4wd front actuator will disengage but not engage

I have a weird 4wd actuator issue (2000 access cab limited). The 4wd will not engage, but it will disengage. I recently bought it and it came with 3 extra actuators. I took one of the spares apart to manually engage it, I plugged it into the harness and the truck will disengage it, but it will not engage Has anybody else run into this issue? TIA

 

I have this exact same issue. My truck, also a 2000 access cab limited, does the same thing. I have replaced both the actuator and the 4wd computer, to no avail. I'm assuming it's an issue with the wiring somewhere, I don't have the time, knowledge, or money to diagnose it right now. Since the motor will shift out of 4wd, but not in, that likely means that the position sensors inside of the actuator are working correctly.

You can test functionality of the actuator by removing it and connecting pins 2 and 6 to power and ground. Reversing the polarity of those two pins will move the shift fork in the opposite direction.

Make sure to update us if you figure it out!

 

Check the leads at the switch and trace the wire looking for corrosion or chafing.

 

I noticed the other day that the ABS sensor wires on the front hubs had been cut. Could the lack of a signal from the ABS sensor be in any way involved?

 

One way to find out … and if it’s the case, this could be the big “AHA!” missing link that solves this issue for multiple people.

 

I don't think so. My truck doesn't have ABS (despite being a limited with every other option!) and I think it should be able to function without it. Plenty of these trucks were sold with 4wd and without ABS too.

I wonder if that wire is to tell the ABS module something like "hey, all four wheels are connected so the front wheel speed should match the rear" or something like that. I have no idea.

 

Please don’t beat me for bringing 2nd gen comment to a 1st gen thread. But it might help.


On my 08, it went into 4WD fine but wouldn’t come out. Ended up being one wire from the 4WD ECU to ADD had been chewed in two. I found it by checking continuity between the ECU connector and the ADD connector. Then, I just happened to see the wire broken when I was tracing the harness.

 

It's good info, we actually had two others in the 1st gen section who had same/similar. Wiring damage on one, bent pin on another.

 

No. i removed the Abs sensors from the front hubs on my 2004 and it shifts in and out of 4wd just fine.

 

I tested the voltage from the ECU to see if maybe the red-white wire wasn't putting enough voltage through to be able to shift the actuator into 4WD. I found that both the red-white wire and the light green wire (pins 2 and 6) get power when I disengage the 4WD button but neither of them get any kind of power when I engage the 4WD button. This leads me to believe that the 4WD ECU is bad and needs replacing. Am I on the right path?

 

That makes sense in my head, but be warned: I purchased a new 4WD ECU and it didn't solve my issue. I didn't test nearly as in depth as you have, but when pressing the 4WD button I heard 5-8 repeated clicks from the relays in the ECU. This seemed off to me, but the new-used $110 ECU did the exact same thing. Can you hear your relays click when you press the button?

It definitely seems like the ECU is being commanded to shift, I'd be surprised if the issue was related to the switch or the wiring between it and the ECU. Just thinking aloud here, but could the wires between the ECU and the position switches have a break? Have you looked at the FSM? I know there's a procedure to test the transfer case switches but I'm not sure bout the ADD.

I'd be willing to ship you the spare ECU I have (also from a 2000) but I might not be able to get it sent out until I get home from college in three weeks.

 

Well, if you're already that deep into to electrics, this video will get there I'm sure:

https://youtu.be/TmuEVv1neVQ

 

Thank you! That is very kind. I am going to try taking everything apart first and cleaning up the leads and cleaning the contact areas just be sure. I should be able to get to it before you get home for winter break, I'll keep you updated.

I have watched the video, it leads me to believe that it could potentially be the transfer case actuator. I can hear it actuating and can see that the front drive shaft rotates when the 4wd button is depressed. I figure its better to make sure everything is clean and lubed up before I go replacing the ECU.