5-speed A750 trans won't shift in to 5th gear. (6 Viewers)

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2001LC said:
One thing I do and Toyota Tech training teaches. Is look for why a failure occurred. It's rare to have a defect in a 100 series part, but does happens. But when they happen, usually in first few year/50K miles. For you to have a ECM failure, is unusual.

Can you think of anything, that may have shorted the ECM?
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Who can say? My truck doesn't ever want for anything, but it isn't babied at all either. I've floated it across rivers with water over the hood, slammed it on car-sized boulders, sheared various parts of suspension/running gear off of it, sunk it in GA clay to the point of having to remove interior to clean it, spun all 4 big tires at once with diffs locks, etc. She also lives outside because the garage is full of garage queens. It's well used, and has a habit just fixing issues on her own (sometimes).

Here's something that my Ms and I were discussing the other day: Earlier this year while prepping the truck for CRockies, there was a super annoying issue with the door locks after a rain or a wash (cuz I wash my jambs every time). Driving down the road, the locks would just flick back and forth, very fast, for a while. I replaced the PF door lock actuator motor and the issue has gone away. But, while in CO for CRockies, we noticed that 5th gear was not kicking in while in low-range on the trails. Wasn't a huge concern as we were only doing very low speeds, but it had slipped my mind until now. Driving to and from CO in high range, no issues at all. Totally fine.

So I'm wondering if A- the door locks were any kind of indication of something related and #2: would it be feasible that the trans issue (no 5th) would vary whether in high or low range? Could it all be coincidence?
 
J1000 said:
Awesome work, guys! The ECM was also one of the last things on my list but glad you were able to reproduce the issue and figure it out!
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I am very optimistic that the issue shall be resolved by the end of this week.

But also, I've felt that way once or twice already :rofl:
 
MongooseGA said:
Who can say? My truck doesn't ever want for anything, but it isn't babied at all either. I've floated it across rivers with water over the hood, slammed it on car-sized boulders, sheared various parts of suspension/running gear off of it, sunk it in GA clay to the point of having to remove interior to clean it, spun all 4 big tires at once with diffs locks, etc. She also lives outside because the garage is full of garage queens. It's well used, and has a habit just fixing issues on her own (sometimes).

Here's something that my Ms and I were discussing the other day: Earlier this year while prepping the truck for CRockies, there was a super annoying issue with the door locks after a rain or a wash (cuz I wash my jambs every time). Driving down the road, the locks would just flick back and forth, very fast, for a while. I replaced the PF door lock actuator motor and the issue has gone away. But, while in CO for CRockies, we noticed that 5th gear was not kicking in while in low-range on the trails. Wasn't a huge concern as we were only doing very low speeds, but it had slipped my mind until now. Driving to and from CO in high range, no issues at all. Totally fine.

So I'm wondering if A- the door locks were any kind of indication of something related and #2: would it be feasible that the trans issue (no 5th) would vary whether in high or low range? Could it all be coincidence?
Click to expand...
I don't think it goes into 5th in low range, at least that I can tell.
 
MongooseGA said:
Who can say? My truck doesn't ever want for anything, but it isn't babied at all either. I've floated it across rivers with water over the hood, slammed it on car-sized boulders, sheared various parts of suspension/running gear off of it, sunk it in GA clay to the point of having to remove interior to clean it, spun all 4 big tires at once with diffs locks, etc. She also lives outside because the garage is full of garage queens. It's well used, and has a habit just fixing issues on her own (sometimes).

Here's something that my Ms and I were discussing the other day: Earlier this year while prepping the truck for CRockies, there was a super annoying issue with the door locks after a rain or a wash (cuz I wash my jambs every time). Driving down the road, the locks would just flick back and forth, very fast, for a while. I replaced the PF door lock actuator motor and the issue has gone away. But, while in CO for CRockies, we noticed that 5th gear was not kicking in while in low-range on the trails. Wasn't a huge concern as we were only doing very low speeds, but it had slipped my mind until now. Driving to and from CO in high range, no issues at all. Totally fine.

