A343f Shifting Issues

[Eggpattern]

Lately, the truck (kzj78) is having problems downshifting from lower speeds coming to a stop. Instead of downshifting, it will stay in a taller gear, maybe 3rd? You can then shift it into L and get moving again, then manually upshift into 2 or D and once up to speed. It seems od will also engage. This will last a few minutes and eventually the transmission will again begin upshifting and downshifting normally.

After some research, I've adjusted the throttle position cable a few times and the problem is still there.

Do you guys have any suggestions that can help me diagnose the problem? Ecu caps? Solenoids? Ect..

 

[GTSSportCoupe]

Lately, the truck (kzj78) is having problems downshifting from lower speeds coming to a stop. Instead of downshifting, it will stay in a taller gear, maybe 3rd? You can then shift it into L and get moving again, then manually upshift into 2 or D and once up to speed. It seems od will also engage. This will last a few minutes and eventually the transmission will again begin upshifting and downshifting normally.

After some research, I've adjusted the throttle position cable a few times and the problem is still there.

Do you guys have any suggestions that can help me diagnose the problem? Ecu caps? Solenoids? Ect..

When is the last time you've done a full ATF fluid flush? It's possible to do this yourself and save the money of using a shop. I can explain how if you like. I do mine once a year because I tow. Anyhow, new ATF can make a huge difference if your old ATF is completely worn out.

 

[Eggpattern]

I did a drain and fill last year. About a month ago, when these issues started, I again drained the old atf from the pan. Then I filled with new and flushed via the return hose 3 times and by the last time it was completely new fluid coming. Unfortunately it didn't solve the issue.

 

[kbushnz]

Typically the ECU cap leak issue can cause issues with the auto as its controlled from the same ecu as the engine.

 

[Agis4x4]

I have the same opinion but too am thinking that you hava a problem in a solenoid or accumulators. To replace solenoids is not very expensive and that work is easy.

 

[Eggpattern]

Typically the ECU cap leak issue can cause issues with the auto as its controlled from the same ecu as the engine.

Maybe I should start with checking the ecu then. I've never done this although I've been wanting to for some time.

 

[Eggpattern]

I have the same opinion but too am thinking that you have a problem in a solenoid or accumulators. To replace solenoids is not very expensive and that work is easy.

To me, from what I've read on this forum, the symptoms seem more similar to the ones guys have had with solenoids. I'm only guessing though and don't have the experience everyone else does here. If it turns out to be the solenoids, I won't be too disappointed. In looking for a set I found these

A340E A343F Transmission Master Solenoid Service Kit Toyota Lexus 1996-1999

According to the description the A340E and A343F solenoids are compatible. Can anyone help confirm this? If they do work, it seems this might be a cheaper option for me since they're coming from the US.

Toyota A340E A340F Transmission Solenoid Kit 2-Shift 1-Lock Up 3PC. Kit A340E-F

 

[Agis4x4]

Yes they are. In Japanparts.com you can check the reference of them. The filter is convenient to change too if you have the original still but if it's expensive now, you could wash it with dissolvent and after with air pressure. Remember to replace the ATF oil.

 

[Rukkh]

You may be able to tell whether its the ECU or the Solenoid by putting in a couple of diagnostic LED's or probing the ecu lines.

I just did this with lockup solenoid on my LJ8 a few weeks back and it seemed to work well.
I was seeing a real flickery signal on the LED over 90km/hr, which stabilised when i pulled the brake pedal back with my toe!

In your case you probably want to monitor the S1 and S2 wires, kbushnz has posted the pinouts here and elsewhere which is handy (if you have a kzj78, not so handy for my LJ78 but helped build the theory)
I tee-d off the SL line to an ~800ohm ballast resistor (12V system) which connected to my LED and then the LED to ground.

Watch the lights when the issue happens - if the lights look right, then its the solenoid, if the flickers or looks wrong then look at the ECU

 

[GTSSportCoupe]

I was seeing a real flickery signal on the LED over 90km/hr, which stabilised when i pulled the brake pedal back with my toe!

Could that be an adjustment or worn contact issue with the switch on the brake pedal? It's designed so that when you hit your brakes it takes it out of lock-up I think? Would explain your lock-up problems for sure!

 

[Eggpattern]

Thanks for the assistance everyone. I appreciate the input. Rukkh, that was a nice post on how to narrow it down between the ecu and solenoids. Although, it seems that at least the ecu needs some work. I pulled it today, after being away from home for a few days, and found a few melting caps.

I found a Lexus guy on another forum that had a pretty good write-up on replacing these caps. Basically, his points were that you could only order caps from 4 major Japanese companies; Rubycon, Panasonic, Nichicon, and Nippon Chemical. The caps must be rated 105C and low esr. Higher voltages seem okay, but I don't understand why as I'm already out of my depth. But, due to a lack of other options mechanic-wise, I'll follow his advice and be replacing some caps to the best of my abilities. Ordering, he says to stay away from eBay, Amazon, and the like and has himself ordered from Digi-key. Other trusted supplier websites are Mouser and Newark. Other than those sites there is a risk of getting fake caps.

