5-speed A750 trans won't shift in to 5th gear.

[LJE]

OK lemme get my head straight here. The results at either end are effectively the same thing? Would not measuring at the ECM side be indicative of the solenoid, and measuring at trans connector be indicative of ECM? I'm seeing it as reading what signal is getting through to the other side. Both bad readings would only bad wiring I'd think. Am I off?

Ahhhh I see where the disconnect is at here.

When you're measuring at the transmission connector, you are measuring the *transmission* side of that connector, not the ECM/engine harness side. So you're still measuring the solenoid, but now via the transmission wiring harness.

When you measure *at* the ECM connector, you should be measuring the same thing - just with the engine wiring harness between your meter and the transmission wiring harness + solenoid. If you measure there first and get good readings, you know the whole chain is good. If you don't get good readings, that's when you look at which of the two links it is - either the transmission wiring harness, or the engine wiring harness.


Does that make sense? If not, I can totes draw it out on paper - this is something much easier to explain with pictures rather than words, haha.

 

[MongooseGA]

Ahhhh I see where the disconnect is at here.

When you're measuring at the transmission connector, you are measuring the *transmission* side of that connector, not the ECM/engine harness side. So you're still measuring the solenoid, but now via the transmission wiring harness.

When you measure *at* the ECM connector, you should be measuring the same thing - just with the engine wiring harness between your meter and the transmission wiring harness + solenoid. If you measure there first and get good readings, you know the whole chain is good. If you don't get good readings, that's when you look at which of the two links it is - either the transmission wiring harness, or the engine wiring harness.


Does that make sense? If not, I can totes draw it out on paper - this is something much easier to explain with pictures rather than words, haha.

OK so here's the trans harness. Am I correct to assume that the connectors in yellow would be the transmission side of this equation? Red being the engine/ ecu side.

 

[LJE]

View attachment 3760755


OK so here's the trans harness. Am I correct to assume that the connectors in yellow would be the transmission side of this equation? Red being the engine/ ecu side.

Yessir, that would be correct!

 

[2001LC]

As you work on wiring. Keep in mind, the wire housing block(s) with corrosion inside. Corrosion inside means, either the seal failed or it was not fully seat making a good seal. The block on LH (driver side) has a very special locking mechanism. Which indicates Toyota engineers were very concerned with that block prehas with moisture. For some reason in that one, more than the others.

I would think your issue, began at a time one or more of these were disconnected and then not fully seated when reconnected. Perhaps making a good enough contact/continuity, no faults at the time. Then over time, moisture made its way into housing block.

There are only a few services, where one or more would have been disconnected. One bing (but not needed), is starter R&R. Others are engine or transmission R&R. Even could have been diagnostics work in the pasted. Knowing a vehicles service history and carfax history, has value in diagnostic.

I'll note: I did see one 01LX, that had history of electrical gremlins. It's the one I pictured AHC wire harness block corrosion. It's history showed various electronic issues, starting while still under warranty period. We don't know why, these wire housing blocks seals were failing. Was it a freak factory issues. Or could vehicle had been in deep water, possible a flood. Without any carfax or service history to indicate anything unusual, perhaps! But typically these blocks hold-up very well, unless disturbed.

Point being. We must try to find and understand why a component fails, so we can correct the "why" as we fix the issue.

Most all wire housing blocks are available from Toyota/Lexus. So are the pigtails (wire leads).

I'd disconnect wire block from sides of transmission. Testing contine from AT end to CPU and replays. Target corrosion block first, which may save time. You may want to check the wire from transfer case also.

Here's where it gets tricky. Just because it has continuity, doesn't mean the resistance is not higher than it should be. Resistance can be to high reduce current read by CPU, due to a connection with oxidation/corrosion or even some of the strands within wire sheathing being damaged. Which we should see some outside signs of (chew marks, burn, rub, crush, etc.) yet still show continuity. Knowing the resistance (OHMs), may or may not be in FSM. Some will be in diagnostic section. Where it will have test for OHM at specific temperature range.

