2001 Key Programming

The key programming instructions at Coastal Tech (http://www.coastaletech.com/keys.htm) are a good starting point. I've actually successfully programmed one key.

But a second one fails to program.

Here is some background information on my situation:

I bought my car used with only one master key.
I don't know how many master keys have been programmed for this car.
I successfully programmed one new master key, so at least 3 master keys have been programmed.
Another key fails to program, perhaps because I've reached the maximum.

I'd like to try starting over. The instructions at Coastal Tech say:

You can erase all the keys and start over by turning a working
master key 6 times and then opening and closing the door 7 times.
Then remove the key and reprogram again.

Has anyone tried this?

The statement "erase all keys" is confusing. If indeed, all keys are erased, would not the user then have zero master keys and be up sh!t creek ;-)

Coastal Tech also says that "You can have up to 4 masters". What happens if you try to program a 5th key? Nothing? Or does one of the previous keys get unprogrammed?

BTW - My e-mail to Coastal Tech went unanswered.