BMcEL

My automatic has been randomly shifting in/out of overdrive. It's been intermittent since I bought the truck in '04 and was a very rare occurrence until recently. I have searched and searched this site and others for a solution but no luck. I've also talked to a few local Yota heads who were previous owners of the A340H tranny and they ended up selling their rigs because of it (no idea why they didn't do a 5 speed swap). I have a feeling this is why the original owner traded mine in to the local Toy dealership where I bought it (second owner, yeehaw). Well, I finally decided to start troubleshooting, so the first thing I did was pull the engine coolant temp sensor (ECT) to test it in a pot of hot water with a temp probe and a multimeter. During removal, the connector fell off revealing this:




Obviously had issues. Bought a new one for about $40 (mid-price one from Napa) and tested it. Old vs. new (different testing temps but the old one is obviously out of spec).



There are other things that can cause this problem but so far this has fixed it for me. Hit me up if you have questions or need help locating the ECT. Oh and YOTATECH ROCKS!

BMcEL

Should look like this:



* Edit - fixed image.

BigSwole

I haven't drove my truck in so long I couldn't even tell you what overdrive drove like lol.

Subn to this for future ref. Thanks for the time to let us know.

rkonfire

BMCEL,

Interesting thread. I'm wondering if your situation and solution would apply to my '95 4Runner 3.0 AT. My 4Runner will take forever to reach normal engine operating temperature and kick into Overdrive if the climate control is set on cold.

I've noticed after starting my 4Runner when it's sat a while and has a low engine temp, it will only reach the normal engine operating temperature quickly when I set the climate control all the way to warm. However, when the climate control is set to cold, it will take forever to get the engine operating temperature to normal (and this is a problem because in order for the Overdrive to work, the engine operating temperature has to reach normal).

Thus, as a temporary workaround, I will leave the climate control on warm whenever the engine temp is cold, that way the engine temp will reach normal quickly and allow my Overdrive to kick-in (and yes, doing this in the summer really sucks). Once the OD finally kicks-in, that's when I can generally change my climate control to cold (or AC) and the engine will stay at normal operating temperature and run fine. However, sometimes even at this point while on the highway it will intermittently kick back out of OD if I revert the climate control back to cold (at which point I will then set the climate control back on warm and that will usually allow the truck to then kick back into OD).

Yes, the problem drives me nuts. Like you, CMCEL, I haven't seen people on this forum talk about this problem much either, except to say to replace the thermostat (which I've already done and it hasn't fixed the issue).

So, could you explain the process to replace the Engine Coolant Temp Sensor (ECT), and is this something that is pretty easily done?

Thanks CMCEL

-Chad

BMcEL

Green circle below is the engine coolant temperature sensor. Note that this view is from the back of the engine.


The engine coolant temp sensor can cause the transmission to kick in/out of overdrive at operating temp if it's out of spec. I'd recommend testing it referencing the chart in my original post. The throttle position sensor is part of this same circuit and can cause the same problem, so I'd recommend testing that as well. http://www.4crawler.com/4x4/CheapTri...ml#AliveOrDead

As far as the engine taking a while to heat up goes, the 3VZ seems to be kind of cold blooded, at least mine has been since I bought it in 2004. Not sure why running the heater is causing your engine to warm up faster...typically this has the opposite affect as the heater core dissipates heat from the coolant thus taking longer to reach operating temp. One theory is that the coolant loses enough heat when running through the heater core during the first few minutes that when it hits the thermostat it closes it, disabling the cooling system and allowing the engine to reach operating temperature faster. Based on the info you've provided, it sounds like your thermostat doesn't have a jiggle valve/air bypass hole and/or is a single stage thermostat. Here's some reading on that subject (it's about the 22RE but same concept):
http://www.4crawler.com/4x4/CheapTri...tml#Thermostat

I'd test the engine coolant temp and throttle position sensors first (relatively easy to do and you can then rule them out), and make sure you have an OEM two-stage thermostat from Toyota.

