Hi all, obligatory "first post". I've had my 06 V6 4x4 Limited for a year and a half now. It's been great, I love the truck and it's easy to work on. It's not without issues, but I'm fine with that on a 15 year old vehicle and part of the appeal to me is that it's easier to learn on and fix up than a newer car!

Anyway, it has ~110k miles on it now and I've noticed in the past month or so that it's not getting into OD on the highway. Every other weekend I drive approximately 3 hours on Rt95 but lately it's all been in 4th gear at like 3200rpm. I understand this isn't terrible to do, but I'm worried about the cause of this issue. First time I noticed it, I pulled off and restarted the truck, and then OD worked for the rest of the drive. Since then though, no OD. I've searched around but haven't found anything definitive, but here's what I've learned:

• The tranny won't engage OD unless the engine and/or ATF temp sensors register a high enough temperature
• A faulty solenoid could be preventing the OD gear from engaging
• The AT fluid in my 06 is "lifetime" and the transmission is sealed, but possibly low or old fluid could cause this issue
• I don't think it's a "transmission" issue as much as an electrical or fluid issue

So, I'm trying to start with the easy and work to the hardest in troubleshooting. The V6 doesn't have dedicated "4" and "D" shift notches, so it's in the right gear and I'm not accidentally bumping it out of OD. The weather is warm and I'm driving for hours, so it's not a legitimate cold tranny issue. All other gears are working fine, the transmission shifts smoothly, and it doesn't hunt for gears.

First, can anyone tell me if I'm on the right track?!?

Second, can anyone confirm which temp sensor(s) the computer uses to determine when OD can engage? I'm thinking this would be the easiest fix. My engine temp gauge still works so I'm assuming that sensor is fine? I would be able to replace sensors on my own if anyone can share part numbers and a brief writeup.

Can anyone comment on the "lifetime" AT fluid? Would that be an issue at 110k miles? If a tranny fluid swap is known to help this issue, it might be worth taking it to a dealer for that; I don't think I would attempt that work on my own.

Moving on to the solenoids... I'm pretty hazy about the inner workings of a transmission so I'm not gonna pretend to know. Would a sticking solenoid prevent a single gear from engaging like I've described? Is it possible/worth it to check on or replace a solenoid?

I do my own oil changes and installed my lift on my own but I'm no mechanic. I do have access to a shop though so with info and a plan I can do simple repairs.

Any help is appreciated!

Start with changing the transmission fluid, I bet that's the problem. I have 380,000km on my 06' V6 and I've done it twice now (but I tow).

Toyota does say it is lifetime fluid but that's really not the case. If you tow or do any high performance driving, or even live in a hot area like CA or AZ I'd do it every 50k.

first of all, the OD is not related to temperature, the trans should go into OD at the right speed & engine load regardless of if its -10f or 100f. so its not related to temps of the engine or trans/fluid.

the fluid is not lifetime, toyota recommends change at 100k miles or 60k if towed or abused, however, at 110k miles its should still be ok depending on its history. based on the symptoms you describe i dont think a fluid change will fix the OD issue unless its low, sounds like its solenoid/sensor related or possibly shifter/cable adjustment issues. best is to have a mechanic or trans shop look at it & test & diagnose further. also check for any codes that may be strored. but a fluid exchange is due so it cant hurt to try that first.

This contradicts a lot of the info I've been seeing that the computer holds out on using OD until certain temp parameters are met, in an effort to reduce engine strain or reduce emissions or something.

It does sound like new fluid should be at the top of my list though, I didn't realize it has a 100k life. And I'll check for codes, I have a cheap code reader. Thanks!

Yeah it looks like that should be my first change. I'm also going to check for any codes, it's not throwing any check engine or OD lights or anything but maybe there's a code stored. Thanks!

Each gear has an individual solenoid, so yes, a single faulty solenoid can prevent a single gear from engaging. I dont know what the process is to do this on the Aisin unit in your 4runner, but Ive replaced solenoids on a ZF trans on my BMW xDrive wagon . . . some skill and problem solving required, though not an awful job. I too have a lift in my garage, which reduces a significant amount of brain damage.

I would check codes in the TCM, then ECT/TPS sensors, then look at fluid. It sounds like you are going to replace fluid, so might as well see if any of the other items are shot, then go on to the fluid. Maybe check and see if you can drop the valve body that holds the solenoids (or however it is on the Aisin) and if its easy/cheap, give it a go.

