5-speed A750 trans won't shift in to 5th gear. (31 Viewers)

[jLB]

Imagine if you had a really nice 80 with a couple problems... But you sold it 10 years ago before the value went way up.

I bought a 94 80 series new, and traded it in after 10 years of ownership, and ~100k miles, due to 3 consecutive months with $1k repairs. At the time I believe that it was valued in the low teens. Driving my father’s shiny new 98 LX470, back to back with my 80 series didn’t help. Maybe that’s why I’m a little “clingy” about my 100 series, something like “cold dead hands” comes to mind.

 

[Kbaards]

Hello! New member, just joined to comment. Holy cow your dedication to this LX is impressive.

I have a 2005 gx470 with the harsh shift into 1st and no 5th gear. Iv only had it a couple months and have been pulling my hair out trying to figure out the problem. I have the p0771 and a p2759 resistance code. I have tried all the things - Fluid, new solenoids new wiring harnesses. I didn't think the resistance code was my main problem. But maybe the codes have been telling me its the ecm this whole time. I was just getting ready to rebuild the valve body when I found this thread. I now am looking at getting my ECM rebuilt or finding one to swap in.

I am a little concerned that this was originally a ECM issue but since the previous owner delayed for 13k miles and just drove around like this that real damage has been done to the transmission or TC. Fingers crossed it's just the ECM.

Thanks for all the info in this thread!

 

[MongooseGA]

Hello! New member, just joined to comment. Holy cow your dedication to this LX is impressive.

I have a 2005 gx470 with the harsh shift into 1st and no 5th gear. Iv only had it a couple months and have been pulling my hair out trying to figure out the problem. I have the p0771 and a p2759 resistance code. I have tried all the things - Fluid, new solenoids new wiring harnesses. I didn't think the resistance code was my main problem. But maybe the codes have been telling me its the ecm this whole time. I was just getting ready to rebuild the valve body when I found this thread. I now am looking at getting my ECM rebuilt or finding one to swap in.

I am a little concerned that this was originally a ECM issue but since the previous owner delayed for 13k miles and just drove around like this that real damage has been done to the transmission or TC. Fingers crossed it's just the ECM.

Thanks for all the info in this thread!

The harsh first gear does make me think ECM before all else. It would be nice if they weren't so pricey for a good one or rebuilt one.

You might see if there is anyone in your neck of the woods who is willing to lend you an ECM to test. It must be the exact part number as what's in your truck now. There's a handshake procedure each time an ECM goes in to a new truck, but it's pretty simple. If the ECM solves your problem, you're good to go. If not, I'd visually check the wiring harness that runs the drivers side of the transmission and eventually goes across to the transfer case. It connects to 3 big points at the firewall, directly on top of the transmission. Really easily visible from the top of the engine.

Best of luck. I'll be thrilled if the info in this thread saves one other guy.

 

[Kabanstva]

The harsh first gear does make me think ECM before all else. It would be nice if they weren't so pricey for a good one or rebuilt one.

You might see if there is anyone in your neck of the woods who is willing to lend you an ECM to test. It must be the exact part number as what's in your truck now. There's a handshake procedure each time an ECM goes in to a new truck, but it's pretty simple. If the ECM solves your problem, you're good to go. If not, I'd visually check the wiring harness that runs the drivers side of the transmission and eventually goes across to the transfer case. It connects to 3 big points at the firewall, directly on top of the transmission. Really easily visible from the top of the engine.

Best of luck. I'll be thrilled if the info in this thread saves one other guy.

This thread is way too long to read everything. What ended up being the issue that caused your trans not to go into 5th? ECU?

 

[MongooseGA]

This thread is way too long to read everything. What ended up being the issue that caused your trans not to go into 5th? ECU?

Combination of ECM and the main wiring harness going to the transmission. Possibly some sensors on the trans as well.

 

[Kbaards]

The harsh first gear does make me think ECM before all else. It would be nice if they weren't so pricey for a good one or rebuilt one.

You might see if there is anyone in your neck of the woods who is willing to lend you an ECM to test. It must be the exact part number as what's in your truck now. There's a handshake procedure each time an ECM goes in to a new truck, but it's pretty simple. If the ECM solves your problem, you're good to go. If not, I'd visually check the wiring harness that runs the drivers side of the transmission and eventually goes across to the transfer case. It connects to 3 big points at the firewall, directly on top of the transmission. Really easily visible from the top of the engine.

Best of luck. I'll be thrilled if the info in this thread saves one other guy.

I have an update for my GX. I found a used ECM on ebay with matching part numbers and just swapped it in. This has made a huge improvement but not solved the issue completely. I no longer have code P2759 for the "torque converter clutch pressure control solenoid circuit electrical". this code used to show up instantly after being cleared and now with the new ECM its gone, YAY! drivability has drastically improved. it's no longer slamming into 1st, still slightly noisy but not shaking the whole car when you go into drive from park. its shifting very nicely up and down through all gears EXCEPT 5th. so still no 5th Gear. but something strange that's different with the new ECM is I feel like I can feel the car trying to shift into 5th. around 55mph, moving from 4th to D I can feel the car slow, RPMs drop a little for about a second. Pending Code P0771 shows up after test driving. "Shift Solenoid E Stuck Off"

I'm looking for help on what to try next. here's everything I've done in order since purchasing: Full ATF flush and filter change. pulled and tested all solenoids to be within OHMS and works when hotwired. Replaced the internal wiring harness for the solenoids. Inspected wiring harness connector on the side of the transmision. Tested OHMS at ECM connector for some of the Solenoids. Replaced ECM.

