A method for detecting faults in substring search operations using a processor unit including vector registers of M vector elements each. A non-limiting example of the method includes providing an M×M matrix of comparators for characterwise comparison of the elements of a reference string and a target string. A first zero detect vector having value indicative of terminating element of the target string and a second zero detect vector having a value indicative of terminating element of the reference string are generated. A resulting bit vector is generated using comparison performed by the M×M matrix. The resulting bit vector indicates characters of the target string that fully match the reference string and indicate characters of the target string that partially match the reference string. Fault detection in the substring search operations is performed by comparing the generated zero detect vectors with operands.