4wd System Operation & Help Thread

What a great thread!

My 2007 just threw the dreaded flashing 4wd with the 4L. Before I found this thread, I had replaced the ADD actuator. What a PIA that fourth bolt was!

Anyhow, the error was still displayed. I decided to bring it to the dealer. Debriefed the mechanic on what I did and the results. An hour later the shop called and said they fixed the problem. Mechanic said he had to resync the ADD with the transfer case actuator. I understood what he was telling me because of this thread.

My question is, how does one resync the two actuators? I assume it has something to do with the limit switches in each actuator. I could not see a process to do it. Obvious it can be done. How is it done?

 

I'm curious what dealer charged to syn actuators. Tia

 

I’ll report back once I know. I pick up my truck tomorrow.

 

I would think you could pull the actuator, then supply power to the motor until you get the correct readings for 2WD on the limit switches. Then make sure the truck is in the 2WD, you can do this manual if needed, then reinstall the actuator.

 

Normally I would expect the ECU to do it itself but I suppose if the limit switches land in certain combinations it could get confused.
The actuators can be moved manually with an external power source as @TnShooter said, you would just want the limit switches to be in the proper positions for where the selector switch is.

 

If I understand the schematics, the actuator in the transfer box is the 'master' and I would need to syc the ADD actuator to the transfer box actuator.

What is interesting is the replacement ADD was in the same position as the bad ADD I removed. The ADD died with the truck in 2WD.

Could I have simply pulled the ADD and cycled the ADD using the cab switch? OR would the 4WD module step in a say 'he11 no'?

Seems like the ADD is the tail of the dog (=xfer box), it would do what the dog tells it to do.

oh well, it's fixed before we get dumped on today 12+ inches of snow.

Again, my compliments to the OP and others that added to the thread. So helpful!

whitedog

 

I forgot I owned the FSM for my Tacoma. Look what I found in the schematic section:

 

Still not exactly sure about the re-syncing of the actuators, I only can test a known good.
I still haven't actually had the opportunity to diagnose the 4wd on a Tacoma or Tundra yet (we just don't work on many of them at the shop), I put this thread together using service info, testing on my own truck, various threads here, and help from various members.

The ECU is controlling everything based on inputs from the limit switches and selector switch, it can only infer the position of things based upon the combination of the switches being open or closed.

As far as the full logic behind it's decisions on when to try to move the actuators to the desired positions and when to lock the system out and flash the light when a switch(s) don't agree with the desired position I can't be certain, it would have been nice if Toyota had given us visibility into the system via a scan tool (or at a minimum flash codes) but they didn't.

 

I haven’t found a good explanation of the logic either.
I know there have been multiple reports of 4WD NOT working with the truck On.
But if you turn 4WD on with the truck OFF, it will work.
Again, this isn’t in all cases, it’s just a report I’ve seen multiple times. Not sure the logic in that?

Until you actually scoped the system, I was only guessing at what sequence the events even happened

I believe even Toyota learned something, as the 3rd Gens have diagnostic codes for the 4WD. (11 of them)
At least 3rd Gen trucks have the ability to “point you in the right direction”.

 

I've seen this too but again without having a broken one to put my hands on all I have is theories as well.

Yea, most other mfr's have had built in diagnostics since the late 90's but Toyota for some reason chose not to.

 

Well, Reporting back;

The sync did NOT work. The mechanic called and told me after a few cycles, the lights returned back ‘on’.

Someone asked about what the dealer charged for troubleshooting the 4wd error. My dealer charged a fee of $150.

The truck is back in my possession as the dealer is asking what I want to do. They want to replace the xfer case with a rebuilt unit. I want to measure the voltages myself and make an educated decision, not an ‘quick and easy’ fix. The xfer case actuator is in my sights now and I want to prove that it is still good by taking voltage measurements inside the warm cab, not laying on a concrete cold floor!

Dealer is quoting $2k for the case and $500 labor. eek!