Following a FSM I found online the only step I haven't done (besides replacing the transmission) for code P0771 is to "Inspect Transmission Valve Body Assembly". I'm again considering doing a Valve Body rebuild with one of these Kits TransGo - Toyota A750 SHIFT KIT® Valve Body Repair Kit with tools - https://transgo.com/product-details/toyota-a750-shift-kit/

This transmission does have almost 250K miles on it. The fluid didn't look great when i flushed it. my guess is it had never been serviced. so It wouldn't be crazy to assume some of the valves have a high level of wear and that could be causing this issue.

 

[MongooseGA]

This does sound pretty similar to my issue. After putting in one new ecm, I did have full transmission function but only for about a week before it went back to no 5th and hard shifting (hard shifting wasn't an issue on original ecm).

Ultimately it was the external wiring harness that made the difference for me. If the GX is the same as the 100, you'll see 3 big connections at the top of the bellhousing. Lay flat on the engine and look straight down from the firewall. This harness also has connections on the transfer case.

Now, I did the harness at the same time I replaced some of the sensors. Even though I'd tested the sensors as good, it was cheap insurance to just swap in new ones. So I cannot 100% definitively say what the fix was, but it was definitely one of those items replaced at the same time.

 

[Kbaards]

This does sound pretty similar to my issue. After putting in one new ecm, I did have full transmission function but only for about a week before it went back to no 5th and hard shifting (hard shifting wasn't an issue on original ecm).

Ultimately it was the external wiring harness that made the difference for me. If the GX is the same as the 100, you'll see 3 big connections at the top of the bellhousing. Lay flat on the engine and look straight down from the firewall. This harness also has connections on the transfer case.

Now, I did the harness at the same time I replaced some of the sensors. Even though I'd tested the sensors as good, it was cheap insurance to just swap in new ones. So I cannot 100% definitively say what the fix was, but it was definitely one of those items replaced at the same time.

Can you link what sensors you replaced? How difficult is replacing that external wiring harness? From what I can tell it's mostly on top of the transmission?

Anyone have a theory as to why with the new ECU I can feel the car trying to shift into 5th?

 

[MongooseGA]

Can you link what sensors you replaced? How difficult is replacing that external wiring harness? From what I can tell it's mostly on top of the transmission?

Anyone have a theory as to why with the new ECU I can feel the car trying to shift into 5th?

The harness was much easier to replace than I'd anticipated. Probably took me 20 minutes with my Ms up top helping to fish the harness down to me as I made the connections. Everything is relatively easy to access and what's not visible is still pretty reachable with fingers.

I wish I knew why it feels like it wants to shift. I felt the same thing which is part of why I felt it wasn't a mechanical issue in my case. My suspicion, which is worth nothing, is that the truck is putting itself in to a limp mode for one reason or another. One of those reasons could be the 5th gear lock out in low range. There's a pair of plunger style sensors on the case that are responsible for this. They can be 'cleaned' with electrical current, I may have instructions here. Mine tested bad before cleaning, good afterwards. But were ultimately replaced. I've considered that a fault in the wiring to either of these sensors can give the same outcome as a bad sensor, which is the same end result as being in 4-Lo: no 5th gear.

 

[Kbaards]

The harness was much easier to replace than I'd anticipated. Probably took me 20 minutes with my Ms up top helping to fish the harness down to me as I made the connections. Everything is relatively easy to access and what's not visible is still pretty reachable with fingers.

I wish I knew why it feels like it wants to shift. I felt the same thing which is part of why I felt it wasn't a mechanical issue in my case. My suspicion, which is worth nothing, is that the truck is putting itself in to a limp mode for one reason or another. One of those reasons could be the 5th gear lock out in low range. There's a pair of plunger style sensors on the case that are responsible for this. They can be 'cleaned' with electrical current, I may have instructions here. Mine tested bad before cleaning, good afterwards. But were ultimately replaced. I've considered that a fault in the wiring to either of these sensors can give the same outcome as a bad sensor, which is the same end result as being in 4-Lo: no 5th gear.

Thanks for the reply! I think I will try replacing the speed sensors and the low-high sensor next. I can't find the part number for the low-high sensor anywhere. Does anyone have a link or the part number?

 

[emorth]

Just a thought... Not sure if this applies.
I had a first gen 4R that would not shift into overdrive. Turns out the ECM will not let the transmission controller shift the transmission into overdrive until the engine is up to temperature. Fixing a loose/dirty connection on the temp sensor on the engine solved the problem. This sensor is separate from the temp sensor for the dashboard temp gauge. The previous owner sold it to me for cheap because it had a "transmission" problem. He took it to various transmission shops and non of them could fix the "transmission" problem. I can't image what that cost him??? It took some high tech diagnostics to figure out what was going on but the fix was supper easy and free.
Hope this helps..

