My 99 RX300 master key works sporadically, but once it stops working, I can insert the key in the drivers door lock to manually lock the doors and then the key fob buttons will turn off the headlights & chirp the alarm to signal the doors locked. Other oddities are:
- While driving, the doors will lock/unlock on their own - just one or 2 times, not continually.
- Courtesy dome light comes on & will automatically dim before I start the car, BUT if I start the engine it will stay on for the entire ride, forcing me to manually turn off at the roof dome switch..
- Back hatch dome light no longer operates as it should in auto mode. Have to turn on/off manually.
- 6 CD changer in glove box (or something near there?) seems to be making a mechanical noise (like it's swapping CD's?) when the CD player is not being used.

* Tried disconnecting battery to clear memory
* Reprogrammed key every way I could find on the net (press gas pedal 5x, brake pedal 5x, lock/unlock door lock within 1 second of each other & perform all steps within 40 seconds...) and more, to no avail.
* Bought new BCM for area under ignition. Results were worsse than with the original & could not reprogram using one of 3 methods.

Any ideas?

 

I think I have an answer for you. The doors in your RX300 have 'position' sensors, which tell the ECU and alarm system if the door is in 'open' or 'closed' condition. If you have an open door, your remote will not lock the car. If you have an open door, the dome light will come on for a few minutes. If you have an open door and drive off, the RX will automatically try to lock all doors, then unlock when the system detects an open door. This is why your car locks / unlocks by itself when you start out. The faulty sensor has to be replaced. It is somewhere inside one of the doors.

Good luck, and let me know how it all works out!

Marty from Muggy South Florida.

 

Did you figure this out?