Hi Arthur. You clear the memory with the single erase or erase all functions.

Here is a detailed explanation of how you would read and erase a single code and what the circuit is doing. You momentarily press the circuit's read button causing it to ground the diagnostic socket for 3 seconds. The circuit then senses the pulses that are output at the socket and counts them. As the count increments it is shown on the LED display. When it is finished counting you may then press the erase button momentarily which causes the circuit to ground the diagnostic socket for 7 seconds.

The erase all function works the same as the above, only the automation is carried a step further. After just once momentarily pressing the read and erase buttons simultaneously the circuit automatically reads and erases all the codes one at a time by grounding the socket for 3 seconds, counting the pulses for the code, grounding the socket for 7 seconds, and repeating.

I first tried to do something like this 5 years ago using only electronic hardware. I remember posting somewhere about this and hearing from you back then. That design had limited success because electrically the pulses are not the same for all systems, and that circuit could work with some but not others. This new design with the microcontroller solves that problem, and because the functionality is implemented in software it's simple to have additional features like read or erase all codes.