Note: Aircraft technician, use new wire harnesses to compare resistance to those within the aircraft. My Toyota parts guy is great guy. I can buy for testing & return, as long as working and saleable.

Note the while plastic lock on LH wire housing block

IIRC you had CDL DTC, which CDL SW as at end of below wire harness. Possible clue!

Engine side of AT wire, main wire harness

AT side of AT wire harness

I splice wires with water tight seal & soldier like this:

 

[MongooseGA]

As you work on wiring. Keep in mind, the wire housing block(s) with corrosion inside. Corrosion inside means, either the seal failed or it was not fully seat making a good seal. The block on LH (driver side) has a very special locking mechanism. Which indicates Toyota engineers were very concerned with that block prehas with moisture. For some reason in that one, more than the others.

I would think your issue, began at a time one or more of these were disconnected and then not fully seated when reconnected. Perhaps making a good enough contact/continuity, no faults at the time. Then over time, moisture made its way into housing block.

There are only a few services, where one or more would have been disconnected. One bing (but not needed), is starter R&R. Others are engine or transmission R&R. Even could have been diagnostics work in the pasted. Knowing a vehicles service history and carfax history, has value in diagnostic.

I'll note: I did see one 01LX, that had history of electrical gremlins. It's the one I pictured AHC wire harness block corrosion. It's history showed various electronic issues, starting while still under warranty period. We don't know why, these wire housing blocks seals were failing. Was it a freak factory issues. Or could vehicle had been in deep water, possible a flood. Without any carfax or service history to indicate anything unusual, perhaps! But typically these blocks hold-up very well, unless disturbed.

Point being. We must try to find and understand why a component fails, so we can correct the "why" as we fix the issue.

Most all wire housing blocks are available from Toyota/Lexus. So are the pigtails (wire leads).

I'd disconnect wire block from sides of transmission. Testing contine from AT end to CPU and replays. Target corrosion block first, which may save time. You may want to check the wire from transfer case also.

Here's where it gets tricky. Just because it has continuity, doesn't mean the resistance is not higher than it should be. Resistance can be to high reduce current read by CPU, due to a connection with oxidation/corrosion or even some of the strands within wire sheathing being damaged. Which we should see some outside signs of (chew marks, burn, rub, crush, etc.) yet still show continuity. Knowing the resistance (OHMs), may or may not be in FSM. Some will be in diagnostic section. Where it will have test for OHM at specific temperature range.

Note: Aircraft technician, use new wire harnesses to compare resistance to those within the aircraft. My Toyota parts guy is great guy. I can buy for testing & return, as long as working and saleable.

Note the while plastic lock on LH wire housing block
View attachment 3760917
IIRC you had CDL DTC, which CDL SW as at end of below wire harness. Possible clue!
View attachment 3760918
Engine side of AT wire, main wire harness
View attachment 3760940
AT side of AT wire harness
View attachment 3760921

I splice wires with water tight seal & soldier like this:

Interesting. I have had the starter replaced and had my transfer case out once or twice (prior to all of this).

When I'm running these tests, am I unplugging all 3 of those connections prior to putting a meter on it, or leaving everything but the test connection plugged in?

 

[LJE]

Interesting. I have had the starter replaced and had my transfer case out once or twice (prior to all of this).

When I'm running these tests, am I unplugging all 3 of those connections prior to putting a meter on it, or leaving everything but the test connection plugged in?

I'd leave everything else plugged in.

 

[2001LC]

By the book, would test from far end to far end. End where plugs to AT or TC and other at CPU or relay. One wire or wire housing plug at a time. Once one point found with no continuity or high resistance. Then work to isolate that wire and or wire housing block.

I'd likely jump to most suspect points first. To see if I get lucky!

 

[MongooseGA]

By the book, would test from far end to far end. End where plugs to AT or TC and other at CPU or relay. One wire or wire housing plug at a time. Once one point found with no continuity or high resistance. Then work to isolate that wire and or wire housing block.

I'd likely jump to most suspect points first.

I'm trading my favorite Lexus master tech some delicious smoked pork belly this weekend for a few hours of his help going through everything and doing the testing. Harness should be here by then should we have the need to replace it.

