In California, there are penalties for driving without insurance no matter who the driver is. Therefore, if a California driver is driving someone else's car and gets pulled over for road violations, the driver would be responsible to pay the ticket.
The minimum fine for driving without insurance is $100 for the first attempt. If the person attempts to violate the vehicle code again, the fine will increase to anywhere between $900 - $2500 total.
Being fined for driving without insurance is only one of the possible penalties. Another way California has penalized people is by allowing police to have the choice to tow and impound an uninsured drivers car. Driving without insurance is considered a big deal in the state.
Why is driving a car without insurance so critical in California even if your borrowing someone else's car? It's due to the fact that if the person who is driving gets in an accident or is injured, the vehicle's owner could still be liable for damages.