The device was left on Valois Avenue near Sainte Catherine Street. Police closed part of Sainte Catherine between Bourbonnière Avenue and Nicolet Street and evacuated nearby buildings as a precaution at about 5 a.m. Friday morning.
A police robot was used to approach and attempt to diffuse the device for several hours, before police determined that although the pressure cooker was made to look like a bomb, it was not in fact an explosive device, and posed no danger.
About 50 residents were forced out of their homes while the police carried out their operation.
Police have no suspects or motive, and say there is no indication that the car's owner was specifically targeted.
Pressure cookers were used as explosive devices during the deadly bombing of the Boston Marathon in April.