Thats not entirely true. If your car is equipped with an 8 pin diagnostic module near the battery you can read the codes from pin 6. Some 89 models had the 8 pin module other did not, I'm not sure when exactly MB made this standard.

__________________
Daily Driver: 02 E430 4MATIC
In the family: '03 E500 // '04 ML500 // 64 220SE