5-speed A750 trans won't shift in to 5th gear. (1 Viewer)

[MongooseGA]

That doesn't shock me - best we can tell, your transfer case has zero idea what position it's in, hahaha.

Definitely getting more suspicious of water intrusion issues though.

Agreed. FWIW I've never had a single issue with the truck going in to low or back to high range. Never a jam or stuck linkages, and they're pretty regularly exercised. I just cycled through both trans gears and really made an effort shove the lever with some gusto. Not necessary to get it in to gear, but maybe it would smack the sensor a little better No dice.

I keep going back to ordering that originally-discussed harness from trans to case..

Update on the P/N from my Lexus Tech buddy- the computer sees P and N as the same, with P just having the pawl to keep the trans from moving. So while in park, it should read as it is now.

 

[LJE]

Agreed. FWIW I've never had a single issue with the truck going in to low or back to high range. Never a jam or stuck linkages, and they're pretty regularly exercised.

I keep going back to ordering that originally-discussed harness from trans to case..

I don't doubt that - one of the benefits of a purely mechanical system (vs the electric actuators for low range on a 4th gen 4 runner, for example...).

 

[MongooseGA]

I don't doubt that - one of the benefits of a purely mechanical system (vs the electric actuators for low range on a 4th gen 4 runner, for example...).

Reading through a bunch of 200 threads for the same 2 code, I'm definitely grateful for the lever actuator vs the dial/button.

 

[LJE]

Agreed. FWIW I've never had a single issue with the truck going in to low or back to high range. Never a jam or stuck linkages, and they're pretty regularly exercised. I just cycled through both trans gears and really made an effort shove the lever with some gusto. Not necessary to get it in to gear, but maybe it would smack the sensor a little better No dice.

I keep going back to ordering that originally-discussed harness from trans to case..

Update on the P/N from my Lexus Tech buddy- the computer sees P and N as the same, with P just having the pawl to keep the trans from moving. So while in park, it should read as it is now.

comment on your update: Interesting. I wonder why it would throw that code with things in park? That seems strange to me (but, to be fair, so does this entire situation...). With the code cleared, can you cycle the T-case back and forth (with the trans in park) without the code popping back up?

 

[MongooseGA]

comment on your update: Interesting. I wonder why it would throw that code with things in park? That seems strange to me (but, to be fair, so does this entire situation...). With the code cleared, can you cycle the T-case back and forth (with the trans in park) without the code popping back up?

I'll try to clear it again and give this a shot. I don't believe I've ever changed the case while trans was not in neutral. I just wish I knew what I did to get it cleared to begin with lol

 

[MongooseGA]

New sensor is delayed so I'll put the shaft back in, pull her in the garage and continue messing with it.

 

[MongooseGA]

Curiouser and curiouser...

This afternoon I pulled Gerry (that's the truck's name, not mine!) into the garage and reinstalled the rear drive shaft. When I let the ass end down, I let it come down pretty quick and hard (this may be pertinent). Started the engine, turned off CDL, and took her for a spin. Wouldn't ya know it, the trans shifted in to 5th. I even confirmed this by dropping to 4th manually, then back to 5th several times.

Before getting excited I ran home, picked up the dog for a ride, and went back out. Did not turn off the engine. On second trip, trans wouldn't shift to 5th again.

So I don't really know what I did, other than maybe dropping the truck jarred/wiggled something into correct position, then it moved again while driving. To me this sounds like electrical short possibly, but I'm a mechanical idiot trying to punch-up currently.

 

[MechE30]

Curiouser and curiouser...

This afternoon I pulled Gerry (that's the truck's name, not mine!) into the garage and reinstalled the rear drive shaft. When I let the ass end down, I let it come down pretty quick and hard (this may be pertinent). Started the engine, turned off CDL, and took her for a spin. Wouldn't ya know it, the trans shifted in to 5th. I even confirmed this by dropping to 4th manually, then back to 5th several times.

Before getting excited I ran home, picked up the dog for a ride, and went back out. Did not turn off the engine. On second trip, trans wouldn't shift to 5th again.

So I don't really know what I did, other than maybe dropping the truck jarred/wiggled something into correct position, then it moved again while driving. To me this sounds like electrical short possibly, but I'm a mechanical idiot trying to punch-up currently.

I also am a mechanical minded idiot and to me I would put some cash on that bouncing something physical loose internal to the trans. Idk, again, I’m a hammer and everything is a nail.

 

[MongooseGA]

I'm ordering the harness in question on Monday. I think my Ms is getting tired of hearing about it

 

[LJE]

I also am a mechanical minded idiot and to me I would put some cash on that bouncing something physical loose internal to the trans. Idk, again, I’m a hammer and everything is a nail.