 

[MongooseGA]

Thanks for the reply! I think I will try replacing the speed sensors and the low-high sensor next. I can't find the part number for the low-high sensor anywhere. Does anyone have a link or the part number?

I tried to post all part numbers in this thread as I went. Search my username in this thread and whichever item you need the PN for, they should pop up. Good luck with the sensors! They're a pretty easy swap.

Just a thought... Not sure if this applies.
I had a first gen 4R that would not shift into overdrive. Turns out the ECM will not let the transmission controller shift the transmission into overdrive until the engine is up to temperature. Fixing a loose/dirty connection on the temp sensor on the engine solved the problem. This sensor is separate from the temp sensor for the dashboard temp gauge. The previous owner sold it to me for cheap because it had a "transmission" problem. He took it to various transmission shops and non of them could fix the "transmission" problem. I can't image what that cost him??? It took some high tech diagnostics to figure out what was going on but the fix was supper easy and free.
Hope this helps..

I've read about this before, but never experienced it myself in the 100.

 

[Kbaards]

Small update! I have a faulty L4 switch. I finally found it, I believe the transfer cases on the GX is different then the 100. The switches are different then the photos you posted. I found a diagram from a fjcruiser and that appears to match the transfer case in my GX. But after finally figuring out where the l4 switch is, I pulled the connector and tested the switch and it's in the open position permanently. I just ordered a new switch off of eBay, fingers crossed this will get me 5th gear!

 

[MongooseGA]

Small update! I have a faulty L4 switch. I finally found it, I believe the transfer cases on the GX is different then the 100. The switches are different then the photos you posted. I found a diagram from a fjcruiser and that appears to match the transfer case in my GX. But after finally figuring out where the l4 switch is, I pulled the connector and tested the switch and it's in the open position permanently. I just ordered a new switch off of eBay, fingers crossed this will get me 5th gear!

This is a great step! I'll hold super excitement until after, as my switches had also tested bad and cleaning them (and subsequently testing them as good) didn't fix the issue.

If this is your fix, congrats. That's an easy one. But, if it's not, I still think you're on the right path and there's not a whole lot more to consider that hasn't been already.

 

[Kbaards]

This is a great step! I'll hold super excitement until after, as my switches had also tested bad and cleaning them (and subsequently testing them as good) didn't fix the issue.

If this is your fix, congrats. That's an easy one. But, if it's not, I still think you're on the right path and there's not a whole lot more to consider that hasn't been already.

Swapped in the new L4 switch today and still no 5th gear! tested the old one and confirmed it was toast. tested the new one and confirmed its working. i would like to test it back at the ABS Module but I'm having trouble finding those pins. I have the OBD Fusion app set up to show me the status of the HIGH/Low Shifter and its still telling me its in low permanently. After test driving the P0771 code didn't come back but i had a 02 Sensor code show up that was new. i did wiggle some wires when replacing the L4 switch so i may have caused that. the lunge into 1st has gotten worse with a little bit of driving. so i'm thinking the external wiring harness is bad and i am going to replace that next.

I need some help finding a part number. I cant even find the part with a google search. a part number, supplier or even verbiage to help find the part through google would be very helpful.

Thanks!

 

[Bisho]

Swapped in the new L4 switch today and still no 5th gear! tested the old one and confirmed it was toast. tested the new one and confirmed its working. i would like to test it back at the ABS Module but I'm having trouble finding those pins. I have the OBD Fusion app set up to show me the status of the HIGH/Low Shifter and its still telling me its in low permanently. After test driving the P0771 code didn't come back but i had a 02 Sensor code show up that was new. i did wiggle some wires when replacing the L4 switch so i may have caused that. the lunge into 1st has gotten worse with a little bit of driving. so i'm thinking the external wiring harness is bad and i am going to replace that next.

I need some help finding a part number. I cant even find the part with a google search. a part number, supplier or even verbiage to help find the part through google would be very helpful.

Thanks!

Partsouq.com is your friend.

 

[MongooseGA]

Swapped in the new L4 switch today and still no 5th gear! tested the old one and confirmed it was toast. tested the new one and confirmed its working. i would like to test it back at the ABS Module but I'm having trouble finding those pins. I have the OBD Fusion app set up to show me the status of the HIGH/Low Shifter and its still telling me its in low permanently. After test driving the P0771 code didn't come back but i had a 02 Sensor code show up that was new. i did wiggle some wires when replacing the L4 switch so i may have caused that. the lunge into 1st has gotten worse with a little bit of driving. so i'm thinking the external wiring harness is bad and i am going to replace that next.

I need some help finding a part number. I cant even find the part with a google search. a part number, supplier or even verbiage to help find the part through google would be very helpful.

Thanks!

Partsouq.com is your friend.

This is the answer.

You'll likely find it by searching "external harness transmission". Good luck!

And just so you have it ready, go ahead and look in to all speed sensors on the transmission and t case. I believe there are 2-3 in total? Should be referenced here as well.