AZRX300

I have a 1999 Lexus RX300 with AWD. I have a P1760 error code- Transmission line pressure control solenoid or solenoid SLT. The vehicle shifts extremely harsh from 1-2 and 2-3 and takes a very long time to complete the shift (about 3 seconds). Voltage coming out of the PCM was 11.45V last week and only 3.5 going into the solenoid harness connector. I rewired the PCM to the harness connector and it still on reads 3.5 volts at the harness... and now it reads the same coming from the computer. The solenoid makes a humming noise also. I am on my 3rd computer so i am hesitant to replace it... Any pointers? I need help.

Lexmex

Welcome to the Club.

I can't really tell you much more without being there, but with this code the SLT solenoid is inevitably the culprit and should be replaced.

If you measured the resistance between both terminals on the solenoid connector you should see a resistance of 5.0 - 5.6 Ω

AZRX300

The Solenoid Ohmed out and was fully functional when battery tested. When I back probed the Shift solenoid SLT connector at the PCM (E5-3) and got 11.45 volts. Yet was only getting 3.50 volts at the transmission wiring harness (just to the left of the range selector harness on the transmission.) So I rewired from the PCM to the harness connector. Shift quality only got worse and now i read only 3.5 volts from the PCM. Opened up the valve body and get the 3.5 volts across the board (that is to the Shift Solenoid SLT.) I have already put 3 computers in this vehicle and the solenoid works, my next course of action is to replace the engine wiring harness along with the transmission wiring harness and having this computer rebuilt, and yes reprogrammed. Any other suggestions on my next course of action?

Lexmex

It would be hard for me to help without being there. I'd literally have to check every single ground on the vehicle.

This code did jar my memory as the only time I remember such a code ever brought up to me (an I had to look on my old computer and its emails) was a case involving a friend in Mexico with a Rav4 they brought down that also used a U140 tranny. However, there was a case upon checking the fluid we discovered it wasn't clean (a little pinkish with a lot of accumulation in the pan). Cleaned it out with some drain and fills and all was well.

The harnesses would be the only other direct issue here that would affect this.

AZRX300

Thank you for your help lexmex, i really just needed to run my ideas by someone else because i too figured it would most likely be something in the harness. because the Shift Solenoid SLT circuit is rather straightforward... 16 gauge green and black wire runs from E5 pin 3 to pin two of the transmission internal harness connector- from there the wire becomes orange and runs into the solenoid connector. the ground is a light green goes up into pin 7 of the trans harness connector from their it grounds into the PCM and pin 2 of E5. I am most likely going to replace the harness with one from a 2000 rx300 w/AWD, not much was changed from '99 to '00 so i feel like the harness should be the exact same. I read in Transmission Digest that the Toyota Matrix and Pontiac Vibe- which used the U240 had many problems with this exact thing that the line pressure control solenoid (SLT) would stop working and the car would shift awful, and that the problem was the PCM needing to be reprogrammed or replaced- something i am going to do for the 4th time now. Thanks for the help though i will keep you posted.

grhi

Were you able to get this figured out? I am having the same problem on my RX300. Thanks.

AZRX300

I never did figure it out furthest I went was dropping the valve body but all the solenoids checked out. take it to a shop and have them reflash the ECM and check out the TCM harness. Be very careful with these computers they are very easy to fry with just static electricity

AZRX300

Ultimately I believe the vehicle had an open ground as there was never a full 12 volts on the circuit side

grhi

Thanks - I'll take some voltage readings and do some traces. (Unlike some other codes that don't show up for a while after being clear, this shows back up again immediately; which I think would make sense if there was an open ground.)