355 ABS Light code 54

I got this car with this existing problem.The brakes work fine.
The ABS light comes on when the car reaches 30 MPH and resets when the key is turned off.
The local dealer has only a SD2 tester and can not link up with my 96 355
The dealer is not sure what the problem is.

I thought the Service/Workshop Manuals had the codes listed?

A code activated by vehicle speed would likely be a wheel speed sensor issue. "IF" it is a wheel speed sensor issue, which sounds likely (and is common) then the computer will retain braking, but turn off the ABS function.

Regards, JRV