threaded because it's such a tight area. Tried the 4wheel and again no little chassis light up or 4 wheel drive. I may take that switch out again just to make sure it is in properly. If that isn't the problem, I guess the next thing is the vacuum solenoid. Anyone know where that one is located? Diagram points toward front, but not specific.