There is a difference with California legal and Federal legal emission requirements. However if your Nissan Altima is equipped with the Federal required emission components (which it originally came with) it can pass the California smog check and register with the CA DMV.
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. This exemption does not apply to new vehicles.
