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

[hoser]

Learn something new everyday. What would we think is a reason for Toyota to lock out top gear/ OD for low range?

Typically, the transmission is strongest in 1:1 ratio. Going to overdrive in the transmission and winding out the transfer case could overheat the t-case. The transfer case only has like ~1.5 Quarts capacity. But if you have re-geared both the diffs and the transfer case, I can understand the desire to want the overdrive.

 

[Import Driver]

So, to put a bow on it: this was all due to a faulty ECU?

All because he sneezed without covering his mouth and the humidity from it ruined the ECU.

 

[jpneely]

Hell yea! Congrats buddy, that’s got to feel good after all that troubleshooting and tranny swapping. Thanks for keeping us up to date!

 

[LJE]

My favorite part of this was learning that @MongooseGA 's LX and mine were built in the same month.

I can only imagine that they were long-lost assembly line buddies, and my truck getting his ECM transplanted temporarily into it must have been like the weirdest sibling reunion ever.

 

[MongooseGA]

I like to think they each remember each other like I do my kindergarten best friend Mike Milner. Haven't seen him in 30 years, but I'm sure he's still really cool and I'd totally have a beer with him now.

 

[MongooseGA]

Well **** me.


Trans won't shift in to 5th again.

I queried some cruiser friends smarter than I and the consensus is "idk man that really sucks"

There's no slamming in to gear from 2-1 like there had been, and I'd been driving the truck for errands earlier in the day with no issue. Picked up steel from my supplier about half an hour away and as soon as I pulled out of their parking lot, it would no longer shift up to top gear.

There is a downshift with the throttle, unlike the last time around.

Thoughts are that maybe the old wiring harness is actually intermittently bad, and as soon as whatever error/short happens, the ecm goes kaput. No codes on the SG again so I'm going to try to meet up with Patch to borrow his TS laptop.

CEL, VSC TRAC and VSC OFF lights have been on and off with key cycles for a week. I'd assumed it was due to the ABS speed sensor code that was pulled during the trans swap, but maybe it's related. Also no codes on SG.

So, feeling cool.

 

[Malleus]

Just a thought, because I went through this with my '08 LX570, if you haven't done this: check every connector housing in the ECU area, including the ones behind the passenger kickpanel, I mean take them apart and visually inspect the terminals. My sunroof drains leaked onto the passenger corner and I had to replace the engine and cowl harness.

I was amazed (sickened, actually) at how badly they were corroded. They could have been cleaned, if I had taken the time to depin every one of them and polish them individually. Allstate paid for new wire, so I elected not to.

 

[Foehammer]

That's f*cking sh*tty. I'd be really tempted to sell the damn thing.

 

[Malleus]

I was; my daughter has it. I got the '94 80 I gave her for graduation. We're both happy.

 

[MongooseGA]

Just a thought, because I went through this with my '08 LX570, if you haven't done this: check every connector housing in the ECU area, including the ones behind the passenger kickpanel, I mean take them apart and visually inspect the terminals. My sunroof drains leaked onto the passenger corner and I had to replace the engine and cowl harness.

I was amazed (sickened, actually) at how badly they were corroded. They could have been cleaned, if I had taken the time to depin every one of them and polish them individually. Allstate paid for new wire, so I elected not to.

I can do this.

That's f*cking sh*tty. I'd be really tempted to sell the damn thing.

For myriad reasons, I likely won't, but I've definitely been rolling the idea around.

 

[LJE]

Texting with GA, my best guess is that considering both the ECM and the SR solenoid are 'new', the most logical place for the problem to lie is somewhere in the wiring harness. We know for sure that his old ECM was bad (confirmed by swapping into my truck), but yet the FSM says that you can get a code for when you have a solenoid that's shorted - so it would seem like it should have protection against a short causing an internal MOSFET or BJT (perhaps part of an larger IC) to be required to supply effectively infinite current.

