5-speed A750 trans won't shift in to 5th gear. (7 Viewers)

[MongooseGA]

Looking to see if anyone else has experienced this, as I couldn't find much for what's going on.

2005 LX470, 345-350k miles. Trans has been perfect as long as I've owned the truck, nary a hiccup ever. I last drove the truck on Saturday this past weekend, all is great. Today, the ABS/VSC/TRAC lights came on the dash, and the transmission will no longer shift in to 5th gear. I did a key cycle and the idiot lights are now gone, didn't come back in about 50 miles of driving home. But, trans still won't shift in to 5th. All other gears, reverse included, are just fine. What's interesting is that I never got a code from the transmission. Nothing came up on my SG while the lights were on the dash, and still nothing since they've gone away.

I did a little research, and Toyota suggests a valve body issue in the FSM. Looking around at part prices and what it takes to replace, I'd say it's totally realistic I can do it myself. But before I order a new valve body with solenoids, I wonder if there's a way for me to test anything. Can I manually override the automatic shifting to determine if the issue is mechanical or electric? Can the solenoids alone be replaced, without the full valve body?

I've disconnected the battery as the first, easiest way to reset any computer issues. Will test this shortly.







TL;DR: It was the main ECM located behind the glove box.

 

[MongooseGA]

Confirming, battery disconnect did nothing. I will likely try to do a top off of the trans fluid next to rule that out, as a lot of issues I've found in searching stemmed from low fluid.

Beyond... I'm good with swapping the VB. Hopefully the rest of the trans is fine.

 

[excessive]

have you read the codes that have come up?

 

[MongooseGA]

There have been no codes.

 

[Zuberg]

When I read your post my first thought was "wonder if the fluid is at the proper fill height". Outside of that i don't know.

Valve body swap on these trans is pretty easy if it comes to that.

 

[MongooseGA]

Resolved to do a drain and fill tomorrow afternoon. Would be a fantastic solution if it works and a nice enough way for the truck to communicate with me.

 

[newbielx470]

Anecdotally, this kind of issue could also have been caused by driving in pouring drain, and water got in somewhere under the truck. If that was the case, then it has nothing to do with the transmission. The truck's disallowing the 5th gear is actually a self-protection mode. It may work again after a few days of completely drying.

 

[MongooseGA]

Anecdotally, this kind of issue could also have been caused by driving in pouring drain, and water got in somewhere under the truck. If that was the case, then it has nothing to do with the transmission. The truck's disallowing the 5th gear is actually a self-protection mode. It may work again after a few days of completely drying.

I did wonder about something like this. However, it's been gorgeous here for a week. Not a drop of rain since last Friday in the outer bands of Helene.

 

[LJE]

Is there anyway to run with techstream (or something else) plugged in to see if the vehicle computer is telling the transmission to shift into 5th? That would ruleout some sort of lock-out going out.

I would expect that you'd get a code in that situation - but then again, I'd also expect you'd get a code if it's telling it to shift into 5th but it won't, so definitely a little odd.

 

[shevy77]

Resolved to do a drain and fill tomorrow afternoon. Would be a fantastic solution if it works and a nice enough way for the truck to communicate with me.

Be sure to check the level with the updated specs from TSB-0129-08. Should check with temp between 97F and 115F. The FSM hard copies start the low end of the range at 115F. This will result in more fluid being retained when checking level.

 

[2001LC]

I'd first make sure coolant system, working as it should. With system topped (no air) ECT reaching at least 184F.
Second, I'd do a full 12 qt A/T fluid flush. I set level, A/T fluid #1 at 100F (97F-115f) . I use Mobil full synthetic or Toyota WS. (Note: Mobil is not the same as Mobil 1) Drain and fills, can be problematic. In that over the years, who knows what has been added.

 

[MongooseGA]

Did a drain and fill with Toyota WS ATF today. Fluid coming out was dark but not shimmery or burned. I'd say totally fine for the mileage.

Net results: still no fifth gear. Every other gear is perfect, super smooth, upshifts and manually down shifts just great. It's a perfect transmission in all aspect, except it just doesn't shift in to 5th gear.

ABS/TRAC/VSC OFF came on again once today. Another key cycle cleared it and it didn't return in my few miles of driving around. No codes being thrown for anything.




I started writing this post about an hour ago but have since had a phone call with John from IPT Transmission in NJ. They're the ones with videos about replacing valve bodies and stuff on these A750 units.

Long story short, he thinks it's really strange that the car isn't giving any codes, and that A- my SG is missing codes and I should try a second reader (I will tonight) or #2- Shaft speed sensor(s) are being ****y, or #C- It's an actual physical issue inside the transmission that would require rebuild or replacement. They only perform high performance rebuilds in their shop. We'd already established that his high performance stuff wasn't up my alley, so he had no reason to try to sell me a service. He also didn't feel it was likely to be a valve body or solenoid issue.

