2nd Gen 4WD Issues

Hi All,

Can anybody accurately describe how the 4WD system works in a 2nd gen Taco? I am talking about complete flow of movement from the 4WD selector all the way through to activating the front diff? I am having several issues with the 4WD system, but as of right now, I don't believe I know enough about the system to troubleshoot yet. I already pulled the 4WD actuator from the front diff and soldered the servo to the terminals, done a cont check and all seems to be good. That didn't work now am wondering if the transfer case needs attention. A lot of my questions will be answered if I can get a detailed description of how the system works in general.
Thanks

 

When you request a shift from 2HI to 4HI the 4WD ECU first drives the transfer case actuator to shift the 4WD shift fork to engage the front output. This shift uses a synchro to spin up the chain, front output, front drive shaft, and front ring and pinion to the same speed as the rear output and once matched up completes the shift engaging the front output. Once this shift is completed feedback from the indicators on the transfer case shift rail let the 4WD ECU know this is done. Then the 4WD ECU drives the front ADD actuator into engagement. Once it knows this is complete it lights the 4WD solid.

When you go 4HI to 2HI the ADD is first shifted out of engagement and once this is confirmed complete the transfer case is shifted back to 2WD which disengages the front output.

This is for 3rd gens but may help. https://www.tacomaworld.com/threads/4wd-actuator-troubleshooting-transfer-case-and-add.578262/

There are lots of good troubleshooting threads on the 4WD system. After you do some troubleshooting search around for your specific issue.

 

Alot of good info on the 4wd system in the threads posted here.

 

Description of your issue will help.

 

ok, so there is a separate actuator/mechanism for the transfer case, it doesn't solely rely on the ADD. Is the transfer case and the front differential in the same region? I assume the transfer case is toward the front of the vehicle?

Full description of my issue:

Truck was given to me with:

• 4LO light flashing
• Told the 4WD system is not working

Vehicle is NOT stuck in 4LO and I have tested the 4WD on gravel roads and wet grass--front axle is not getting power.

Since getting the truck, I have done:

• Taken ADD off and soldered the servo terminals to the housing connectors.
• Perform continuity check on the servo. Servo works fine and operates the shift fork
• Tested open circuit voltage on the electrical connector that mates to the ADD----found open circuit voltage to be 0?
• Jacked the front end up and turned the front wheels--front wheels move the driveshaft when turned

What I have not done:

• Looked into ECU, relay, or any other electrical components of the system
• Have not looked into/at transfer case

This is where I am at and probably looking to take it in unless there is clear details on what work/operation it needs next.

Thanks for any comments

 

The transfer case is bolted to the transmission.
The front drive shaft is connected to it.

If the front drive shaft turns in 4WD by turning the front wheels. I’d suspect the Actuator on the Transfer Case.

 

What if you locked the front axle but are still in 2WD? When I pulled the ADD off I may have moved the sleeve such that the front axle was engaged. That will explain why the front driveshaft turns when I turned the front wheel? Based on all the problems/issues with the electronic 4WD system, I don't want to try and fix it only to wait for it to fail again. Other than the FJ transfer case, has anyone tried to turn this 4WD system purely to a manual one? Take the 4WD fork from the transfer case and the front actuator and rig up two linkages to the cab?
Kind of out there I know, but if I am going to muck around with this system I may as well do it so it will last

 

Yes, I think @6 gearT444E has done something like that?
Different switches for the ADD and Transfer Case

https://www.tacomaworld.com/threads...or-diff-actuators.695818/page-2#post-24624748

 

Lightly tap on back of actuator on the transfer case with a hammer. Then pull of the plastic cap and see what is going on. Also can you hear the front ADD engage when shifted in to 4HI?

 

you can use switches to independently control both, then you have no need for the 4x4 ECU. To semi automate things you could install your own relay driven off the 4wd detent switch in the transfer case to energize a DPDT relay coil to engage the ADD.

there was another member on here that also rigged up his own cable setup for the transfer case actuator. While all that sounds grand it’s still a bandaid to the problem which has a very easy solution, a full time axle up front and a manual shifting factory case from the FJ cruiser.

think about how many times you need your 4wd, most people not too many. So when you want it to work it needs to be reliable. Stick with the KISS method. I’ve never seen any threads complaining of a manual shifting transfer case or manual hub setup not working when they didn’t expect it to. I myself believe in advancing technology and using it to our full benefit but if the design is not reliable then there’s no place for it in my life. The electric cases were made purely for the soccer moms and people who are too lazy to get out of their car or shift a lever, sadly that population is around 80% of the market for the auto industry, hence why they continue with the poor design.

 

In addition to tending to the lazy and inept population, it’s also a huge money maker for the vehicle manufacturer. When I see how many threads are created on blinking 4wd lights it sickens me. Imagine how much Tech labor is spent shotgunning the problem, and how many actuators they’ve sold as a result of this crap design. the new ones they sell have just as much of a poor performance as the original actuators. Rube Goldberg would be proud of Toyota on their engineering of this system that’s for sure.

 

To step off my soap box a little and provide some info to try and help, I'd suggest investing in 4 jack stands and a good multimeter and reading through the attached documents. These will pinpoint exactly where your problem is. From my experience, the 4wd ECU and the 4wd switch is almost never the problem, but do not discount any component until proven. The issue may be intermittent as well, so if it works once for you, there is no guarantee it will work again, test and retest multiple times.

 

IMO the worst thing with Toyota's 4WD system is it's inability to set DTC's and display live data, other than that it's a relatively simple system compared to some other manufacturers.

 

this is another issue for sure. It’s not connected via CAN bus to any other systems, so you are stuck in the Stone Age to troubleshoot compared to other manufacturers. Would be nice to have real time monitoring of each feedback signal, it certainly would simplify troubleshooting. Toyota having to create multiple documents for techs to accurately troubleshoot the issues is a testament to this design.

 

People hated the vacuum actuated systems back when they came out.
Then they decided to throw electronic actuators down in the water prone areas.

Even I managed to figure out the vacuum system on our Ford.
Hopefully I never have to “figure out” Toyota’s system.
If I keep it long enough, I bet I will?

 

they were built to break, so unfortunately it’s only a matter of time. The vacuum systems are much easier to diagnose, although they present their own challenges. I chose to go with the fully manual setup on my super duty as well and replaced the stock hubs with a nice set of warns, and haven’t had a lick of troubles

 

good info on here, will look into it all. As a quick and dirty fix so I can get into at least 4H for my snow trip (leaving tomorrow afternoon), can I pull the transfer case actuator off leaving the shift fork exposed so I can engage it if I get stuck? I would obviously cover it up with something the internals aren't exposed. My front wheels are already locked to the axle so would just have to put the transfer case into 4H. Has anyone pulled the transfer case actuator off? Are you able to pull it off without losing transfer case fluid? I saw another post that showed the transfer case with the shift fork exposed, just didn't see info on the process of removing the actuator itself.