P1631 GMC - 2003 gmc yukon xl

Question

NEED INFORMATION the check engine light came on after my gas cap was changed with an off brand cap with a lock on it. Engine wont start sometimes it will and won't start. when started it up after sitting black smoke came out when I started it up.

Answer 1

P1631 Theft deterent signal

If the vehicle doesn not start due to a fuel related issue or ignition related this can code up due to excessive cranking,You may not even have a P1631 (theft deterent signal) problem. The reason is when it did start up excessive black smoke, The theft deterent disables the fuel. Check the fuel pressure regulator with the key on engine off, disconnect the fuel pressure regulator vacuum line, cycle the key from to key on or key on engine cranking, if fuel comes out of the pressure regulator vacuum port this can be preventing the engine from starting .