 

[LJE]

I'm trading my favorite Lexus master tech some delicious smoked pork belly this weekend for a few hours of his help going through everything and doing the testing. Harness should be here by then should we have the need to replace it.

Come up to Indiana & I'll smoke the pork belly for ya and do the diagnosis!

...just better watch that frame weight while I'm under your truck...

 

[MongooseGA]

Come up to Indiana & I'll smoke the pork belly for ya and do the diagnosis!

...just better watch that frame weight while I'm under your truck...

Shoot, you could just have it at that point.

 

[MongooseGA]

Updates: @Wermz came by last night and we tested the wiring. Long story short, I'm looking at ECM.

There's a guy locally that the dealers use to rebuild them, I'll call him tomorrow. There's also a group out of Indiana (I think? ) that I've already spoken to about rebuilding.

Hopefully we're getting to the end here.

 

[LJE]

Updates: @Wermz came by last night and we tested the wiring. Long story short, I'm looking at ECM.

There's a guy locally that the dealers use to rebuild them, I'll call him tomorrow. There's also a group out of Indiana (I think? ) that I've already spoken to about rebuilding.

Hopefully we're getting to the end here.

Really? That's wild! Figured the wiring was far more likely than the ECM.

 

[MongooseGA]

Really? That's wild! Figured the wiring was far more likely than the ECM.

Even all of the connectors appeared pristine inside, no cracking, not even brittle, no visible corrosion.

So, interestingly, if it is in fact the ECM, this is actually a not- uncommon problem in similar year LS430s. And it's almost always the ECM. Ryan, being a former Lexus master tech, has a bunch of Toyota tech buddies. Last night he texted and called a few, posed the situation and asked "what's the first thing you do? ". Consistently, all of them said "ECM".

Obviously we'd have more reason to believe my issue could lie in the wiring, just due to the way the truck is used. Submerged in GA clay, over the hood water crossings, chassis slamming on rocks, etc. But, if this ECM is the ticket, I'll be glad for an easy solution out of it. Gerry is going to get a gift of some kind after she's fixed for her patience. After my next closing

 

[Malleus]

I'd be interested who in Indiana is rebuilding ECMs. Actually very interested.

There's a group in Greenville, SC rebuilding Toyota RAV4 ECMs (for some reason), but they haven't rebuilt any Land Cruiser ECMs. I'm trying to get them interested.

 

[MongooseGA]

I'd be interested who in Indiana is rebuilding ECMs. Actually very interested.

There's a group in Greenville, SC rebuilding Toyota RAV4 ECMs (for some reason), but they haven't rebuilt any Land Cruiser ECMs. I'm trying to get them interested.

SIA Electronics | ECU Repair for all Makes and Models

SIA Electronics provides ECU Repair and return for all makes and models at competitive price. Call (800)737-0915.

siaelec.com

I have NO affiliation and have not used them yet.

 

[LJE]

That's Illinois buddy. That's it, I formally rescind any offer of my help. I wont standby to have my state malinged like that.

 

[MongooseGA]

That's Illinois buddy. That's it, I formally rescind any offer of my help. I wont standby to have my state malinged like that.

What's the difference?


Hey, I said "I think"!. I knew it was Midwestish, started with an I.  

 

[MongooseGA]

I reached out to the local guy who rebuilds the ECMs. $195 fee and he says a 1 day turnaround. Fingers crossed we get this old girl wrapped up this week.

 

[2001LC]

Update from the trans shop:


He just mentioned to me that he noticed some coolant drippage on the trans wiring harness connector at the top of the trans. Disconnected, cleaned it up some,

"Disconnected, cleaned it up some,"
I assumed and didn't you also write somewhere. The connector (wire housing block) had some signs of contamination inside?

 

[Eyedaho]

I reached out to the local guy who rebuilds the ECMs. $195 fee and he says a 1 day turnaround. Fingers crossed we get this old girl wrapped up this week.

Interesting that it's a low fixed price and quick turnaround. Makes me think there's a common failure component like an electrolytic capacitor or cracked trace or something cheap and easy to replace.