gp1200x

Anyone ever look into bypassing the cold temperature switch in the transmission for the warmup shift problem? I haven't reviewed the schematics yet but I am thinking of doing it. If it is just a thermal trip I am sure it can be bypassed. High temp switch should be another connection even if it is all in one device.
I am more concerned about wasting gas the the nuisance it causes as compared to any emissions. This really seems to be more of an engineering defect since changes were made in the later models.

ederny

gp,

This looks like one of those items that is controlled by the temp sensor on the engine. The problem seems to be the sensor signal goes to the ECM (engine control module) and is interperted in the electronics with the specific shift commands being sent to the transmission.

At first cut, it doesn't look like it would be easy, if at all possible, to alter this as it is now. Maybe an extra timing circuit to simulate a warmer engine for some "warm up period" feeding into the temp sensor circuit would help. I'll give it some further thought - it bugs me too!

salimshah

I missing something

The manufacturer's idea is to run higher rpm to quickly get to the right operating temprature. This done by not allowing user to get into high gear. A by product of higher rpm is that gear shifts are a litlle more bumpy. A bit of gentle driving generally raises the temprature to "normal" fairly quickly (by the time I get to freeway).

So do you want to extend the time for engine warm up by going to higher gear early? (bad for emission)
or
Avoid the lurching/bumping at low temprature? [can be reduced but not eliminated by less gas pedal action]

Salim

ederny

What I don't like is the fact that I am forced to drive slowly or rev the engine 3-4k RPM when cold. I can't run a cold engine at that RPM - guess I am from the old school, and I don't like pulling out on the 2 lane from the drive way when every one is going 45 and I'm screaming along at 25 MPH. I do it but don't like it.

In other words, I am very happy to warm up the engine at high rev, I just need higher road speed to go with the high revs - nothing wrong with that!

toyo

That system is there for a reason. It is thier for your transmission. The tranny fluid is not a good lubricating agent when cold. The bands, etc need good lubrication so they dont improperly wear. I would just live with it. Let the motor warm up for about 2 minutes, then drive off easy till warm.

ederny

...but, no other vehicle I've driven (with transmissions & transmission fluid) operates like this! Don't you think it could have been done just to pass emissions in Calif?

toyo

Yea, and nobody has the reliability and long term dependability that Toyota has. Honda has the same setup for the transmission.

gp1200x

Emissions is the last of my concerns. I have owned dozens of cars and trucks and none have ever exhibited this type of excessive warm-up shifting condition. The other cars we have owned are just as good and expensive as this RX and we put more than 150K on many of them without ever having tranny problems. I don't believe the RX tranny is superior to other trannys. My other cars, and all the cars of my family members, all shift into high gear well before the temp ever reaches normal operating specs. This condition happens even when the tranny oil is at 50 degrees which would not cause excessive wear. I still believe this problem was created by Lexus engineers in an attempt to compensate for another condition such as satisfying emission standards. I would rather have the tranny shift into high gear, drop the rpm and enginge noise, and take a little more time to reach normal op temps. After all this is exactly what they did in the later production models.

salimshah

my 2cents ... [Not trying to convince any one out there]

The lube issues are old (outdated) with the multigrade lubricants. The only lube issue is collection in pan vs in-circulation and this one gets taken care of in first 3-7seconds after the vehicle is turned over.

I really think it is an emission issue .... getting to normal/optimum conditions and getting there quickly. [Just running the engine to warm up simply slows down the process]. Partial soloution was to up the idle speed when cold, but this becomes a non-issue when driving .... foot on the gas pedal ... no longer idling. The nifty (gp1200x disagrees) solution is to force the tranny to stay in low gear till the engine warms up and also the catalytic convertor starts glowing. The driver is expected not to stress the engine till atleast the temp gauge shows some life.

My guess is that this helped RX get Ultra low emission rating. Tampring with it may break some state laws (no intent to sermon) and fail emission test.

Salim.

ederny

Any states check emissions at cold start? Mine (Mass) does not - only tests warm at speed (ramp up and ramp down on a dyno - twice!).

So drivers who have these vehicles that don't shift, run the risk of revving the engine when it (the engine) is cold. To me that is worse than any cold tranny issue. Just think of the valves (valve guides and cams) and piston bearings and rings with sluggish oil (right , multiviscosity is good). Pulling into traffic at the evening rush hour after sitting out in 20 deg weather all day I'm pushing 3000RPM - it just kills me. Ok, I'll be good and try being more patient, sit in the cold waiting for the engine to warm before driving home...

gp1200x

I spent some time and looked into it since this problem really bothers me. I am assuming that the reason that the vehicle does not shift into OD is because of the AT sensor readings and not the engine sensors. I haven’t seem any proof of this so it is an assumption I made based on the connections to the ECU. Hopefully this is correct or else everything below is invalid.