However, I'm curious if there's a SUPER short duration electrical short periodically happening between a pair of wires - fast enough to not trigger a code, but each time it happens it would be doing slight damage to an internal ECM component. Do enough cycles of that, and you've blasted enough angry electrons through the IC that it fails.

@Malleus point of connectors being all corroded seems much more likely, but I'm not sure why that would end up toasting an ECM - seems like if you had a corroded connection providing a high resistance, than current would be lower (I=V/R). While it may reach a threshold where it no longer could trigger the solenoid, I wouldn't think it would destroy your ECM. Either way, a resistance check at the ECM connector while someone wiggles wires might tell you something. (like I've been saying for several pages now )

 

[MongooseGA]

Like I said, smarter than I.

 

[LJE]

Like I said, smarter than I.

Unlikely, just more experienced with electrons (which, while annoying, still confused me less than photons).
If ya need a refresher, this video breaks it down pretty well in an automotive related environment:
You can do just about everything you'd need to do on a car with a pretty basic multimeter.

 

[Malleus]

Two unrelated, coincidental failures?

 

[MongooseGA]

Two unrelated, coincidental failures?

Non-zero possibly, but I feel not likely.

 

[97 AZ LC]

I think it's time to upgrade to a four speed.

 

[riffman12]

this thread made me panic yesterday when my 5 speed was cold and held 4th for a fraction longer before hitting 5th.

Hope you find the solution soon.

 

[MongooseGA]

this thread made me panic yesterday when my 5 speed was cold and held 4th for a fraction longer before hitting 5th.

Hope you find the solution soon.

So before this most recent occurrence, I had a very similar thought when it did the same on a very cold morning. I'd even made a comment to my Ms that it felt like this new trans held 4th a tiny bit longer than the old one did.

 

[2001LC]

I don't recall was EUC rebuild or used or new. If not new, reman may have failed again. Used not to likely to fail on it's own.

Likely a short, if was new ECU!

The reason I asked. If you could think of anything that would have caused ECU to fail/short.
1) Toyota teaches, to look for cause of a failure. So one can correct, so doesn't reoccur.

Your hard driving off-road, isn't likely cause. This are tanks. Other than jossiling a loose connection or harness. It's why Toyota locks and ties, all wires and wire housing blocks.

Any water entry into cabin, is a possibility. A one time leak/wetting, usually drys-out and all is good. But, leaks that keep reapplying water, cause all kinds of issues. These result in oxidation on leads. Which may be on hot wire lead, or a ground or ground fault bus.

Aftermarket wiring, often causes issues. So needs, a close look.

Always disconnect battery, before disconnecting or connect or working on anything that is electrical.

 

[MongooseGA]

I don't recall was EUC rebuild or used or new. If not new, reman may have failed again. Used not to likely to fail on it's own.

Likely a short, if was new ECU!

The reason I asked. If you could think of anything that would have caused ECU to fail/short.
1) Toyota teaches, to look for cause of a failure. So one can correct, so doesn't reoccur.

Your hard driving off-road, isn't likely cause. This are tanks. Other than jossiling a loose connection or harness. It's why Toyota locks and ties, all wires and wire housing blocks.

Any water entry into cabin, is a possibility. A one time leak/wetting, usually drys-out and all is good. But, leaks that keep reapplying water, cause all kinds of issues. These result in oxidation on leads. Which may be on hot wire lead, or a ground or ground fault bus.

Aftermarket wiring, often causes issues. So needs, a close look.

Always disconnect battery, before disconnecting or connect or working on anything that is electrical.

Worth mentioning, there was no rain in the time between putting in the new (used) ECU and this reoccurring.

Possible the new(used) ecm went bad on its own but that it did so in the exact same manner is a head scratcher, unless caused by existing problem in the truck.

At this point, I've changed the transmission control module, the ECM, and the complete trans. The only thing not changed is the trans wiring harness.

Pulling codes at @cruiserpatch 's place now and this is all that comes up. No longer a solenoid code.