Remote Unlock Works
Driver Door Pushbutton Lock/Unlock Works
Keyhold Lock Works
Remote Lock DOES NOT work.

Can someone help diagnose what the problem could be? If the door lock actuator was suspect I feel I would not be able to lock it with the Door button either. Since the push button is working- what else could be wrong?

 

I am assuming you have the door closed and the window up when you are trying to lock it with the remote. There are safeties built into the system to keep you from locking your keys in the car. If ALL those safeties are satisfied, I can only assume the sensor in the lock/ latch assembly is telling the brain that NOT ALL of them are met, since it seems that all the other modes are functioning normally. It's trying to keep you from locking your key in, when the key is in your hand. Everything works from the inside because it knows you have to be there to operate them, thus can't lock your keys in and you out. The lock/ latch assembly is much more than just that, as it interacts with a lot of other things through the vehicle security module (computer). I must ask, are you CERTAIN the battery is good in the remote? That battery lasts a long time but it is a 3V battery and when it gets DOWN to around 3V it starts to cause problems, such as you are encountering. Most people aren't aware that ALL batteries have a voltage, when new, that is about 5-10% higher than rated. That means ALL, including your 12V car battery. I have had personal experience with failure beginning on car remotes when they reach the 3V or just barely under.

 

All windows etc are closed and I already replaced the battery with a brand new one (and from another Lexus's working key as well)

 

Some on here have theorized that the actuator is dying and since the remote only gives it a quick jolt it will not work, but it will work when you use the button on the door since you can hold the power on it longer. Not sure if that is true, but makes some sense to me.

Mine was doing the same thing and I was ready to piggy back the actuator, but I disconnected the battery to reboot just in case, and knock on wood, mine has been good for several month now.