So I'm wondering if A- the door locks were any kind of indication of something related and #2: would it be feasible that the trans issue (no 5th) would vary whether in high or low range? Could it all be coincidence?
Click to expand...
Water entry into front cabin area:

Water entry into dash, RH & LH junction boxes and their areas which includes computers. Have their root beginning, due to bad windshield install in 98 out of 100 cases. These leaks, have totalled both 100 & 200 series, due to electrical gremlins.
MongooseGA said:
Well... huh.
Click to expand...
What ?
 
2001LC said:
Water entry into front cabin area:

Water entry into dash, RH & LH junction boxes and their areas which includes computers. Have their root beginning, due to bad windshield install in 98 out of 100 cases. These leaks, have totalled both 100 & 200 series, due to electrical gremlins.

What ?
Click to expand...

It's possible there's been some windshield leaking, but short of this issue (and maybe the door locks), there's never been anything to imply that. I'm happy to report there was no water instrusion in to the cab during any water crossings. It's actually pretty impressive. The only reason I can think mud entered the floor of the cab one time was due to the whole truck being in kind of a twisted position, possibly compromising the pressure on the seals.

That latter post was related to 5th gear not being normal in operation in low-range. I've never heard this before, but I've never noticed it myself.
 
I don't know if this is what @2001LC meant or not, but when you said you wash your door jambs, my mind went to water intrusion to the ECM from that?
 
Actual footage
1000005828.jpg
 
J1000 said:
I don't think it goes into 5th in low range, at least that I can tell.
Click to expand...
That is my understanding, too.

OP, given the timing of your using of a system that locks out 5th, your recollection that 5th definitely was locked out at that time, and a short time later 5th being locked out all the time, it probably would warrant a little time looking into how 5th is locked out in 4lo and whether a malfunction in that process is causing your current problem.

Edit: at a minimum I would try going in and out of 4lo a couple times
 
I’m pretty sure overdrive doesn’t work in low range, even in the 4 speed trans.
 
Interesting...I could have sworn I get to use overdrive in low range (4-speed, center diff not locked).
 
Bisho said:
I’m pretty sure overdrive doesn’t work in low range, even in the 4 speed trans.
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I thought I knew this to be correct, but I couldn't remember why I thought that. So I looked. I cannot find anything in any documentation I have for any A343F that indicates the O/D is disabled when the transfer case is in LO position.

The only thing I can find is:

a) cruise control disables O/D (temporarily) if the setpoint speed is higher than vehicle speed, and
b) ECM disables O/D when transmission coolant temperature is below 131°
c) the O/D switch is set to OFF (obviously)

otherwise, it appears it is always available. I don't know why you'd want O/D in LO range, but apparently you get it.
 
Malleus said:
I thought I knew this to be correct, but I couldn't remember why I thought that. So I looked. I cannot find anything in any documentation I have for any A343F that indicates the O/D is disabled when the transfer case is in LO position.

The only thing I can find is:

a) cruise control disables O/D (temporarily) if the setpoint speed is higher than vehicle speed, and
b) ECM disables O/D when transmission coolant temperature is below 131°
c) the O/D switch is set to OFF (obviously)

otherwise, it appears it is always available. I don't know why you'd want O/D in LO range, but apparently you get it.
Click to expand...
I can say that with reduced low range transfer case gears, having a 5th gear or OD is (or would be? ) actually really great, otherwise your engine is screaming between obstacles. You could go to high range, but that's not always ideal.

I'll try it out once my new ECM arrives.
 
...but you have an A750F - I didn't check that.
 
I just tested this in my 07. Only 4 gears in low range. I’m almost positive I only get three in my 2000, but won’t be testing today.
 
I verified no overdrive in low on my 2000, as well.
 
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