1997 taco 3.4 4wd overdrive not working

overdrive not working. Light button works for on/off. No check eng code. My trusted mech has stated he can tell the overdrive to be on w comp. he has tested all
circuits and can not determine why it will not shift. Mech is a solid transmission guy, owns shop. He has not seen an ecu ever crap out on a taco. He put out an email for a used ecu to consider. I did a trans filter change 3 weeks before this started. Ran solid as always. Does anyone have an odd ball evperience w this same issue? We've been thru all the normal nonsense. I'm going to disconnect battery to reset ecu and see what happens. thanks for any input, dave

 

It could be that I am misunderstanding the way you've worded the title of this thread but the overdrive is disabled when 4wd is engaged.

 

Right. two wheel drive is when it doesn't work. I put 4wd in title to reference drive train. Thx for response tho.

 

@gearcruncher

Could be a solenoid or valve in the transmission.

 

definitely not the solenoid. would the valve crap out and not get a eng light? my guy has rebuilt prob 10k trans. anything is possible I guess. Thx for input

 

When a transmission does " NOT " shift into overdive there are 3 things that need to be checked .
1 - have you checked for codes ? your trans is computer controlled . Try scanning your truck
2 - is the transmission temperature sensor functioning properly ? Needs to see proper trans and engine temp for OD to work
3 - The brake switch needs to be in the off position . Are you sure this is functioning properly
4 - The transmission computer needs to see that the transmission has upshifted to 3rd gear ( direct drive ) before the transmission will upshift into 4th

 

Do you mean the brake switch behind the brake pedal? My brake lights work, could it still be the switch? Thx

 

If your brake lights are functioning properly , chances are the brake switch is working as it should .
You need to scan your computer that controls the transmission . This is computer controlled transmissions 101 .
Auto-zone scans for free
Post back the results from the computer scan

 

I hear ya cruncher. Computer was scanned for trans and shows no codes. maybe trans temp sensor which I don't if is connected to comp. all of the comp "signals" are good, and mech checked all components of comp. I appreciate your time for input. battery disconnect didn't work either. frustrating man. will post next week when we figure it out.

 

oh yea, my mech has not charged me a dime yet. seriously he's about as good as you can get...thx again

 

OK , so no codes present after a computer scan .
The last time it worked was when you changed out the filter ? Did you overtighten the filter bolts accidently causing the overdrive shift valve to get sticky or stuck ?The valve body is made of alluminum and is very easy to warp if you overtighten the filter bolts
Did you do anything to the truck recently that may have prohibited overdrive from working ?
Keep in mind that the brake switch , temp sensor and 3rd gear switch need to be functioning as well as the speedometer in order for the transmission to grab overdrive .
My next step would be driving around with the scanner connected to see if the computer even commands overdrive .
If you can see the transmission computer commanding overdrive and no upshift into overdrive , you have a valve body issue
Whats your mileage ?
Here is some usefull info
https://www.tacomaworld.com/threads...sions-write-up-your-4-speed-automatic.325531/

 

hey cruncher
changed filter about 3-4 weeks before od stopped working. I snugged up the filter bolts pretty good but I don't think I overtightened to cause warp. I think the filter housing would have looked stressed if I did but that doesn't necessarily rule it out. The comp does command the trans to go into over drive when driving, my mech checked all those possibilities. he does valve body work at his shop unless it needs porting. I asked him about valve body but he didn't think that was causing it. He does work on my truck that I can't or won't do. he lets me supply parts if I want as well and he'll diagnose and let me do work if I want. I've done my brakes, fuel inj, throttle body and upper intake cleaning, valve cover gaskets, axle seals, rad fluid flush, blah blah. I don't drive more than a few miles a day on average. have 225k miles. nothing adverse recently or abuse. I will be following up w him next week. I also have a dam leak, very minor, at transfer case shaft seal which apparently need the xfer case removed to split open to replace. that and a valve body job would get costly. don't want to spend that money right now so hoping we can figure this out. will keep you posted. Thx for your time.

 

Over drive update. My tran guy can’t or doesn’t know how to check if cruise cont switch is affecting o/d. The cc does work when driving. Mech put out a email to borrow an eng comp but no luck. I’m down to looking at buying a used one on eBay or something at this point. dam this sucks....

 

If the computer shoes its commanding overdrive, I would the ECM is good.

 

Although, there has not been anything new on this thread in two years, I was wondering if you have figured out the problem. I am having the same one.

 

hello everyone . i just purchased a 1997 t100 2wd . and in am also having the the no overdrive issue. any update on this problem

i read the forum. on this.
my cruise control works fine
if shifts fine expect overdrive
the overdrive button works (lites up)
no leaks
no codes but i will go to autozone the make sure.
any help ... i will take..

 

Still no fix on the overdrive problem. Does your torque converter lock-up? Mine does not.