Yesterday I bought an '06 4Runner SR5 V8 4WD, my third T4R, from a couple who never used it offroad and with only 30K miles on it. Unfortunately I didn't fully test the 4WD system, and found out today that the center diff lock will not engage. This model has the always on H4 mode, and you can switch that to L4, which works flawlessly. But I can't get the center diff to lock in either mode. I tried engaging it in Park, Neutral, and Drive, both moving and not moving. All it does is flash the center diff lock indicator on the cluster, it never goes solid which per the manual would indicate it had successfully engaged.

After doing some Googling I found that this issue can occur when the system is infrequently or never used - the center diff lock actuator can get stuck or gummed up. I had my wife press the diff lock button while I was under the car, and when she does I can hear the actuator attached to the center diff (circled in the pic below) beeping about once every second. I tried banging on the black actuator box, a bit with a rubber mallet while she tried pressing/holding in the button but no dice.

Has anyone else had this issue? Any tips on fixing it short of pulling the diff apart and replacing the actuator? And am I banging on the correct part? Any help appreciated!

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This is a fairly common issue. You are tapping the correct part with the mallet. If that doesn't work then you'll need a new actuator which is a $2500 fix, give or take. Keep at it with the mallet. Hopefully you can get it to wake up.

If you do get it working...be sure to exercise it frequently. It's a use it or lose it kinda deal with these trucks.

first I'd try taking a 12mm wrench and slightly loosen the Qty-3 actuator bolts just enough to jiggle the actuator a bit then re-tighten.

Sometimes the actuator rod gets gummed up from lack of use.

Ya, alot of guys have had luck loosening the 3 bolts holding the actuator to the transfer case, and tapping it and also using the switch to try to engage the center diff lock. Keep trying, like 10 times. Getting it moving is the key, every try might twist it a bit and losen it.

Also check the back of the actuator box o see if the breather line is still connected. If it is, low likelihood it's Corroded inside I suspect. Plus it's beeping so it seems to know what to do.

Thanks a lot for the advice all - I jacked up the truck and loosened the three bolts so I could pull the actuator assembly about 1/8-1/4" away from the differential, once I did I jiggled it a bit then tightened the bolts back up. Started the car up, put it in neutral and tried to activate the lock in H4 while still on the jackstands, but it still just kept blinking and the actuator itself beeps in sync with the blinking. I tried that a few times, along with some more banging on the actuator assembly, and also tried locking it while moving forward and backward in both H4 and L4 but couldn't get it to engage.

Any other tips on getting it working? Can I remove the three actuator bolts completely and pull the assembly off to try manually moving the plunger or rods or whatever is in there?

Having similar problem on my 08 sr5. 4hi not engaging. Both center diff lights and 4wd lights blinking. Can the ADD ( front actuator ) be tapped without dropping the front diff? Has anyone done this?

What a pain. I am paranoid about this so I try to go offroad or on snowy mountain roads and use it every so often. $2,500 is an expensive fix. Does it just freeze up from lack of use or also maybe because of humid or corrosive (Florida, for example) environments?

it doesn't work like that. those rods are pinned inside the t-case. to remove the actuator you have to drop the t-case, and disassemble it, so you can access the pins.

I would continue with what you're doing until it breaks free.

but, how often do you think you'll need to lock it?

I think most who had success by losening the 3 bolts, had left them slighlty loose and tapped the actuator and also turned the switch to engage quite a few times.

Don't just losen and tighten them back up. The rods and gears are frozen in place or have too much tension on them all bolted down, so you are trying to put some slack into the equation to wiggle things lose again.

Check the breather hose on the back, if it's all the way off or split or very loose, thee may be gunk inside too.

Front ADD can to loosened without dropping diff?

Despite my desire to start a new thread... i'll bump this one.

07 V8 AWD

My center dif lock gets used often, and some might say it gets used hard during offroad adventures.
Yesterday I was towing a truck out and started to get stuck, so I tried to engage the CDL and it wouldn't go. It went into 4L great, but wouldn't lock the center diff.

I haven't jacked with it much since then, but all my searching ends up with people who DON'T use their Center Diff Lock.... I use mine once a month on offroad trips.

My truck has seen its fair share of mud and muddy water, what are the chances i've gummed up the actuator housing with muck?

have you tried engaging since? I know mine now goes in easily since i had it repaired. But when i partially engaged...that sucked for 340 miles home.

Just when I did it yesterday. Last offroading trip was about 20 days ago and resulted in this...

When you repaired yours did you did the (3) bolt method or somethig else.

It shouldn't exactly be possibly since the actuator is sealed... but I do recall @jdigitty saying his was full of mud from a similar endeavor so it could be possible?