4hi error

Do you hear the front ADD actuator engage?

 

I did not. Though I wasn’t listening for it. My understanding is that it doesn’t engage until the TC has engaged. Imagine there is a limit switch that confirms the shift then sends signal to ADD.

 

I beleive that is correct, that is why I am thinking that your's is engaging the TC, then tries the ADD, but since the ADD doesn't engage or even respond you hear the second clunk pulling it back out to 2WD. The fact that it is so quick, makes me wonder if the truck even sees the ADD.

One thing to note, there are 4 positions in the TC, 2HI, 4HI, 4LO, and Neutral just like any normal TC. When I got my TC stuck in 4LO I could only ever get it to N, or 4LO. So I think the TC goes 2HI -> 4HI -> N -> 4LO. So from 2HI -> 4HI you don't have to go through N, but from 4HI to 4LO you go through N which is the reason for stopping the truck. Now anyone that knows better can correct me if I am wrong. I beleive my 2000 Tacoma was the same way, however, it had a manual TC lever with the ADD.

 

I will check and see if that could be happening. Very good point.

 

Have been diagnosing a failure to shift into 4wd. Followed the above. Heard the TC actuator motor whir, stop, then reverse. No sound whatsoever from ADD. took to shop this morning and they said there is error code P17ac- Transfer case limit switch. Will pick up tomorrow and get estimate of what is needed and cost.

But I am assuming the TC actuator is not fully engaging or the limit switch is bad. Also assuming that the ADD does not try to engage until the transfer case has completed? And this is why I hear no sound fro the front?

 

The only reference to a Toyota P17AC is for the Tacoma. Maybe it's the same process for the Tundra. http://www.ttguide.net/transfer_shift_motor_limit_switch_circuit_p17ac_-1485.html

 

So the verdict is actuator motor replacement. Shop quoted $1600, with $1400 of that being the part from Toyota.

Going to try to find one used I guess.

 

Any details of specific cause? Is it just normal wear and tear?

 

Do t know at this point. I am still assuming that the root cause was that the previous owner didnt engage 4wd very often, if ever. So I am thinking the limit switch inside is either gummed up or rusted and not working. fortunately/ unfortunately it seems the 2014+ with the BW does not have as many issues as the previous gen.
The though part is that there is not as much info or videos out there on disassembly.

will update as I get in there and see what is going on. I may try to pull the existing one and see if I can fix it prior to ordering one, but since this is my DD, I worry about having it disabled.

 

Thanks @SeminoleATL

 

Picked up a used transfer case motor. Found one for a great price off a wrecked truck with only 14k on the clock!

little tricky getting it installed as I didn’t make note of the position of the fork positioning shaft. Took a little trial and error but seems to be working now.

I am going to do a short write up showing the insides of the old one. I think in the end all mine needed was just the cap with the sensors replaced which would have been 5 minutes

 

Pictures would be great since most I could find online were for 1st Gen Tundras.

 

Here are some pics showing various stages of disassembly. I will create a separate post explaining what I learned.

 

Thanks for an excellent thread from problem discovery to fully successful repair.

I don't even have 4WD, and I enjoyed reading about your resourcefulness. This thread is going to be a huge help and encouragement to anyone with Gen 3 TC actuator problems.

 

In the second video the guy says to turn on the center diff after it was in 4WD. How do you have control of only the center diff? I miss the center diff button in my LandCruiser and have asked about it for the Tundra in the past but never got definitive info.

 

So as always, there’s a bit more to the story. As reported, I changed out the switch and the motor. I actually left the original housing so as to not deal with resealing. after installation I got 4hi no problem, but no 4lo. Last night decided to try to disconnect the battery for a bit based on another thread with 4lo errors. After reconnecting the battery, I was able to achieve 4lo!!

