Ford F150 - DTC Codes erasing?

Does anyone know how to erase the DTC codes for a 1991 F150 4.9 L without buying the scanner?

I tried disconecting the negative from the battery and pressing the brake for more than 5 seconds but it didn't work....

I get the 211 code and I guess the problem is fixed by I also guess I should clean the computer.

Thanks,

Read this thread.

Thanks, I delete the codes in the KOEO Test....I cannot delete the ones for the KOER....I just realize I have to do it with WOT ( More than 2000 RPM)....Tomorrow I will try again....
The codes remaining are : 311 & 538...

Rgds,
RH