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Transmission Keeps Dropping Into 1St Gear


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Hi all!
so my 92 SC400is having some major issue and I cant figure it out frown.gif

car starts and runs and drives perfect for the first couple miles. Then
no matter what gear or speed it seems like the transmission throws
itself into 1st gear. (RPM goes to 5k+, loss of power until i slow down
to 10mph or so) at this point it will drive but will not change gears
and will only go 10-15mph or so.

Heres the tricky part...a

If I shut the car off and wait 10 seconds I can turn the car on, put it
in drive and it shifts and drives fine for another few miles then does
the same thing. (I can repeat this for as long as I need to)


1. replacing ECU with a working one from a friends daily driver (same model and ecu part number) = same symptoms
2. No transmission error codes present,
3. CEL shows #13 RPM Signal no2 fail = could this be it?
4. checked fuids = all is fine
5. O/D on and off as well as "L" and "2" gear = same symptoms
6. reverse works at first then stops working when the tanny does its thing but works again after restarting car.

7. transmission clearly shows no codes (O/D light blinks every .5 seconds in diagnostic mode)

This is driving me insane! at first I thought it was the capacitor leak
issue, ruled that out i think. now the CEL #13 code makes me thing it
would make sense considering it has to do with my RPM. but then again
other people have that code and dont have my symptoms. There is a clear
cut recognisable pattern of symtoms to my issue, but no matter how much I
search or look I cant find anyone with a resolution or even an idea
what it is.....

any help would be greatly appreciated!

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Hey Ryan,

I'm going to take a long shot on this as I had a similar type of problem with my 1990 LS400 years ago. AND, I had the problem twice, each slightly differently yet both involving shifting. First off welcome, always great to have other owners to discuss stuff with about cars,

Snapped inside the left (driver's side) trunk hinge is a wire bundle. I had two of these wires break at different times. I guess Lexus was just a little short on the wires and the effect of opening and closing the trunk flexing wires and... you know.

Took me forever to unwrap all the tape the put around the wire bundle but I had beer while I was doing the unwrapping so it wasn't bad. When the first wire broke (white one I think) the car shifting became very erractic and wouldn't shift at all.

I know, it is a long shot but it is something that might be the problem. IF it is, (other than the unwrapping) it is easy to fix. I did leave the wires loose at the flex point but i wasn't too concerned about the little amount it shows.

Hope this is cause for hope.


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hey thank so much for the warm welcome! :)

i read about that on another forum but it looks like my trunk hinge is a solid tube and the wires are inside of it, its not the concave hinge arm where you can see the tube of wires... i can take a picture if that helps. im leaning toward some type of electrical issue, i just dont even know where to start looking other than folliwing the harness best i can from the ecu to each component.

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I understand. Guess it is a little different than the LS cars of the era. Yeah, I hate electrical issues. Just spent a bunch of time tracking down a blower motor issue in my Chevy truck. that stuff twists my back all up trying to parts out and the VOM leads in.

I have personally never heard of a Lexus RWD type transmission failing. Electrical issues take time and patience. I'm long on the first and short on the second. Good luck, I'm sure someone else will have other ideas.


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alright so i puled all the trunk carpet out and found the wiring harnesses on each side of the trunk. they are all wrapped and look fine, but like you said you had to unwrap it to find the break (im assuming it looked fine externally?) im going to do just as you reccomended and have a beer while i unwrap all the wiring and see if this is it. thank you for the suggestion, thats what made me look again. *fingers crossed*

At this point im almost hoping its the transmission, $200 and bolt a new one in....however I strongly believe its not the transmission...

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Good and bad news I guess. On the LS there is a wicked hinge point on the wires. Actually took me more than one to unwrap mine. Sorry to cause you extra work. I do know that vacuum also has some influence on a transmission. Really gotten tougher to diagnose problems with vehicles. I have toyota mechanic friends who take care of stuff like that on my cars.drop over to VB and I'll hook you up.

