1996 Limited v6 with auto trans 4x4 195,000 miles. Bone stock to my knowledge outside a transmission coolant.

Like the title says, Iv got a 1996 3rd gen 4runner that won’t shift into 4th until you let off the gas. As soon as you give it gas again it bounces back to 3rd. 1-3 shifts normally. Lock out works in 3rd from what I can tell.

trans fluid replaced 3 times over the course of 2 months to “flush” the system in the last summer.

oddities Iv noticed
If your turn overdrive off, it stays in third. You like OD on while in third it will jump to 4th then immediately back to 3rd. If you try it again with the button, it won’t shift to 4th, stays in 3rd but goes up 200rpm then drops back down to normal rpm for 3rd.

Scan tool shows no codes, speed sensor seems to be working.

TPS sensor never goes below 11.52%. Is this normal?

any thoughts?

thanks you!

 

On a different vehicle I would say your vacuum controlled shift actuator is bad, but I don't think this car has that.
Your mileage and description might suggest a failing lockup (O/D) clutch in the converter. It tries to lockup but the clutch is slipping so it backs off. Then again it could be the solenoid/valve for that. They aren't super difficult to remove and clean/test but you do have to drop the pan.

There is an outside chance it is maybe an intermittent or bad electrical connection controlling the O/D.
The FSM I have is 2002, but I have found it useful for a 1998 except maybe wire colors.
In the diagnostic pages DI-175 there are a few things listed for failure to shift from 3rd to O/D:

1) Something wrong with the ECM - ouch
2) 3-4 shift valve (I think one of the solenoids inside tranny)
3) O/D brake (I think maybe this is the lockup clutch inside torque converter)
4) O/D OFF indicator circuit
5) O/D main switch circuit

So you can always hope it is #5.

The O/D OFF indicator lamp is on the dash and the one wire circuit goes from the battery thru the alternator and AM1 fuses, the ignition SW, a 10A fuse in the driver side junction box and then to the lamp and the ECM E12.20 (green-yellow). The ECM controls the lamp. If the lamp goes on and off, the circuit is OK. I don't think this circuit could cause a shifting problem but it is listed as part of the things to check.

The O/D main SW is the button right on the shifter. Since it gets moved all the time it may have a bad SW or wire. The circuit is a single wire which goes from the ECM E12.14 (blue-white) to the button SW, and then (white-black) to a junction block in the center console and then to a connector and to ground. The wire colors may be different on your year but the circuit should be the same. The switch grounds the ECM terminal so as you press it, it should toggle between 0v and (5v or 12v). If you can find one of these wires in the center console you can trace it back to the proper ecm connector behind the glove box and probe the proper pin while wiggling and shifting even driving. If you give me a dropbox link or email I can send the pages if you don't have them.

Outside of these there is the vehicle speed sensor and throttle position sensor which you mention but I think they throw codes if bad. If the TPS goes continuous from approx 10% to 90% then its probably fine.

 

I don't have an automatic 4Runner, but I think the trans is old skoool enough to have a physical throttle position cable that goes to the transmission to alter the shift points. It's the cable that runs over the top of the intake manifold (missing on a manual trans).

The more that cable is pulled, the more likely the trans is to shift down, it's quicker to shift up the less the throttle opening. You might try adjusting that cable.

 

Good point. I had overlooked that possibility. A link with pics: https://www.toyota-4runner.org/3rd-g...own-cable.html

 

Thanks for the reply’s I check a bunch of connections ect over the weekend trying to eliminate the free “easy” stuff.

in anger on Saturday I gave it the beans and 4th started working for a bit. Let it sit Sunday and got in it to drive it to work Monday and it was back to being stupid.

I’m going to try the tv cable because it does shift into 4th when I let off in third. Which makes sense for the tv cable. My issue is it was working fine, then it immediately wasn’t. I feel like a cable out of adjustment would have been a slow decline. But I’ll loosen it up a touch and see what happens. Again thanks for the replies, I will respond with what I find by this weekend.

 

No go on the tv cable. Just affected shift firmness. I went in both directions, tight and loose.

Next step is wiring hunt down to see if those change what it does.

then shift solinoids.

 

Replaced oil, oil filter and shift solenoid. No change. I hesitate to try the ecm. But at this point idk what else it would be? Anyone have any additional thoughts?

 

So its either a failure of the ECU to sense the real vehicle state from: TPS, speed sensor, engine vacuum, bad electrical connection, or its from something that is really worn or broken like the converter clutch, low fluid pressure, or bad ECU.

Was there anything that happened or work you did on the truck shortly before the problem appeared?

I doubt the ECU could fail in that way since it does shift, but if you had access to one you could temporarily swap out to check then go for it. It is easier than dropping the tranny.

I assume you checked the shift linkage is OK. I don't know the symptoms of a bad neutral safety switch but it is another thing to check. Likewise with a bad AT temp sensor.

Automatics often have a port to check the fluid pressure. Might look into that although I would expect a low pressure to throw some kind of code, but not seeing a specific code for this though: https://www.troublecodes.net/toyotacodes/