There is a difference with California legal and Federal legal emission requirements. However if your 2011 Chevy Silverado is equipped with all the Federal required emission components which it was originally equipped with, (whether a catalytic converter was installed or not) it can pass the California smog check. The key is that the truck's emission system not be tampered with.
The rule is any USED vehicle which is equipped with the necessary Federal Emission Components is eligible for California registration as long as the vehicle's exhaust emissions fall within California's limits and the vehicle's emission system has not been tampered with. If it never came with a catalytic converter then a catalytic converter will not be required to pass the CA smog test.
