Another 4x4 probem... (System won't shift into 4Lo)

Hey guys,

I have yet to find a thread anywhere that addresses this same exact problem. The dealer wants $105 just to look at it so was hoping if at all possible to avoid that route.

The electronic system has always been somewhat temperamental; however, it has finally stopped shifting into 4Lo this winter. The truck shifts into 4hi and all four tires recieve power, but the 4wd light on the vehicles dash flashes. It refuses to shift into 4Lo. When selected the 4lo light comes on and the beeping sound begins with the 4wd light flashing.

When I shift into 4hi I can hear the transfer case shifting along with the ADD actuating on the front axle. So i dont believe its the ADD? Would this be an issue specific with the transfer case? Is there some type of actuator on the 4Lo system not working? Or is it because the 4hi light flashes so the vehicle doesnt believed its engaged in 4Hi and therefore will not allow it into 4Lo?

Thanks for any wisdom or help! (and possibly saving me some cash)

 

Could be a fuse? Did you check them?

 

Have you tried stopping, then shifting to Neutral between 4HI and 4LO? If it still doesnt shift, what about driving a short distance in reverse or forward, then back to neutral. I didn't think you were supposed to go to 4LO on the fly. Good Luck!

Also, welcome to Tacoma World!

 

sub'd I've got a similar problem good luck!!

 

4lo is 5mph and under, which is pretty much stopped.
With the truck in 4hi, wheels chocked, parking brake on, have soneone shift into 4lo with you listening underneath. Find the manual/schematic to the xfer case and meter the leads/motor.
Don't lie perpendicular to the tires. No partially flattened TW members are allowed on here

 

This, mine does the same thing the op is talking about when moving and not in neutal

 

Doesn't the manual say you have to be in neutral to shift to 4 lo?

 

sounds like the OP has been shifting into 4 LO for quite some time if it just recently stopped working... So I'm assuming he knows how to do that.

 

I believe so, now that I come to think of it I have never been able to engage 4lo without being in neutral.
But
i have no idea why it would just stop shifting onto 4lo, could be a fuse/bad connections?

 

It's recommended to be at a complete stop and tranny must be in neutral in order to shift from H4 to L4. The Toyota repair manual states three suspect areas if shifting from H4 to L4 is impossible.

The number indicate the ranked order of probability of each of the possible causes. Check each part in order. Replace the applicable parts as necessary.

1. Four wheel drive control switch
2. Wire harness
3. Four wheel drive control ECU

Beyond that, and digging deeper it could be the actuator fork (an internal part of the transfer motor connected to the transfer case).

 

What about the actuator?

 

Yea I checked all the fuses. ... the switch still works for 4hi for whatever reason.

 

yes

Assume nothing in TW.

That said I assume operator error based on the beep. The truck only beeps if you are doing it wrong. If he was doing it right and it wouldn't engage I'm 99.9% sure it would just blink.

 

Yea checking the leads is not a bad idea if i can find the schematic... Which way is perpendicular again??? haha

 

I'm 99.9% sure im doing it right. I've owned the truck for 5 years now. Never had a problem with 4Lo before....

The reason i believe that it bleeps is because even when its engaged in 4hi the light still blinks for whatever reason. The truck is basically telling me it is not engaged in 4hi even though i know it is as i have jacked up the entire truck and all 4 wheels recieve power and you can hear the actuactor on the front axle and the transfer case activate when you switch, but for whatever reason the light still blinks. Im guessing since the truck is telling me i'm "not" in 4hi (with the blinking light) that it will not let me proceed to 4lo, as that is the correct sequence.

 

Based on THIS (italicized) quote, I'm not convinced your truck's going into 4wd - even 4HI at all - despite your statement that "all four tires receive power."

The dash switch didn't fail, or it wouldn't even be "trying" to go into 4hi or 4lo.

So that pretty much leaves the failure as either the actuator on the front differential or the actuator on the transfer case that has failed, or the 4WD control unit board.

How mechanically apt are you? You can download the toyota Factory Service Manual sections from toyotaowners.com and it will give you the diagnostics to perform. But if it's in the front diff, you'll need to lower the front diff (you don't need to completely disconnect the front CV axles and remove it) in order to gain access to the front actuator. The access to the actuator on the transfer case is a little easier IIRC. Not sure where the control unit is located or how easy the access is.

In any case, the actuator (on either the front diff or the transfer case) is like a $450 part.

I replace my front diff actuator in a saturday morning, but I'd already had the practice of completely dropping and removing the front diff (twice!) before I did it. If I had to do it the first time, it would take me considerably longer.

Bottom line: It's quite likely you're either gonna have to burn a long Saturday getting your hands dirty (and still be out-of-pocket quite a bit on parts expense!) or pay the dealer (or another mechanic you trust) to get it fixed.

 

OK, based on that updated info - there's a position sensor in both actuators. This reports back to the 4wd control unit the position of the actuator and that it was successfully engaged. Based on your updated description - that would seem to be a likely culprit. You might even be able to disassemble the offending actuator and clean the contacts on the position sensor. That would be considerably cheaper than replacing the actuator. My front diff actuator kept physically jamming and would not move when power was applied to it.

 

I think you are right. This is gonna be one big process of elimination which is what i was hoping to avoid. Hoping someone would have the quick n easy way out. I talked to the service manager at the dealer and he had nothing to offer since the vehicle does go into 4hi.

I'm wondering if the transfer motor or the ADD is not activating all the way even though i recieve power to all 4 wheels, which would warrant the blinking light and therefore not allow me to move into 4Lo. (hopefully not that transfer motor though $$$$$)

 

^ This is correct, and based on the information about the flashing (which I overlooked before I posted first) it's my guess where the problem is too. If the position sensor is bad, while mechanically shifting into H4, the 4WD ECU is not going to know that, thus the flashing light.

Here is the diagram of the system.



Don't know how much the sensors cost but you could take a gamble and swap it out. I found a diagram of where it is.



This shit is all academic for me and I've never actually wrenched on a Tacoma xfer case, I'm just trying to be helpful providing what tech doc I have so... take it for what its worth...

 

Awesome thanks for the info! If i had to guess anything I'd put my money on these sensors. I'll try cleaning the contacts or replace them before i take it to the shop.

Also, when i engage the truck in 4hi the only way to get the truck back into 2hi is too turn the truck off and switch to 2hi and turn the truck back on which will disengage the 4wheel drive, not sure if this could be related to these sensors as well