That would be my guess, except that @MongooseGA has said that the truck doesn't even try to shift to 5th (unlike when the main ECM was bad).

To me, that means that something is telling the computer to stay out of 5th gear entirely.

I asked him to connect techstream again and verify that the tranmission reads that it should be in "drive" when he shifts the lever to D. It'd be funny if the shift position sensor was reading that he had shifted to 4 instead, haha. Though I guess I would suspect that "D" wouldn't light up on the dash then. Still, worth a check IMO.

 

[MongooseGA]

. Though I guess I would suspect that "D" wouldn't light up on the dash then. Still, worth a check IMO.

Can confirm that the truck recognizes which gear the selector is in for the trans. I could not find anything to show live data about the transfer case. It's possible I looked over it or didn't recognize however it was labeled.

OK so computer brain knows the selector is in D. That's good. So why in 4th? Brings me back to communication from L4 switch to brain. Between those are the harness and the ABS module.

There's a possibility that there's something in the brake system causing the issue, but I believe the ABS code commonly accompanies the L4 pickup code.

 

[LJE]

Here's an idea if you want to get froggy: you know the L4 position sensor pin (EXI2) that you've been probing at the skid control computer? Unplug that connector from the skid control computer, use a depinning tool and pop just that one pin out of the connector, wrap it in some electrical tape (to make sure it doesn't short to anything), plug the connector back into the skid control computer, and see what happens.
At that point the L4 switch & harness cannot feed the skid control computer bad data. Since all that switch does is connect that pin to battery voltage when in low gear, pulling the wire should mimic the transfer case being in 'high'.

 

[MongooseGA]

I can try this. In lieu of an actual depinning tool, what's a safe way to do it without damaging the pin or connector?

I've wondered if there's any reason that a missing or otherwise incorrect signal would for some reason default to low range spec.

 

[Malleus]

Either one of these will work:

 

[MongooseGA]

Sweet, I have those.

It'll be later in the day but I'll do it this evening.

 

[LJE]

I can try this. In lieu of an actual depinning tool, what's a safe way to do it without damaging the pin or connector?

I've wondered if there's any reason that a missing or otherwise incorrect signal would for some reason default to low range spec.

I guess the first step would be to measure voltage at that pin with the T-case in high and see what you get - should be a 0 volt difference between ground and that pin in high.

 

[MongooseGA]

I guess the first step would be to measure voltage at that pin with the T-case in high and see what you get - should be a 0 volt difference between ground and that pin in high.

Once removed or still in situ?

 

[LJE]

Once removed or still in situ?

Still in situ. Exact same procedure as what you've been doing to measure the voltage in low gear at that pin, but with the case in high.

 

[Slap Back]

Curiouser and curiouser...

This afternoon I pulled Gerry (that's the truck's name, not mine!) into the garage and reinstalled the rear drive shaft. When I let the ass end down, I let it come down pretty quick and hard (this may be pertinent). Started the engine, turned off CDL, and took her for a spin. Wouldn't ya know it, the trans shifted in to 5th. I even confirmed this by dropping to 4th manually, then back to 5th several times.

Before getting excited I ran home, picked up the dog for a ride, and went back out. Did not turn off the engine. On second trip, trans wouldn't shift to 5th again.

So I don't really know what I did, other than maybe dropping the truck jarred/wiggled something into correct position, then it moved again while driving. To me this sounds like electrical short possibly, but I'm a mechanical idiot trying to punch-up currently.

Hmmmm....if dropping it helped, maybe try this. lol

 

[MongooseGA]

Been texting with LJE but updating here as well.

I didn't find my tiny jeweller's drivers, so tried a paperclip to depin instead. No luck, clip didn't have the rigidity to move the lock on the pin (yes I did release the locking bar on the back side of the connector) . I'll get a depin tool kit to be safe, I can easily see screwing this up without the right tool.

I did get a better back probe reading on the connector going to the ABS ecu. Initially I'd only read it in high range which obviously isn't what was needed. I found a much better body ground to use, and can confirm now that the wire is giving 13v (goal is 10-14v) in low range. Interestingly, it also gives 3.7v in high, which, per Alex, should only show 0v.

I also found that the codes can be cleared if I catch a key cycle where they don't pop on the dash at start up. They seem to be very inconsistent, so every couple of key cycles will yield a clean dash.

I cleaned both ends of the connector to the ABS ecu (wiring side and ecu side). I also disconnected all the wiring on the brake booster/ MC and cleaned those. And I cleaned my battery posts and terminals.

With no codes present and no lights on the dash, there is still no 5th. I had TS hooked up during a drive and watched the computer recognize the shifts from 1-4, but the truck never tried or thought it had gone to 5th.