ES300doc

Lexus no overdrive until engine warm up.

I've owned several ES300's. I recently sold our beloved 1998 ES300 to my adult daughter because she was in need of reliable transportation. (at half the value by the way) This car did not have this feature.

I found a nice 1999 ES300 to fill the roll of my wife's daily driver. Apparently in 1999 Lexus decided it would be a good idea to lock out overdrive until the transmission temperature reached a certain level of warm. I have to assume that this was done solely for emission purposes at the time. I have read other opinions that it is to save the transmission, but I totally disagree. Running a cold engine at 3500 rpm to keep from getting overrun by traffic is not good and at that rpm would create more emissions to be expelled.

I live 3 blocks from the hi-way, so anytime I leave the house I have have to dive straight into 65 to 70 mph traffic. To deal with this we have to let the car sit and warm up. What a pain in the rear and a waste of fuel.

I have reached a point that I'm not willing to deal with it anymore and have been searching the internet for a solution. I found nothing other than it's a known aggravation and you just need to live with it. I did find that units for export to brazil did not have this feature wired to the ECM.

Solution, I've decided to install a potentiometer in the transmission fluid temperature circuit to fool the ECM , so that it sees a signal that the trans fluid is warm when it's really cold. We will see if this works.

If anyone has come up with another solution, I'd like to hear it.

Mythotical

That sounds like a solid solution! The world could use more free thinkers like us. Just don't flogg it until the engine warms up at least a little and you should have no problems.

ES300MM

Interesting idea. However I don't think you are suffering any engine wear to run it at 3500 on the highway cold. As long as you use a quality oil it should be fine. If the engine is not warmed up I would avoid going over 4,000 rpm or going more than 50% throttle. It's no so much the RPM's that build heat as it is the throttle position. Dumping lots of fuel into a cold engine can cause problems. Personally on mine I just drive it how it comes since that's the way it was engineered. If it was harmful to get on the highway when cold then it would have special instructions to warm it up first.

That said I don't think you will hurt anything by shifting into OD when the transmission is cold.

PFB

I'm not familiar with the actual technology of that switch, so here are my thoughts for what it's worth.

If that temperature sensor is a simple analog switch that strictly determines one set temperature, than its doable to connect a potentiometer and fool the ECU into thinking that the transmission fluid is warmer than it actually is.

If however, that same sensor (analog) also measures high transmision fluid temperatures, and sends the info to the ECU, than you may be looking for trouble. The reason I'm saying this is that lets say that by connecting a potentiometer you fool the system into thinking that it's 40 degrees warmer than it actually is, than when the fluid heats up to normal temperatures, the ECU may now think that the fluid is overheating. At the point the ECU may put you into limp home mode, cause eractic shifting, set a code, or may end up with some un intended consequences

If on the the hand, that switch transmitts a digital signal, than obviously you can not connect a potentiometer.

LeX2K

I think the system was designed to protect the transmission not the engine, so you may be doing harm to the transmission by tricking it into going into O/D sooner than it should.

Mythotical

It's analog and a few degrees won't hurt. It is designed to help the engine warm up faster that is all.

ES300doc

I included a bypass switch to manually return the circuit to stock as soon as the engine warmed up. I tried it out this morning and the test was a failure. Apparently the signal from the transmission temp sensor does not control the overdrive circuit.


It may be tied to the coolant temp circuit but I'm not going to mess with that bag of worms.

I might just tap straight into the transmission overdrive solenoid with a push button momentary switch that would release the signal as soon as you take your finger off the button. I have to think on it some more. I don't need to make it complicated or unsafe for the wife. It's just one of those things that bugs the **** out of me.

Thanks for the input guys, it's appreciated.

I did call my local Lexus dealer to see if there were any programming updates or secret programs and was assured that there was nothing available.

PFB

If nothing else, you don't give up which is good, however the Lexus engineers have put in this feature for a reason, that i dont think any of us fully understand, either the full rational for it, or the consequences of defeating it, so personally i would not try to bypass it.

However, I fully understand your reluctance to give up


Phil

Mythotical

I wonder if maybe you have a slow or bad coolant temperature sensor.

crwys

I have a 1999 lexus es300 and it always goes into overdrive when it's suppose to (around 35 or so) cold or not. So you definitely have a problem somewhere.

PFB

You live in California, so your fluid seldom gets cold enough for the overdrive delay feature to activate.

Below a predetermined certain fluid temperature, OD will not activate until the fluid heats up. This is how Lexus deigned it.

crwys

Ahhh I see, that is really interesting how a car will act differently in different areas.
Sorry.

geekrunner

HI, newbie here! I find this very interesting, and suspected that myself on our ES300. It always spun at 3000 rpm or more when cold and didn't shift to O/D till the temp gauge reached a certain mark. Thanks for sharing all your experiences and expertise!

ES300NZ

I think it's a few different things which control that system,
THW (engine water temp)
VTC - I forget what this is.
and throttle position. (I think).

.... so engine temperature that controls that system ?

Antony13

Mine waits 3-5 minutes to warm up before it shifts to O/D, if I warm it up as usual, 3-5 minutes, it operates like designed. Try having some oatmeal and warming up the car, it will do you both good. Or you could warm up your mate with 3-5 minutes of hugs and kisses while the car is warming up, it will do you both good. ; ) Either way, it is time well spent.