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no worries, i love learning anything new about my cars and do all the work myself (when applicable) what is VB?

ive been tracing the wiring from the ecu to the connectors all day and nothing so far :/ im going to buy a multimeter tonight hopefully and do the ripple test on my ecu which "should" find any faults in the wiring that cant be seen by the naked eye. if I end up having to replace this transmission just to find out its not the tranny i will lose it haha.

thanks so much for all the help so far VBdenny im running out of ideas here:(

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ahhh, never been. wih my car could make it lol. im in vegas, the sow rarely touches us.

ok so i was reading the toyota service manual for my transmission and it says you can diagnose the transmission very easily to seperate mechanical from electrical problems if theres not codes. it says just disconnect the connector for the solenoids in the rear of the transmission then use the gearshift to shift (D=1ST....2=3RD.....D=4TH) I can shift manually up and down by basically bypassing the shift solenoids. if the gears shift and hold while driving then its not a mechanical issue. and i can narrow it down to an electrical issue.

only one problem, I cant find the connector. lol anyone know which connector its talking about? of course theres no pictures.

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Having been under the LS400 which is the same drive train, I believe there is a connector on the transmission. Somewhere there must be a picture. Not very much fun tracking down such problems. I spent 10 hours to find a bad connector in my truck. Of course part of that time was in frustration which led to drinking and improper use of the English language.

Sorry you can't cruise over to the Beach. Enjoy your cold and snow.

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i believe I found it but of course its impossible to get to. i can fit my hand in there but can squeeze hard enough to get the clip off. ive got a buddy coming to help me later today so hopefully between us we can get it.

ugh i live in the desert for a reason. cold and snow are not my friend. LoL whats the weather like in VB?

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Virginia Beach is nasty right now. We alternate between pretty decent and terrible during the winter. Hardly ever any snow.

Working in tight spaces is a real challenge. Tore up my hands last week trying to remove a blower motor resistor from an impossibly small area.

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well maybe ill stay in vegas then lol. on th hands, yea people commonly ask me if im a fighter cause of all the scars on my knuckles lol. giving the connectores another shot tonight, and as you, i had some choice words while trying to get it disconnected lol.

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ok so i got the solenoid connector disconnected and the situation has improved drastically with some slight variations in the symptoms.

i can shift up and down all i want manually now. (my car basically a manual with no 2nd gear now)......I coult TOTALLY live with that except for one slight thing..... everytime i come to a stop and go (i.e. stop sign, red light, random kid in the road) it does it again, except now its more like neutral, i push the gas and it just goes nowhere even in high rpm no matter what gear im in. if I cycle the ignition and start the car it works imediatly.

I drove around for about 20 miles and it did the slip in 1st gear like before one time ( except this time i dont have to wait in between cycling the ignition, i can literally throw it in neutral cycle the ignition 1 time and start the car put it in gear and keep going all without even pulling over) ......CRAZY right?!??!?!

so now my question is the stop n go problem because one of the 4 disconnected solenoids is the lock up solenoid which i think has something to do with the torque converter?

or is maybe my issue the torque converter this whole time? ....... I feel like a freaking detective.. happy new year!!

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so after having the solenoids disconnected and reseting the ECU i dropped the ATF fluid from the pan and it was dark. (it was cherry red few days ago) i refilled with a couple quarts to replace the fluid in the pan and now it shifts PERFECT and has not got stuck in gear one time. maybe the filter? was thinking maybe its like the fual pump on my old camaro, everytime i would stop it would die, the screen on my fuel pump was clogged when i would stop it would jam it up and the car would die but start right back up.

grabbed a new filter and gasket, gonna replace it today and check the fluid color again.

(so far its more fun shifting my car manually without a clutch too lol)

Im sure this means my trans is gonna blow up in the next couple weeks, Im sourcing one locally for $200.... I will keep an eye on it and see what happens.

just wanted to update and put in a big thank you for the help!

any additional ideas would be appreciated of course lol

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