I wanted to double down on this. There's 75 mentions of the word "transmission" in the '08 4Runner owners manual (the earliest I had readily available, as far as I know, identical mechanical drivetrain in both V6 & V8, same transmission to both engines anyway).

There's no mention of the transmission being "sealed", lifetime, or non-serviceable.

The exact text is:
We can agree that it is worded here to imply it doesn't need to be changed except under specific circumstances. However, it's not saying it never needs to be changed and/or should not be changed. And as firebirdguy pointed out, there's a service interval listed for transmission fluid in the maintenance guide.

See: Maintenance Schedule - Toyota Canada

I recall reading Toyota removed the dipstick because many vehicles were coming in for service due to overfilled transmissions. Having had a 3.4L 3rd gen with the 4sp, it was notoriously difficult to get the level exactly right while checking it with the dipstick. It's an understandable change to the fill/full port system on the A750x transmissions.

Anyway, almost every transmission thread talks about the sealed/non-serviceable fluid myth. I'd speculate to say the manual's terrible phrasing doesn't help to halt the myth... but it's certainly a service item that should not be ignored.

I'm sure someone's gonna roast this post by throwing down the TSRM's page about the transmission being sealed, haha. I don't have time to root around and find the page, but I'd like to know what the spec there is. It would be a terrible irony if the factory service manual said something that conflicts with Toyota's own service interval website.

Do you have any CEL or codes? I was getting a p2759 for torque converter clutch solenoid, which resulted in it occasionally not being able to shift into overdrive and torque converter never achieving lockup. Transmissions are really out of my wheelhouse, so I took it to shop that diagnosed the issue to be the transmission external wiring harness connector. Apparently this connection on the transmission is really prone to corrosion, so they soldered in a new connection and that fixed it.

Also DriftwoodDaddy is a pretty good username lol. I live in Annapolis and commute to Baltimore for work, so I'll be on the lookout for a fellow old man tan 4runner on the road. If you're interested, theres another guy with a 4th gen in MD and we may go to AOAA or Rausch a few times this spring and summer

Everyone has covered most of the bases on what could be causing your issue...but I must ask what gear is showing/lit up on your instrument cluster when it's not shifting into OD?

This is good info and supports what I've been hearing. Thanks for sharing, I'll bump up "ATF change" to my first order of business!

No CEL, I'll run my cheapo OBD scanner tomorrow to see if it's throwing any codes. It's looking more and more like a job for a transmission shop, either to change the fluid (I don't feel like dealing with that...) or check the connections and try to diagnose the issue.

Thanks for chiming in! I've seen your name all over this forum, cool to find out you're local. I actually commute the opposite way, BalCo to AACo, but in a work truck. If you know a good place to grab some AT tires around here (255/70r18?) let me know! Then maybe I'll be able to tackle Rausch...

curious where you are seeing this info, can you post a link? i live in the midwest & winter temps are regularly in single digits & can be below zero for weeks straight... every single time i drive my 08 4runner it will shift to OD when the speed & engine load call for it, same for previous vehicles ive owned or current ones with OD, they all go into OD when necessary. & most my drives have me hitting 40+mph within minutes & the engine temp gauge has barely moved. OD is not or at least should not be temp related.

I found a lot of references to it while searching through this forum, it seemed to be accepted as accurate. Something about allowing the fluid to warm up enough to attain maximum performance/efficiency. I have no problem being wrong though! But would make sense to me.

That being said!! I think you've actually solved my case. While looking for threads to link for you, I stumbled across your thread asking about "4 vs D" on the shift gate...I think it turns out I'm just a massive idiot and never realized that there are, in fact, 2 individual shift positions there. I'll double check when I get home, but I'm suddenly feeling relieved and embarrassed! I have definitely been using the "4" position recently, I thought that's what I've always done but maybe not.

I'm an idiot. I've been putting it into 4 instead of D. I did not realize it's two individual positions on the shifter! After a year and a half....

Thanks for helping me come to this realization!

Alright everyone, crisis averted. Turns out I am a dummy and never realized that "4" and "D" are individual shift positions... the labels are right beside each other so I had just assumed it was "4 with OD" not "4 and 4 with OD". I feel dumb but am glad there's nothing wrong with my truck!

I'll also still plan on doing an AT fluid replacement at some point, but I need new tires first...

Thanks for all the detailed replies and the good info.