I pulled the schematics from Mitchell and AllData and found that there is a single AT sensor that provides input to the ECM. There appears to be four conditions that the ECM can sense. The AT sensor appears to be a variable resistor (bimetallic) that has a high resistance when the temperature is cold (greater than 3.5K ohms but less than 156K ohms) and a very low resistance when the fluid temperature is abnormally high (231-263 degrees F).

Conditions 1 and 2 – If the sensor is shorted (less than 79 ohms) or open (greater than 156K ohms after 15 minutes of run time) a DTC code is registered and the instrumental panel MIL check light probably comes on.
Condition 3 – if the AT fluid temperature is cold an ECM condition may be set which prevents the OD shifting. (I assume that this is when the tranny fluid temperature is less than 77 degrees F - more than 3.5K ohms)
Condition 4 – If the temperature is above 77 degrees but less than 230 degrees than the ECM may be registering a condition which allows for OD shifting. Normal operating temperature is 158-176 degrees however I do not know what the ohm setting is at this temperature….(too lazy to go through the trouble). I assume it is between 3.5K and 263 ohms.

What I am going to try to do is to insert an adjustable time delay circuit between the ECM and the AT sensor to fake the ECM into thinking that the tranny temp is slightly warmer than 77 degrees for the first 640 seconds. Then the delay circuit will end and normal connections between the ECM and the sensor will be re-established. This may sound like a lot of work but after 2 hours of thought and half an hour at two stores I had what I needed.
Total cost was $25 including cable dressing and small plastic box to house everything.
The time delay circuit box was found at a junk store for $5. I used trailer wiring with the four wire end plugs for the new connections so that it would be water tight.

If anyone has other ideas or knows this will not fix the problem let me now. I may try it this weekend if weather permits. Freezing rain again in NY.

Below is the info I used to determine this. Last picture is the circuit I made.

ederny

There are a couple of things we should check out.

First, I am certian that at cold temps, the tranny does not shift out of 2nd gear. I'm talking about those 10 deg mornings. I'm sure you have had a few there in NY. Let's say 20 mph at 2500rpm. So, I'm thinking this is not an overdrive issue.

second, the tranny always shifts to 3rd at the same point on the eng temp guage (half way between the first mark and the second). Now, the most interesting fact I've observed is that the eng shifts out of 2nd gear at the same time the blower comes on for the heating system. Sounds like the eng temp sender is involved here. I hope to check this out soon. Maybe we need the time delay on the eng temp sender!

gp1200x

?? I don't if mine is acting in that same exact fashion. I will try a few things tonight once it drops below 30. I never noticed mine staying in second. Mine will shift through three gears but not the fourth (OD?) . I assumed it was OD but I will retest tonight. I though that I had pushed the OD button and no gear changes took place so I assumed it was not going into OD. I will test to see if it is really using first, second and OD but no third.
You could be right in that engine temp also plays a role. I have noticed that mine doesn't always shift at the same exact temp location so it is hard to tell. I may need two delay circuits as you suggested though. I wish there was some write-up somewhere about this and how it is controlled. Hopefully tranny temp and engine temp would be the only things setting the conditions. Too bad I don't have a tranny dipstick warmer to use for a test. I have the schematics for all the wiring but the writeups are really lacking. For all I know it may be possible that the ECM can be programmable to stop this condition.

ederny

gp,

I took the RX out early before sunrise at about 28 deg. Sure enough, it was in 2nd gear until it warmed up. I shifted between 3rd w/od and 2nd gear to make sure. It was running at 2500 rpm and 28mph. I'm planning on checking out the eng temp sender and the signals at cold vs hot.

gp1200x

Took mine out at 37 degrees. At 2500 rpm mine was hitting 38mph. Once it warmed up I tried to figure out what gear I was in but I could not hit that combination in any gear with or without OO. I also noticed that when it is warmed up if I place the car in 2nd gear it will never go into OD, since turning off OD does not cause any changes. Therefore I think at cold temperatures mine actually goes into first and second and may be going into OD to hit the 2500/38mph combo.

I may buy the second delay timer and have it ready to hook up for the engine temp fakeout since it doesn't add that much complexity to the setup. I'm just not sure what sensor it is actually using now.