code p1626 and p1631

please help sovle code p1626 & p1631 tahoe would not. what cause problem and how to correct.

You Didn't State What Year, Though For Year 1999-2001.

P-1626 Serial Data Communication Failure With Vehicle Theft Deterent Controller (no Password)

P-1631 Theft Deterent Password Incorrect

Sounds Like A Problem With The Anti Theft System...