stockgreen93runner

Alright, so I have a 93 4Runner SR5 V6 3.0 automatic. Whenever I try to get up to highway speeds when the car is relatively cold, it will not shift into overdrive. This doesn't just happen sometimes, it happens every time after my car has sat for a long while. The temperature gauge has to reach halfway before it will shift into overdrive. Also, when I go down large grades or hills for a good distance, the engine cools off too much and overdrive becomes basically unavailable and I'm stuck in fourth gear. I asked the guys at a Toyota dealership about it, but they were absolutely clueless. Anyone have any clues why this might happen or the fixes to it? I've been dealing with it for several years since I got the car.

mt_goat

The tranny computer (ECU) is programed to not allow use of OD when the coolant temp is too low.

So, it could be
(1) Normal
(2) Your coolant temp is too cool (like the t-stat is stuck open or the fan clutch is locking up too much.
(3) Your coolant temp sensor is reading wrong

stockgreen93runner

Thanks for the info. I'll for sure have that looked at.

DPut87

Ok, first post here on YT, so hold your tongues a bit.
I have the same issues that he is having, for the past month it has been not shifting into overdrive. I keep getting mechanics telling me that it's designed that way.
Problem I have with that is that this month has been warmer than lasts and it never had the problem before 2 weeks ago. I have heard that the Coolant Temp. Sensor can be the problem but can someone who knows tell me what the "proper" temperature it should read to engage OD?

Flash319

I am pretty sure it is 70F.

DPut87

Sounds great, I have been trying everything, the thermostat is fine, solenoids fire right, and everything else seems to be in place. I am going to try and check it tomorrow, I have read of there being crystallization in the passageway that the sensor is in. Would I need to remove the entire unit to tell or is there another way(its a v6 with the intake in the way).

Thanks

Bigblock

A thread thief!
Bigblock

toyota4x4907

I think SOMEONE needs to read the forum rules
Says its better to post in an old thread than to start a new one, as long as the questions pertain to each other

hehe

But THEY also need to search, which is a rule as well.....

DPut87

Thanks, I did read the rules and when this thread fit the bill I continued it on for further information, as to allow further searchers to find more information in one place.
When I searched I read through several threads about the OD problem but did not come across anything definitive relating to temperature.

As for results. I checked it this morning and there was buildup on the sensor(red coolant crystals) which makes sense that they would keep the sensor from reading accurately. Cleaned it and the problem is fixed.

Thanks for the info guys, on to bigger and better things.(lifts and a new rear bumper)

91diesel

was your tranny shifting like the ECT power button was pressed also? My transmission won't shift into overdrive and it has the higher shift points like the ECT is pressed. It just started doing this today. A340/343F, I tried changing the temp sensor for the computer but no luck with that helping the problem.

DPut87

I'm going to have to regetibly say, mine is doing the same thing again. And no it is not due to cold weather, it has been in the 75's + and according to Toyota the switch that holds OD off when cold onyl acts under 60 ambient temp.
SO the quest continues for an answer, which I may have from a man up north in WA. He has a few ideas that I will be trying out when I am home from school this summer.
(as a note) I am overhauling the whole thing seeing as it has 195XXX on it now, about 2000+ miles a month by me)

91diesel

could it be your sensor is still faulty? All you did was clean it off, maybe it wasn't working real well anyway.

GSGALLANT

The A340H transmission will not shift to O/D and the torque converter will not lock up until the engine coolant temp reaches 70 deg C (158 deg F). It has nothing to do with ambient temperature, except that the lower the ambient temperature, the longer it will take the coolant to warm up.

DPut87

I would say "oh that explains it" BUT, according to Toyota and MY own experience, this issue was never a problem before.
That means that in the winter months(when it would be more pronounced) I never had the problem. Then, one day it happened, then a few days later it did it again, after a few more times it happens every time.*and my driving has not changed as it is still only 200 ft to the highway for me.*
Also, I previously noted that it would engage OD/lockup at around 75 deg F.
I did replace the sensor, no dice. Checked most of the wiring but I can't tell if the resistance has become too much for it? The fun part is that a friend has the same 4runner 95 limited and does not have the issue, even side by side he gets OD long before me and about the point I used to.


*as a side note* Can someone show me the Toyota Manuel that says this 70 deg c thing? The guys at 2 different tranny shops and Toyota have never heard of this before? All the other answers were "I read it online"