Hope this helps and let us know how it goes!

rkonfire

I actually enjoy when the engine rises to operating temp quicker when I set the climate control on warm because this allows my OD to kick-in sooner since my OD will only engage once the engine temp reaches normal.

My quandry is getting the engine to rise to operating temp quicker when the climate control is set on cold. Currently it takes forever, especially when I'm running the truck at higher RPMs. In fact, the longer I'm driving in a higher RPM range after a cold start, the longer it takes the engine temp to get to normal (isn't it supposed to be the other way around?).

I was looking at my 3.0 engine bay and was wondering if I need to unplug the coolant hoses that surround all the sensors. It would sure be nice to test these sensors without having to lose any coolant...

I appreciate your comments, bmcel...

BMcEL

You can test both the throttle position and engine coolant temp sensors in place, just unplug the connectors and buy (or solder your own) alligator clip leads for your meter.

BMcEL

UPDATE: Replacing the ECT worked great for a while, and it needed to be replaced, but the problem's back.

I know my throttle position sensor is bad, so I'll be replacing that next (needs to be replaced anyway, not just throwing parts at it).

rkonfire

Like my situation, my 4runner is weird like that too with the Engine Coolant Temp Sensor since the AT will only kick into OD once the engine is at normal operating temp.

BMcEL

Toyota engineered it that way. The transmission should not shift into overdrive before the engine reaches operating temperature. What's abnormal is the transmission randomly shifting in and out of overdrive AFTER reaching operating temp.

fork

mine did this before i traded it. however im trading for it BACK (uh oh the 3.0 again) so i'll probably be dealing with this again soon. hooray. ill have to remember to check this

rkonfire

Any updates?

RERunner

Any updates on what the problem was guys? I'm having a problem where it shifts in and out of OD when I'm on the highway. It won't go into OD until I reach normal temp, but then shifts in and out randomly while driving. I do notice that it has to do with the engine being warm.

1990 4Runner 3.0 V6 4WD

Thanks!

BMcEL

Haven't had time to replace my throttle position sensor yet...not 100% sure it's the problem but it needs to be replaced anyway so we'll see. I'll report back once I do.

BMcEL

Ordered my throttle position sensor finally...got the local dealership down to $103 on it. I'll install/adjust it this weekend and see how the trans reacts.

Mandy Tuning

i bet is tps,my 22rte/a340h was doing same thing until i replaced it with a used one from a 7mgte.

JamesD

Did you check the two transmission fluid temp sensors(NOT the temp switch that activated the light)? One is on the transfer case and the other is by the Park/neutral/gear selection switch.

James

BMcEL

That's next on my list if the TPS doesn't do the trick. From what I can tell, the only sensors that affect overdrive engagement are the coolant temp sensor, TPS, and ATF temp sensor, in order of influence.

JamesD

Well I would hit the trans temp sensor first. Personally I never had a TPS fail on me of all the Toyota's that I owned. If the TPS was bad, you would have other problems as well. Still you can be right and it may be the TPS but my hunch is on the transmission sensors and switches. Oh and another thing I forgot to mention, I had an 89 truck with the 340H and I had a problem with the reverse lights. Pulled the connector to the shift selector switch and it had corrosion so you may want to check that and all the sensors and the connectors. Post up what you find because my 89 had trans shifting issues as well but I never bothered to fix it and for years I drove it this way.

James

Mandy Tuning

there is no temp switch into the selector neutral/park switch. one is near the bell housing the other is in the transfer case,the transfer temp goes to the a/t temp warning computer,the temp switch in the bell housing goes into the tcm,then the tcm connect to the a/t temp warning computer that turn the a/t warning light.,about the selectors switch,both of them you can open them ,clean them cause they have a lot of gum,also remove the "wiper" copper contacts/spring, clean them and apply some dielectric grease.i do this to all a340h trans i have rebuilt,but i have seen more tps failure than you think,they get very sensitive at very light throttle causing voltage spikes that make the tcm think your pushing for instance the throttle more than it is.