This is the list of caps I found on my KZJ78, 9 caps in total:

1 bi-polar 50v (although in reading, someone has said this cap never goes bad)
3.3uF 50v
47uF 63v
33uF 35v
100uF 10v (x2)
220uF 50v
100uF 50v
220uF 10v

Anybody here with experience replacing these?

***EDIT***
Pay attention to certain cap "series" which have the characteristics we're looking for

Panasonic series EEU or FR
Rubycon series ZLH
Nippon Chemicon series KZH or KZE

 

[Eggpattern]

Since I'll have to get these sent to Uganda from the US, I'm thinking about using the shot-gun approach to this issue and ordering the solenoids too. Shipping cost make it so that adding on the solenoids makes sense. Has anyone ever dropped the pan to an A343F tranny in a Prado and had a good look at the solenoids? If so, can these be the right ones for me? Earlier, Agis4x4 confirmed that the p/n's match, but it seems like there are some variants to the A343F and A340E transmissions. The seller is very specific about them not fitting the "4 solenoid models".

Toyota A340E A340F Transmission Solenoid Kit 2-Shift 1-Lock Up 3PC. Kit A340E-F

 

[GTSSportCoupe]

Nice work finding those bad capacitors! I had opened my ECU a few years ago to check for this problem, but mine seemed ok. Maybe I should check again, and replace them preventatively.

I am an electronics technologist and have replaced many capacitors before. It's too bad you are not closer, or I'd do the job for you. It's pretty straightforward with the right tools.

I have had my auto trans oil pan off before, but did not pay any particular attention to the solenoids at the time. You could probably find pictures by searching google though. My understanding is that the A340 and A343F are very similar though, except for the tail end of it which has the transfer case for the F version. Maybe check ToyoDIY for part numbers crossing over?

 

[Eggpattern]

Nice work finding those bad capacitors! I had opened my ECU a few years ago to check for this problem, but mine seemed ok. Maybe I should check again, and replace them preventatively.

I am an electronics technologist and have replaced many capacitors before. It's too bad you are not closer, or I'd do the job for you. It's pretty straightforward with the right tools.

I have had my auto trans oil pan off before, but did not pay any particular attention to the solenoids at the time. You could probably find pictures by searching google though. My understanding is that the A340 and A343F are very similar though, except for the tail end of it which has the transfer case for the F version. Maybe check ToyoDIY for part numbers crossing over?

You're kind to offer your assistance. I've found a Surf picture, but haven't come across a Prado picture yet.

Between the solenoids and the ecu caps, I thought I might as well start with the easy ones first. Surf guys with 1kzte's make it seem that this is a must do mod, almost as much as cooling system maintenance. I never paid it much attention though. But there is a lot of information out there.

Since the problem is intermittent, I'm not sure that I could find anything by pulling the solenoids. Maybe extra resistance? I dunno. Again, if I can get a set cheap, I'd just like to buy them and be done with it. I just spent the last 3 hours trying to get my head around sorting through thousands of capacitors. I've edited the above post to help others. They cost around $3 for 8. I found all but the bi-polar cap. There was one but not the right temperature rating, which is apparently crucial.

 

[GTSSportCoupe]

Since the problem is intermittent, I'm not sure that I could find anything by pulling the solenoids. Maybe extra resistance? I dunno. Again, if I can get a set cheap, I'd just like to buy them and be done with it. I just spent the last 3 hours trying to get my head around sorting through thousands of capacitors. I've edited the above post to help others. They cost around $3 for 8. I found all but the bi-polar cap. There was one but not the right temperature rating, which is apparently crucial.

One way to narrow it down is just buy the Panasonic ones. I've never had one fail; quality seems to be top notch. But really all the made-in-Japan capacitors are pretty good. I don't think the bi-polar capacitors fail, so probably ok if you don't replace the one you cannot source.

 

[kbushnz]

When you replace the caps have a good look at the board and the tracks, the acid in the caps corrode and destroy the tracks....

 

[Eggpattern]

Something interesting happened today while driving. Again, the no-downshifting issue appeared. Only this time, the o/d off light was flashing. I drove it straight to a local garage to have the codes pulled. (My cel is not working for some reason but I assumed it was throwing a code). Two codes came up. One signaled the crankshaft position sensor and the other was the transmission speed output sensor. After getting home, I pulled the speed output sensor. I didn't see anything suspicious with the contacts.

Does this give anyone a better idea as to what exactly should be the problem?

 

[kbushnz]

Have you replaced the Caps yet.... As the ECU will throw all sorts of error codes while the caps are faulty.
Can get anything from shifting issues to the engine not running properly or at all....
While all the time the sensors are just fine...

 

[Eggpattern]

No, I haven't replaced the caps yet. I expect to receive them in about 3 more weeks.

 

[BurnsTACP]

I'm actually having the very same tranny issues. It would just jump around from gear to gear and in and out of OD sometimes. Also had the staying in a taller gear problem as well unless manually shifter to L. Was also having issues holding a charge. And had the truck just shut off on me while driving today. Had it towed to a shop, and the ECU is crapped out. The tranny fluid is also in a bad way. I just bought the vehicle recently so I'm getting to find lots of awesome easter eggs. The shop is looking into rebuilding the ECU, as well as flushing the trans.