4HI/4LO Engages on dash but no power to front

Ran into a fun one while I was 2 hours into a trail. 4HI/4LO engages without a fuss, from the perspective of the dashlights, but the front wheels aren't getting power. Low gear still works. No warning lights, no fault codes, 4WD lights stay on as per normal op. Wasn't able to check if the shaft from the case to the front diff was spinning but I'll check now that I'm back home.

Does my logic make sense: if the front drive shaft is not spinning, I'll start with the transfer case actuator. If the front drive shaft is spinning, I'll start with the front diff actuator. Reason why I'm beginning focus on the actuators vs other mechanical possibilities is I do a lot of water crossings due to living and wheeling in a swamp.

And I guess while I'm in there I may as well solder the connections. How can I improve protection from ingress water, silicone around it?

 

Your logic makes sense. If the truck is parked and front driveshaft spins freely, then the transfer case didn’t change modes like it was supposed to. If it doesn’t spin freely, then the ADD never engaged.

I’m a bit stumped how this could be happening with no warning lights. There are limit switches that keep the computer and correspondingly the dash knowing exactly where each item is so that it knows when something is wrong and can give error messages or blink lights appropriately. It’s odd that you’re having this problem with no warnings or anything whatsoever.

I don’t intend to insult your intelligence, but just to make sure, this is not a front open diff problem where you simply lifted a tire and it spun freely, right? I’d imagine not but have to ask.

 

I thought it was very strange too that there's no warnings or indicators. Also forgot to add to the tshoot list checking the relay first.

Intelligence definitely not insulted Valid point on the scenario being confused with normal open diff behaviour. Unfortunately I'm very certain the front isn't getting power.

Appreciate the input hopefully will get this dealt with tomorrow.

 

Theory of operations in a 2nd gen as follows (not sure how much the 3rd gen differs)

When you go from 2H to 4H the 4wd ECU first shifts the transfer case into 4wd, after it sees the limit switches and 4wd Detection Switch on the Transfer Case Actuator in the correct positions it then locks the Front Axle (ADD), once the ECU sees the limit switches and Detection Switch on the ADD in the correct positions it sees the shift as complete and turns on the 4wd indicator.

 

Yep, 3rd gen is the same process. I’m having trouble envisioning how it’s lighting the dash light and not detecting problems. Probably pretty simple to narrow down the problem once actually under it checking what actuated properly and what didn’t. Lots of guesswork until eyes are on it.

 

Yeah hard to diag when we're getting lights on the dash as if the circuit completed. OP, best bet would be to jack up the front, put it in 4hi and see what happens when you rotate the front drive shaft. Go from there

 

If you're right and you get no power with solid 4wd and 4LO lights the most likely scenario I would think is something mechanical is broken.

If the truck is on the ground parked and either the transfer case *or* ADD has shifted you won't be able to rotate the front driveshaft by hand so you can't narrow it down. You'll need to put the whole truck safely on jack stands while in 4wd to diagnose.

 

Are you the first owner? I ask because, if the previous owner had made the 2LOW Mod, that is exactly how the truck would perform with the 2LOW Mod engaged.

 

There's a sequence for that though, no? A quick glance at the 4wd ecu would give us an answer though.

 

Ohhh I didn't catch this, OP, is the truck only missing front drive in 4LO and not 4HI??? I assumed it was both by the thread title.

 

If this is the '23 in your profile, this is a warranty issue. Messing with a brand new truck like you're talking about is gonna cost you more in the long run...

 

Oh and on another note, an answer to your last question.....best way to protect the 4wd system from water? Delete all the electronics

 

It's both

 

Okay, that's what I was assuming, definitely not a 2LO mod thing.

 

Yes there is a sequence to using it, but it acts just like described. It’s called a 2Lo mod but it also gives you 2Hi when you select 4WD Hi if the button is pushed.

 

You can be in 4X4, but if the hubs didn't lock you aren't getting power to the wheels. That is normally what I'd be looking at.

 

Alright, made some progress.
- Passenger side CV had come out enough to ground the axle splines up to where C clip sits. Splines on diff side were fine. I cleaned the inside, didn't notice any debris and replaced the seal and CV with OEM.
- ADD was clean and functioning as expected (as folks had rightly suggested). I soldered the connections while I had it out and added sealant around the perimeter of the mating surface.
- Diff oil was contaminated with dirty water. Flushed it with 10L of gear oil. Drove it around in circles in a parking lot like a lunatic. Flushed and re-filled. More circles. Flushed and re-filled with the expensive Toyota gear oil.
- 4WD confirmed working on stands. Engages/disengages fine on stands and on the road.

Thought all was well but now there's a noticeable grinding noise when in 4WD. Increases with wheel speed, most noticeable past 25MPH. Sounds similar to a rotor/pad rub when a vehicles been sitting for a while. Louder when accelerating or decelerating (coasting). Only happens in 4WD, 2WD is fine and dandy. Basically the opposite of needle bearing symptoms where it's making the noise in 4WD and not in 2WD.

I did notice the driver side CV had more play than the passenger side but it's only about 1/2". I'm planning on pulling that axle anyway to inspect that side of the diff. Probably should've done that to begin with. Any other pointers?

 

You can check that, but sounds like you're going to need to pull the whole front diff and disassemble it to find your problem. CV splines don't typically wipe themselves off.

 

Yeah I was afraid of that.. pulling the other axle was more of a hail mary lol. Appreciate the input.