Annnd then, it was stuck in 4lo. Each time I tried to get to 4hi, the entire system would stay in neutral if i tried to put in park while the engine was running, I got a grinding sound, and promptly stopped. Next step I tried was to disconnect the 3 wires from the actuator and let the truck throw error code of flashing 4hi and 4lo. I then disconnected the battery for about 15 minutes and reconnected everything. Once doing this, I was able to get the TC to move back to 4hi, though it still took me turning the switch while in neutral, shifting to D and back to N. Another time the shift didn’t happen until I flipped the switch straight from 4lo to 2wd.

after this I was able to rep East the process a couple times and able to engage all 3 modes, though still doesn’t seem to be a smooth as it should.

1 question, the TC makes a pretty good thunk sound coming in and out of 4lo. How normal is this on the tundra? I remember my 200 series Land Cruiser was louder engaging than most of my other trucks.

 

So in most TLC's they are "All-Wheel-Drive (AWD)" not "Four-Wheel-Drive (4WD)" like the Tundra. Basically the T-case in the TLC acts more like a differential to allow the front and rear to operate a various rotations compared to the other axles giving you the ability to rotate all 4 wheels at different rotational speed. On pavement this is necessary to avoide axle wrap. In the Tundra, it is a traditional T-Case that when not engaged, send 100% of the engine power to the rear axle. When engaged in 4HI it is now split, then 4LO drops the gear ratio between the transmission and the drive axles.

Now, in your TLC, you had a "Center Diff Lock" button that would transform your AWD to 4WD locking the T-Case similar to lockers in a differential. This would make the TLC able to use the functions of a traditional 4WD similar to the Tundra in 4HI. I believe, they also had a 4LO in some TLC's. Also in the TLC's is usually diff locker for the rear axle as well. This was only in the AWD versions, not sure the years.

In a Tundra, the system is Part-time 4WD, and only engages the front drive axle when shifted into 4HI then 4LO. Also in this process is the ADD (Automatic Disconnecting Differential) that locks the front axle together in one piece, this replaced locking the hubs from the old days. Unfortunately, there is no "Locking" differential from the factory for the Tundra, even on the TRD models.

In the 2nd - 3rd gen Tundra, there is a knob just to the right of the steering column below the radio just left of the climate controls that performs the controls of the T-Case. Now this isn't a "Manual" control like in old 4WD's that had a stick (lever) on the floor next to the gear shift, it is an electronic switch. When switched from 2WD to 4HI it tells the computer to start the process of putting the front drive axle into use. It starts with the T-Case into split power and then engages the ADD to lock the front axle together. This is what happens while the 4HI light blinks. Now 4LO is a different story. Since this is a different gearing, you have to stop and not move while the truck engages the lower gear ratio.

 

Mine would continue to flash "4HI" even after I moved the knob to 2WD.
I found that moving the knob from 4HI to 2WD and then slightly accelerating resolves this issue...Everytime.
Anyone else have a quirk with their 4WD?

 

The simple answer is that a center diff is only for vehicles with full time 4wd. If you didn’t have this, you essentially still have an open system similar to a 2wd with open diff.
For instance, if I take my wife’s AWF Highlander and put front tires on pavement and back tires on mud (with traction control off), all the power will go to the rear. If I push the center diff button, 50% will go to the front, hopefully pulling the rear out of the mud.

Sounds like a good example to make a video of

 

Yeah mine does that from 4HI to 2HI, it's the ADD disconnecting and needs to rotate the axle to trigger the sensor confirming the ADD separated the front axles.

 

I have been having the same issue about not going into 4lo or when it did it wouldn’t go back to 4hi. I did the battery disconnect on the trail and it worked, but just got back from Death Valley and I couldn’t use 4lo at all this time. It wouldn’t make that normal clunk at all this time around. I got a new transfer case shift actuator on the way to replace it. Hopefully it fixes it. Has yours been working fine still after the battery disconnect or is it back to being faulty again? And if it is working do you think you fixed it by replacing the motor and switch? Thanks.

