My transmission is not shifting into overdrive I have a code reading of P1346.

The Check Engine Light is on? Did you read the DTCs.

The second link has the answer, the first link says it is a known issue. It is times like this you need the Dealership or a good auto electrician.

Transmission won't shift to third until temp rise

ClubLexus https://www.clublexus.com > forums > 713188-transm...
Apr 1, 2017 - Transmission won't shift to third until temp rise ... The solution is to drive slow and keep rpms at 2.5k and 3k at max till the engine and transmission warm up.
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Owner of Lexus RX300 with 182000 miles. Recently the ...

JustAnswer https://www.justanswer.com > lexus > 3wsxt-lexus-rx3...
Aug 22, 2010 - Recently the transmission won't go into overdrive. Stays in 3rd gear like when you press the o/d button to do so. When car is cold (live in ...
1 answer · Top answer: Hello and thank you for using just answer! The check engine light is on correct?

https://www.google.com/search?q=Lexus+RX300+will+shift+into+overdrive+once%2C+and+after+slowing+down+it+won%27t+go+past+3rd+gear

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to start with there is nothing wrong with the ransmission
It is all electronic faults
the transmission is constant mesh so ratios are not manually changed by done by servos and solenoids
the fault code refers to the TR sensor that can be changed out , the hard shifting is probably dirty oil and the changing between ratios a problem TCM or wiring harness connections
if the transmission oil has not been changed in the last 60K miles , that would be a good place to start, then have the auto transmission professional service center where you are having the oil change done, check out the servo/ solenoids operations

The short answer, yes. M46 models with the type J or P overdrive (depending on year and market) require a certain level of oil in the overdrive. Additionally, the overdrive is a lot like a standard automatic transmission with one gear range in theory of operation. Therefore, the hydraulic properties of said transmission do come into play here, line pressure, shifting pressure, accumulator and piston function all work together to engage or disengage the unit. Always ensure the unit is disengaged before downshifting and of course, shifting into low reverse.

Is your code reader capable of reading U, C, and B codes? The speedometer doesn't get it's speed reading from the wheel sensors. It gets it from the transmission. Not shifting past 2nd gear means your transmission is in "limp in" mode. It prevents shifting to avoid further damage. I see a transmission repair shop in your future.

overdrive servo/ solenoid is not operational , either from failed unit or wiring problem
check transmission actuator for operation or adjustment as well

Over Drive..... Generally speaking, overdrive (OD) is the highest gear in the transmission. Overdrive allows the engine to operate at a lower rpm for a given road speed. This allows the vehicle to achieve better fuel efficiency, and often quieter operation on the highway. When it is switched on, an automatic transmission can shift into overdrive mode after a certain speed is reached (usually 70+ km/h [43+ mph] depending on the load). When it is off, the automatic transmission shifting is limited to the lower gears. For an automatic transmission, it is almost always best to select overdrive and allow the transmission to control engagement of the overdrive. (It may be necessary to switch it off if the vehicle is being operated in a mountainous area or when towing a trailer.) With a manual transmission, overdrive should usually be selected when the average speed is above 70 km/h (approx. 43 mph).

Have the vehicle scanned.The overdrive light is like the check engine light for the transmission. There are transmission codes in the ecm if the overdrive light is blinking.

the flashing overdrive light indicates a code for the transmission you need to have your codes read to see what is causing the problem

There isn't anything wrong with your car. This is perfectly normal. I have a 2000 ES300 as well as other people that I know and it operates in the same way. Overdrive doesn't mean the same thing for every car or transmission. In our case overdrive is simply a reference to the top gear which is 4th gear. When you switch overdrive off(which is depressing the button causing the O/D OFF dash light to illuminate,) the highest gear becomes 3rd because you turned 4th gear or overdrive off. The application scenario for this is usually mountainous terrain where a lot of uphill driving makes it more feasible not to up shift into 4th gear while ascending and descending. It will not switch back to overdrive or 4th gear until you re-engage it by turning the overdrive back on or repressing the button. Again, when the O/D OFF dash light is illuminated, overdrive which is 4th gear is off and the highest gear will then become 3rd. It will never shift into 4th gear while this light is illuminated or overdrive is off. When you press the button and the O/D OFF dash light is NOT illuminated overdrive is on and therefore it will shift into 4th gear as usual. This applies to all 97-2001 ES300's and probably any other car you drive tat exhibits this same type of change when overdrive is turned off.

there is an sensor on the speed odmeter cable on the side of transmission. it will kill thr overdrive and cruise control but not the speedometer. about $50.fixed 2 explorers that way