Intermittently lose 5th gear in A750f auto transmission gets stuck in 4th

[Jimmyjopulsen Lurker Find all posts View Profile Close Jimmyjopulsen]

I’m stumped on this and can not for the life of me find a solution on any forum for this issue.

my 150 Prado intermittently loses 5th gear. I have to stop on the side of the road, turn the car off, wait 10 seconds and the start the car back up and I’ll have 5th back. I’ve serviced the transmission, yes used the correct fluid and got it to the right fill level/temp. I decided to service the transmission when the car started doing this. Hoping it might resolve the issue, no luck. I’ve tested the resistance of all the solenoids on the valve body and they’re all in spec. I’m not getting any codes on a scan tool either. I’ve fitted a trans cooler in hopes that might resolve it as I feel like it does this only after being driven for a while, no luck.

if anyone has had a similar thing happen and has a solution for this I’d be very happy to hear what it was as this is driving me insane.

[ptommo59 Senior Member Find all posts View Profile Close ptommo59]

Hi Jimmy,

I'm no auto trans expert but have you checked the ATF Temp #1 (Pan) Temperature Sensor reading when you are having the issue.

Overdrive and Lockup are inhibited until the ATF Temp #1 reading gets up to normal operating range (I think it's about 60 deg C) and also if the sensor is faulty.

Worth a look.

[ptommo59 Senior Member Find all posts View Profile Close ptommo59]

Hi Jimmy,

Also did a quick search online for you and these FJCruiser links may be useful as the model listed used the same A750F transmission.

The first link has a troubleshooting guide that has a section on No up-shift (4th to 5th). The second has various sections of the repair manuals which may have the info on faultfinding each issue in the list but I haven't checked which ones

https://www.purefjcruiser.com/docs/2...tem/017006.pdf

Technical Documentation : Pure FJ Cruiser, Parts and Accessories for your Toyota FJ Cruiser

[krypto Avid PP Poster! Find all posts View Profile Close krypto]

Hi Jimmy,

Also did a quick search online for you and these FJCruiser links may be useful as the model listed used the same A750F transmission.

The first link has a troubleshooting guide that has a section on No up-shift (4th to 5th). The second has various sections of the repair manuals which may have the info on faultfinding each issue in the list but I haven't checked which ones

https://www.purefjcruiser.com/docs/2...tem/017006.pdf

Technical Documentation : Pure FJ Cruiser, Parts and Accessories for your Toyota FJ Cruiser

Great info, very specific!

[carco Advanced Member Find all posts View Profile Close carco]

Mine does that every so often. Most common when starting off downhill, car is not working hard and decides to stay just in 4th.
Some owners have had to pull over, turn off and restart in order to get top gear. Mine will eventually change into top.
From previous posts from those owners, if you have the EGR turned off in the ecu, you’ll experience this phenonium every so often.
This seems the only common theme.
Mine has reflashed ecu with EGR turned off.

[ptommo59 Senior Member Find all posts View Profile Close ptommo59]

If you have modified the EGR and have no other faults the Engine/ECT ECU may be using the gearbox to manage higher than expected EGT's.

As the EGR when open reduces combustion temps and EGTs go up under load in higher gears. High EGTs = Higher NOx levels so bad in the pollution gods world.

So it would make sense if it thinks the EGR valve is fully open that its next step in managing the NOx levels would be to drop a gear or lock out overdrive to reduce the EGT temps.

Your downhill low load trigger could also be consistent as the EGR valve would be expected to almost be fully open under those conditions similar to idle.

Make sense but its only a guess on my part. You may be able to verify or disprove this if you have a scangauge or torque and monitor your EGTs to see if they are greater than normal when you start experiencing the 5th lock out.

This link has a good explanation of the EGR system if you are interested The basics of EGRs - what they do, how they work, how to troubleshoot | Delphi Auto Parts