 

@Jimes I’ve had the same issue, it doesn’t want to go into 4lo and when it does it doesn’t want to get out of it. The trick that has been working for me so far is, the second I turn the knob from 4hi to 4lo I release my foot from the brake. It has worked every time, when that fails I guess I’ll have to pay the $140 for Toyota just to look at the problem. I use 4wd every single month like the manual says and it doesn’t prevent problems, oh well I’ll update this thread too.

 

Exceptional thread!!!!!! Thanks

 

Yes! A lot ask questions. Then if they fix the issue, abandon the thread. Thanks for sharing with pics.

 

When mine doesn’t want to go back to 4hi I just put the knob on 4hi, turn off the truck, put in park, turn it on and now it’s back in 4hi. No need to disconnect battery. But now I don’t even get the initial clunk when going from 4hi to 4lo. When I get the part and replace it I’ll test it out and see what happens.

 

I learned alot from this thread.

fantastic stuff.

 

So after messing with my actuator I figured it out. I took apart the black can over that piece with all the copper in it(sorry don’t know the name). Took off the cover over the gear inside that turns the transfer case(the part with the wires).

what you find inside is this.



So my truck got stuck in 4lo last night after playing with the little gear inside by turning the green piece. What I found to fix my entire system was to rotate the green piece clockwise with a finger on the end of the green piece to turn the gear clockwise until the gear wouldn’t spin any longer and the green piece tries to back itself out. Once the gear inside is at that point stop, turn the green piece counter clockwise until it sits in all the way. At this point your good put everything back on. You need to hold the gear with a set of needle nose pliers or hand cause when you put the black can on which has two large magnets inside the green piece will try to back out into the can, but if you hold the gear down and in place the green piece will not move and the can will go on without any issues. Screw that back on and put the gear cover (the piece with the wires) back on and screw it in and plug in the three plugs. Make sure you are in 4lo when doing this cause that’s what I was in and basically what’s happening is the gear is too far away from the point of it turning the transfer case. This is where the pin should be before you put the cover back on the gear.
And for reference I went thru each drive to see where the pin was at on the gear after I adjusted the gear in order for 4lo to disengage. Started at 2WD and worked thru all of them.


4HI


I can’t say how long this will work since I just figured this out and will have to test it after I drive for a while to see if everything remains stable. But I did cycle thru 2wd, 4hi, 4lo and back to 4hi and 2wd several times and was flawless every time. What I think is happening is when we go on washboard roads it slowly turns the green piece which turns the gear a little further away from where the pin/gear needs to be at to work properly. My guess. But at least mine works again and it was a free fix. Be careful not to damage the little black O-ring if the gear comes out with the cover with the wires on it. Last, but not least there is a black plastic split collar on the gear shaft that goes into a specific slot on the shift actuator body that has to line up in order for the gear to sit in body properly. Hope this helps someone. Just be careful and take your time. Easy fix though. DO THIS AT YOUR OWN RISK. I am just sharing what I found to fix my system this may not fix yours since other things can go wrong in the system itself. You do not need to remove the entire shift actuator to do this.

 

Out of curiosity, is the breather tube on the top of the transfer case still intact? I know a few members who experienced similar tc motor issues after the breather tube separated from the transfer case. This led to more moisture getting directly into the area that houses the motor leading to rusting and faulty actuation. May prevent possible future issues.

 

This is happening to me, too. My issue is that my 4Hi/4Lo lights flash simultaneously when I am in 4wd. However, it only happens when I am about an hour into being in 4wd and then the lights goes off by itself--I have even been able to shift from 4lo to 4hi when the lights are flashing. Mechanically, everything seems to be working. I am just not sure what the actual issue is yet. The dealership couldn't diagnose the issue.

Did replacing the TC motor permanently fix the issue?

 

My 2016 truck 4hi and 4lo indicator lights are blinking try to switch the control knob back and forth but still blinking try yo disconnect battery for a few hours to reset the truck computer but no luck did a scan and got a code P17AC, my question is if I have to replace the transfer case motor switch do I need to need to remove the whole TC or I could just unbolt it from the TC and replace this thanks in advance. what further testing should I do?