YoFun

1996 4runner V6 Limited 4X4, ~270K will not shift into 4th.
Issue: When it 1st happened it fluttered back and forth from 4th to 3rd on the interstate at ~70mph, held 3rd for awhile and then shifted into 4th for the remainder of trip home (no CEL). The next day the transmission gave no issue (on the same to and from track to work ~50 miles); truck sat over the Thanksgiving holidays and the next time it was driven no OD, and hasn't returned (after several trips in it). Transmission shifts up/down fine, just will not go into OD and has no active CEL.

What's been done: Brought it to my local mechanic who got in the truck with me, we went on a test drive with a scanner plugged in. Though this wasn't a Toyota specific scanner, it is very high-end Snap-On. He was able to see that the ECM was not calling for 4th under no conditions, to test the solenoids he was able to simulate the ECM signal and manually shifted the transmission through all gears (1-4 ) both up and down (via the scanners diagnostic program). So this leads us to believe that there is nothing wrong with the transmission rather the fact that the ECM is not calling for 4th, now why is it not calling for 4th is the question.
Lastly, we used the scanner to verify that the ECM seen speed, temp, reverse, drive, low, 2nd, ECT PWR position; basically everything that could be viewed was seen to be working and responding. The O/D maintain button was used to during our testing with no change to gear commands, however we were not able to view its state in the ECM itself. This is something that I need to verify (ECM recognizing its state) but the dummy light in the cluster tracks, and if this was the issue the wire to the ECM would have to broken and then grounded on the ECM side (have my doubts about this).

The fluids are fine, and without going down the road of just spending money and changing parts how do I trouble shoot this further? The good news is the conditions aren't changing (its only a 3 speed now) the bad news is I'm at a lost for trouble shooting other than dropping it off somewhere. Trouble shooting recommendations would be great.

2ToyGuy

I'm certainly no professional on auto trans, being a manual kinda guy my whole life, but it sure SOUNDS to me as though the ECM has gone south on you. If all the inputs to it are good, but the output is bad, well...

Only other thing I can think of, is to pull the plug off the ECM, and check the signals it needs to control gear selection are all present, and in good shape. If you can't pull the plug and still get the signals you need to check, you can put the meter leads into the back of the plug while it's still plugged and see the signals as they arrive at the ECM.

Maybe it would be safer to jack up th rear axle till the tires are definitely clear of the ground, put it on jackstands, chock the front tires very well, and that way you can run the truck as though you were on the road, but you don't need to watch for other traffic, or whatever, and do your checking of the ECM more safely. That's what I'd do, personally. That way, you don't need a second person to assist you, and you can check the signals into the ECM right AT the ECM. If you need to, a short stick can reach the gas pedal so you try to "go" faster and faster, and check that the signals that tell the ECM to shift are present at the right time.

Good luck!
Pat☺

Malcolm99

That’s a tough one, I know the 99’ displays Trans temp and will not allow it to shift to 4th until it reaches 75*F, not sure if the 96-98 uses that feature or how/if that logic would be translated in the ECU. Are you running a trans cooler in line with the rad, every had the strawberry milkshake issue, what is your average temp outside locally, have you ever changed or tried to clean the steel mesh filter, do not use aftermarket filters in this trans, and what trans fluid is in it, it should be DEX III. Maybe check the ECU for water damage, it’s in a great spot if you have a windshield leak, and does your truck have an elocker and have you modified it for anytime use recently. Sounds like the OD button is depressed but it would be displayed on the dash I would think

YoFun

I have read where the ECM has went bad but that's a hard sale for me, could be possible though. I would love to have access to one, may search the local junkyards for a potential match. As for the signals to and from the ECM, that's the part of the puzzle I'm having a hard time tracking down (actual inputs and logic). In my head one of the inputs could be bad, as i used the ECM to shift gears via the scanner (or at least the outputs from the ECM). With just monitoring we never seen the ECM call for 4th, so I would really like to know what all has to be met to call for forth gear.

YoFun

I've owned this vehicle for a ~year, it does have the e-locker, no mods completely stock, have never changed the fluid and not sure if its ever been changed? I've seen reference to the milkshake, but only recently while searching forums for my problem. Temps around here can get pretty hot in the summers, but it just started cooling off when this happed 40-70 degF, as for the trans temp I know its got a temp sending unit b/c there's a high temp dummy light on the cluster, but not sure if its got a low temp setpoint too? Not suspect of water intrusion, had the kick panel off not to long ago and no signs of such.

There's no doubt that trans would love a little TLC but before I start performing this would love the mitigate my current issue. Would still perform a flush (or at least drain and fill) if there was some feedback that this solve the issue I'm having and nothing else was needed. Still trying to track down what the ECM wants to see prior to calling for 4th, and then checking these components.

Appreciated the review and comment none the less.

Malcolm99

If you don't know when the filter was changed(again aftermarket filters do not work on this truck), magnets cleaned and what fluid is in it, I would start there. It is common for this truck to have a rad failure and be flushed, rad replaced and passed on.

dropzone

iTrader: (6)

so no expert on autos but if the A340F is like the A340H in 2nd gen 4Runners there are some solenoids that you can replace by dropping the transmission pan.
I did it on my transmission in a morning, brought the shift points back to life. Not saying this is your root cause but worth checking into.

https://www.transmissionpartsdistrib...1-toyota-jeep/

YoFun

*UPPDATE*
So in my original post I didn't share that I've had rare issues with shift solenoid "B" and this was noticed by the CEL and skipping 3rd gear all together (shifting from 2 to 4th). When this happed it would throw code P0758, in the ~1year I've owned the truck this on happened 2-3 times. Since I lost O/D a week or two ago, I thought about the solenoids being an issue, but after the test preformed by the scanner and all solenoids responding correctly I felt like they could be ruled out. 2ToyGuy suggested a potential ECM issue, but I didn't put a lot of stock in that being the issue either, I still thought I was missing and input which was keeping the ECM from calling for 4th.

Yesterday I threw a code P1780 (neutral position switch), this was the 1st time I seen this code and the 1st code since my issue started. When I researched this code i found a potential cause being a bad ECM, this got me thinking.... code P0758 is the electrical malfunction of solenoid B, a weird code P1780 with a potential ECM being the cause , and the ECM not calling for 4th when everything I trouble shot looked good??

By chance I ran across an ECM on FaceSpace while looking at 4Runner parts and decided to give it a try. For what I got it for, I figured I could get my money back even if it didn't fix my problem. Well.... guess what, looks like I had a bad ECM. I did not have high hopes this was the fix, but it seems to have resolved the issue.

Thanks to those who responded to this thread and though I still do not recommend just going out there and buying parts, I attest that it can most certainly be an ECM that causes this issue and not sure how you would have came to this conclusion without just trying it?