2001 RX300 new/old remote entry keys won't stay programmed

[U.S. Lex]

I have two questions.

The first is "What's the difference between 'ADD' and 'REWRITE' modes, referring to programming a Lexus key?"

The second is "What might explain a vehicle's 'forgetting' a key which worked mere minutes before?"

I'm a new "old 2001 Lexus RX300" owner, acquiring the car from a friend.

He handed over two keys, one an original and the second a Denso replacement got from ebay seller, 1010keys.  Both start the vehicle.

He left the remote lock/unlock programming to me.

I found, a few, guides for how to do it (I mention "five lock/unlock cycles" for reference) and have successfully programmed both keys (a number of times).

It seems however that some thing is undoing/erasing the programming. After a time, typically shorter than one day, the vehicle stops responding to both keys, and has to be unlocked manually--WHICH, sad to say, SETS OFF THE SECURITY ALARM[1] (intentionally SHOUTING here)!

I first thought I had been doing it myself, unintentionally, by accidentally following a test sequence after programming of "lock/unlock/lock/unlock/lock" which results immediately in disabling both keys. However, my last test was to lock the car with the remote in the evening, unlock it with the remote in the morning, drive it, lock it manually with the switch on the driver door.  Returning later, the vehicle would not respond to the remote and had to be opened manually with the key WHICH, you guessed it, SET OFF THE SECURITY ALARM.

I've now found a variation on the programming sequence which I will try. The difference seems to be whether the door is CLOSED or OPEN when the key is inserted into the ignition.

[1] for those new to the situation, the solution is to put the key into the ignition, with HORNS BLARING, and turn it to the ON position to shut off the alarm. However, it will do it again the next time the car is unlocked manually, until the key is programmed--and you know, actually "remembered" by the car...

 

[U.S. Lex]

Re: the first question, I did find this, from which I quote (thanks, Colin):
 

Quote

 

There are 4 registration modes:

Add Mode:

Adds a transmitter without erasing existing transmitter codes. Four transmitter codes can be registered at one time. If [the] number of registered codes exceeds 4, previously registered codes are erased in order, starting with first registered code.

Rewrite Mode:

Erases all previously registered transmitter codes and reprogram new transmitters.

Confirmation Mode:

Informs user of number of existing transmitter codes already programmed in system.

Prohibition Mode:

Erases all existing registered transmitter codes and cancels wireless door lock operation. Use this function if transmitter is lost or stolen.

 

This answers my first question, and may answer my second in that it appears the registered transmitter codes may be being erased (Prohibition Mode) inadvertently.

It looks like trying to get into Confirmation Mode would be a good next step, followed by another attempt at programming, in Rewrite Mode if necessary.

[U.S. Lex]

And... I just had it to a locksmith who used a tablet computer (he called it an "Autel" and said it's what most use) to connect to the OBD port.   He first said it would not communicate with the vehicle.  After trying several things, he declared that none of them returned a successful message and that the problem was likely "a computer problem: either the computer is bad, or possibly, has already been replaced." (I don't actually see how the latter would explain not communicating...)

However, as an afterthought, he clicked the lock and unlock buttons on the keys. Both worked... and he wouldn't take any money because he said, "I didn't DO anything! Everything I tried did not respond!"

The problem remains that I don't know if this latest "fix" will last any longer than the earlier successes I've had.

If accidentally it does, be assured I'll track him down again and pay up.

...and probably bake him a cake.

I must say however that as a new "old Lexus" owner, I'm beginning to believe in spooks.

[U.S. Lex]

Back to report that, a day later, the vehicle had forgotten/erased/ignored the codes again.

Opening the door after unlocking the vehicle manually sets off the security alarm.

Thank you anyone for a suggestion.

[U.S. Lex]

The 2001 Lexus RX300 Owner's Manual says in a footnote (p. 15):

Quote

NOTE: *The alarm can be set not to sound. Ask your Lexus
dealer for details.

Does anyone know how to accomplish this?

Thank you.