P0449 GMC code is on

Question

I replaced the evap vent solenoid and the code never went away. What could this b

Answer 1

P0449 Evaporative emission (EVAP) vent solenoid control circuit

Yes it would be the ECM, this is more of a Cadillac problem when a P0449 occurs,and the ECM is the problem. The vent solenoid  is controled by the ECM driver circuit which is pulsed swtch on. if a any solenoid fails and is not repaired soon as possible it short out its driver circuit.