Question: 

The charging station does not change to error mode when I press the "CP Error" button on my EV-520 adapter. Is my adapter defective?

Answer: 

Most probably your EV-520 is not defective.
The CP Signal is the communication signal between the charging station and the electric vehicle.
By pressing the CP Error button, the EV-520 physically shorts the CP Signal to the ground connection.

If the charging station does not recognize this shortcut, it most certainly has a problem. In this case please always contact the manufacturer of the charging station.

If you are unsure or this behavior shows on every charging station you test, please turn your adapter in for a checkup.