lexusdog

iTrader: (1)

I recently purchased an 04 LS430 and I’ve had this happen to me on two occasions. When I start the car up in the morning in warm climate and drive it, it will go into some sort of safe mode and will not shift past third gear. I have tried to shift it manually through the gate but it still will not shift. If I come to a stoplight and shut it off and turn it back on it is perfectly fine.

To me this seems like something electronically because it will go a few hundred miles before the problem reoccurs. Not something that would be low fluid in my opinion. Anyone else have this issue? I searched but didn't find very much. Any help would be appreciated. Thanks

911LE

The trans is in fail safe mode. There is something wrong with it. Have a competent shop read the transmission codes and start there. Could be something as simple as a failing solenoid.

Galco

Same happened to my wife's 2004, wouldn't go beyond 3rh gear. Fail safe mode. After a great deal of searching didn't find much at all because these cars rarely have tyranny issues.

Solution was a transmission rebuild at local tranny shop. 3 years later running well. However as others suggested get a full diagnosis before committing to a bit pricey rebuild.

please keep us posted.

rkw77080

Lexus calls this "4th Gear Up-shift Prohibition Control". The main considerations are engine coolant temperature and vehicle speed according to the "Road Test" procedures.

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rkw77080

Replacing the engine coolant temperature sensor maybe your first step to try to resolve this issue. Please take a look at the link below...
https://www.clublexus.com/forums/ls-...re-sensor.html

lexusdog

iTrader: (1)

Thank you very much for posting that link and information. I just ran out and picked up a new coolant temp sensor. I will put it in later today and see if the problem pops up again. It has only happened are a cold startup where the engine temp gauge is still buried on low so this might be the cause. I will keep the thread updated. Thanks again.

YODAONE

2001 - 2003 LS430's use the A650-E 5 speed transmission which employs a fluid temperature sensor in the solenoid wiring harness.
2004-2006 LS430's use A761-E six speed.

If a fluid temperature sensor in A761-E, then perhaps a contributing factor.

DrAtomica

I have the same issue and I am also losing coolant, I wonder if that's the case since the shifting is fine until I start driving it a bit then gear 5 & 6 stop working.

lexusdog

iTrader: (1)

I would try to find your coolant leak first. Have your system pressurized.
My vehicle is actually not shifting past 3rd gear which is a fail safe mode. You can see if turning the car on and off makes it go back to normal. Will it shift through all the gears manually through the gate?

lexusdog

iTrader: (1)

That is a good point, I will look into that. I changed the coolant temp sensor yesterday evening, so I will see if the problem persists. From my research these coolant sensors start to go bad and send incorrect temperature readings to the ECU. Which in turn can cause a failsafe mode for the transmission.

rkw77080

ATF's viscosity varies slightly with temperature. The ATF temperature sensor is designed to compensate for this variation by adjusting the solenoids' shift points. A failed ATF temperature sensor will prohibit upshifting to the higher gears.

911LE

Before you waste more money throwing parts at the problem go have the codes read. Transmission codes are stored and don't illuminate the check engine light. I think most AAMCO locations will scan for free and have the ability to read the transmission codes.

lexusdog

iTrader: (1)

Just an update for future reference, my car still has the issue where it’s going into fail safe mode after replacing the coolant temp sensor. It did it this morning.
It looks like the ATF temp sensor would be an issue if you had an issue with 5th and 6th gear.

I'm going to have my codes read soon and will report back.

ls430w140

I ll highly suggest at this point to do a full health check with Techstream. It could be anything : VVTi solenoids, MAF, Line control solenoid, shift solenoid, low atf level, bad filters, issue in the throttle body area, low fuel pressure, issue with Evap or Fuel dampers... the worst case scenario - it could be ECM as well - not so uncommon in our cars.

You don’t want to replace each item obviously, but looking at Techstream data is a good first step to fix the problem.

lexusdog

iTrader: (1)

I will order that software and see what I can figure out. I did notice that the heat was not coming on after the car was completely warmed up so it could have a bad thermostat, which might be causing a problem. Im going to swap it out tomorrow and make sure the coolant level is correct.