No, that is incorrect. The chances that the light is due to an evaporative leak are about 1 in 100. The chances that your evaporative leak is the cap are about 1 in 20 maybe better.
There has to be at least a hundred different fault codes that will turn on the light. Each code has numerous logical possible causes and thousands of illogical causes.
To get the code read I hear Auto Zone will pull OBDII codes for free.
Bosch Master, ASE Master, L1
33 years MB technician