Are the 3rd party xfer case actuators any good? I see several of them on Amazon in the sub $300 price range. They all look the same. Plus it appears the actuator can be replaced by pulling the pinion gear and leaving the actuator fork rod in the xfer case. Unplug and unmount the actuator body and install the new body on the case. Install pinion gear and seal the lid, you’re ready to go. Is it that easy? Can you mix rods and pinion gears like I have seen on youtube videos?

$300 is 1/7 the cost of a rebuilt xfer case. maybe an hour of my time!

Your thoughts?

 

@WhiteDog have you looked at Rock Auto?

I was having issues with the ADD up front. Long story short, it's working again. There are signs of water intrusion though. That and snapping a screw, are motivating me to just replace it.

Rock Auto has what I believe is the OEM ADD for under 200 bucks.

A 1" wobble extension will be your best friend in removing 1 bolt. I wish I had one. Lol

 

Do not replace the transfer case unless they can prove to you beyond a doubt that there is an internal issue preventing the shift forks from moving.

My buddy has the theory that voltage fluctuations during the startup process might be enough to complete the appropriate circuits and satisfy the logic. If one of the limit wiper switches or detection switches has some corrosion or moisture in it, the voltage fluctuations might just be enough to complete the circuit. Thats the only theory Ive heard that makes any sense as to why turning the truck off and on again does anything

 

Larzzz,

Thanks for the heads up. I have determined the new ADD was likely fine.

That fourth bolt is a PIA. I was able to remove it with a mini 1/4" ratchet handle (oal was 2 inches) with a socket. Good thing my Alexa could not hear me, she would likely report me to the Authorities.

I'll check out Rock Auto for the the xfer case actuator.

 

@SR-71A yes, I agree, I have a few days to decide. Weather here is terrible, too difficult to work on my truck underneath. However, I can perform the measurements inside the cab.

Until I measure myself (sorry Toyota, but $2k for a xfer case is ALOT of muulaa), I want to convince myself I need to go to that level. It's not that I don't trust the dealer, but, when I asked about the results of them testing the voltages, I did not get a warm feeling they dug that deep. More like "Oh let's replace the xfer case." Dealers make money on throughput, I guess.

When I asked if the xfer box imploded, (broken pieces jamming the mechanism), their canned response was to pay them to remove and open up the case to inspect.

Sorry, not at this time.

 

Probably the reason they want to replace the transfer case is because the Toyota procedure to change the actuator is to remove and disassemble the transfer case, it's easier for them to just replace it.
The actuator can be changed without removing and disassembling the transfer case but it has to be disassembled and it may take a few tries to get the timing correct when it's reinstalled.

 

I am doubting that theory, what I believe to be more the case is that there is a power up pulse that allows some time delay for the expected limits for the given command. After this times out, any further command is locked out until the power up pulse is initiated again.

 

I’m going to take a 99% educated guess that nothing inside your transfer case is at fault. You can confirm this by removing the actuator and manually shifting into 4lo to check for binding. Dealers are like doctors, that’s why you are a customer and not a patient. They will sell you the most expensive option if you are naive enough to pay.

 

Thanks,

I plan on taking voltage measurements at the 4wd ecu box behind the glovebox. Currently my truck (2007 access cab) is in 2wd and not showing any errors. I replaced the ADD and the dealer sync it once.

Interesting to see the voltages in 2WD, 4WH, 4WD low.

If the measurements point to the tc actuator, I have one on order due 2/15. My plan is to remove the existing tc actuator by removing the pinion gear and removing the body of the tc actuator. I will leave the fork shift rod in the tc.

Question: Has anyone found a low cost solution for both of the two limit switches in the tc actuator body ? I saw one post the non-keyed switch can be found for <$30. How about the keyed limit switch?

whitedog

 

They may be the same as a standard reverse switch, but then you'd need to source the connectors. These are also very easy to test, remove from actuator and push in the detent ball, ohms should go to zero. With detent ball retracted, should read open circuit.

8422212010
8422235121