I hope this is not an Evinrude shop. If so it is just another nail in the service quality coffin for Evinrude.
Evinrude service is absolutely pitiful these days.
But, yes, read the codes off the tach. Turn key to on, Systems Check tach goes thru it's self check light show, and then begins to flash the Check Engine light showing stored codes.
It bothers me tho....you have a Check Engine light AND SLOW? No such combination exists.
The codes that throw the Check Engine light DO NOT trigger SLOW.
So, are you sure you are actually in SLOW mode?
The only faults that trigger SLOW are:
Cylinder overheat code 14. The TEMP light only will light up.
Manifold overheat code 15. Same as above.
Over rev sensor. No code. Goes into SLOW mode tho.
Oil pressure switch/ no oil. No Code, SLOW activated.