So, I'll go scan it again.

 

[MongooseGA]

I'd first make sure coolant system, working as it should. With system topped (no air) ECT reaching at least 184F.
Second, I'd do a full 12 qt A/T fluid flush. I set level, A/T fluid #1 at 100F (97F-115f) . I use Mobil full synthetic or Toyota WS. (Note: Mobil is not the same as Mobil 1) Drain and fills, can be problematic. In that over the years, who knows what has been added.

Coolant system is great. Mechanically, the truck is about perfect other than an annoying heat shield rattle I can't find. I monitor water and trans temp full-time and they're always appropriate.

 

[newbielx470]

Another free thing to try Engage/disengage 4Low and Turn on/off the CDL button, try all the combinations. If there is any issue (even without any code) with the 4Low transfer case or traction control, the truck could also enter this no-5th-gear mode.

 

[MongooseGA]

I can do that. They all get used pretty regularly. Last time it was in low and locked and all that was just this Summer.

 

[SteveH]

Some Toyotas won't go into the top gear until the coolant hits a certain temperature (to promote faster engine warmup for emission reasons). Not sure if this is a factor, but should be considered.

 

[saudi]

I live in uk and mine wouldn’t go into 5th did a code check it was knock sensor. What didn’t realise according to to Toyota uk various faults cause the 5th gear not to engage even if they are not associated to gearbox. You then after repair get tech stream to physically clear codes as battery disconnection doesn’t work

 

[MongooseGA]

Drove it around the neighborhood last night engaging low range and the CDL. Both worked fine, just no 5th gear.

Some Toyotas won't go into the top gear until the coolant hits a certain temperature (to promote faster engine warmup for emission reasons). Not sure if this is a factor, but should be considered.

Thanks. Not a factor in this case.

I live in uk and mine wouldn’t go into 5th did a code check it was knock sensor. What didn’t realise according to to Toyota uk various faults cause the 5th gear not to engage even if they are not associated to gearbox. You then after repair get tech stream to physically clear codes as battery disconnection doesn’t work

Well that sure would be nuts.


I called up a local, well regarded gear shop today. They only do manual transmissions but recommended another well regarded trans shop he knows the owner of. I dropped her off this afternoon before flying out tomorrow for the weekend. They expect to have some diagnosis by the end of the week. I took a little comfort in the woman at the front desk telling me, "We rarely get Toyota trans that do need to be rebuilt".

Something else I just noticed on my drive to the shop: I thought I'd felt a little of this the other day, but confirmed the trans is actually short shifting a little bit. Even with ECT PWR on, it will upshift earlier than it normally would under heavier acceleration. Also, the kickdown is not working. Trans will downshift itself as I come to a stop, but jabbing the throttle does not automatically kick down like it should. Idiot lights came back on today, again with no codes. Meh.

 

[OEMGUY0720]

The principle of an automatic transmission is based of how much torque the torque converter receives from the engine through the crankshaft. I think the culprit may be connected to that when the final gear in this case a 5th gear (smaller gear) is not getting enough torque for it to shift to fifth.

If the at fluid has been ruled out, I am thinking of either the torque converter or the valve body may be the culprit (hopefully not the clutch discs/plates). Just my two cents. Nonetheless I am sub’d and curious how and what be the solution for this unique case. All the best!

 

[2001LC]

IDK, that fluid has been ruled out. D&F is ~3 qt. added to who knows what mix of AT fluids. Unless an owner, has been doing D&F personally, from miles one.

Two issue with D&F:

1. Many measure what comes out and adds back same. In 04 up that means the AT fluid, is low.
2. Mixing of different AT fluids.

I've found more than one, AT diagnosed bad. They come to me, I do a proper 12 qt. flush and set level correctly. AT then works as it should.

I see now mentioned after D&F, more noticeable shift issues.
D&F, but no mention of debris in fluid. I don't see mention of filtering the drained AT fluid, checking filter for debris.
I don't see, what ATF #1 temp used, to set level.
I see ECT normal, but no mention of what that temp is.
No mention of checking under radiator cap for air and color. We need to keep in mind, ATF flows through radiator.
I see AT fluid temp monitor while driving, but no mention of what that temp is.
I see no mention of any previous issues or DTC or work performed. It always a good idea to look at history.

I see mentioned "fluid dark" I'd want to see red especially for diagnostics in this case!

It may indeed turn out to be a bad AT. But that is not the norm. I would expect a bad AT, to have shown itself, long before 350K miles. Unless a fluid issue, has been damaging it.