Failing to show proof of financial responsibility, meaning insurance coverage, is a violation of California Vehicle Code Section 16029. Violating this code could result in fines up to $500 plus penalties, impoundment of the vehicle and suspension of the driver's license. If the vehicle is impounded the owner will have to pay for all storage and tow charges as well.

The consequences can be far more serious if you are involved in an accident and do not have insurance. You may have to comply with the financial responsibility laws (SR22, SR22s, SR16) including having to pay for any injuries or damages from the accident out of your own pocket.

Being caught driving without car insurance is likely to cost you twice as much as what you would have spent for one year of auto insurance.

Comment Update:

These are the penalties and it doesn't appear to include jail time. The law states:

16029. Notwithstanding any other provision of law, a violation of subdivision (a) of Section 16028 is an infraction and shall be punished as follows:

(a) Upon a first conviction, by a fine of not less than one hundred dollars ($100) and not more than two hundred dollars ($200), plus penalty assessments.

(b) Upon a subsequent conviction, occurring within three years of a prior conviction, by a fine of not less than two hundred dollars ($200) and not more than five hundred dollars ($500), plus penalty assessments.

(c)

• (1) At the discretion of the court, for good cause, and in addition to the penalties specified in subdivisions (a) and (b), the court may order the impoundment of the vehicle for which the owner could not produce evidence of financial responsibility in violation of subdivision (a) of Section 16028.
• (2) A vehicle impounded pursuant to paragraph (1) shall be released to the legal owner of the vehicle or the legal owner's agent if all of the following conditions are met:
• (A) The legal owner is a motor vehicle dealer, bank, credit union, acceptance corporation, or other licensed financial institution legally operating in this state.
• (B) The legal owner or the legal owner's agent pays all towing and storage fees related to the seizure of the vehicle.
• (C) The legal owner or the legal owner's agent presents foreclosure documents or an affidavit of repossession for the vehicle.
• (3)
• (A) A legal owner or the legal owner's agent that obtains release of the vehicle pursuant to paragraph (2) shall not release the vehicle to the registered owner of the vehicle or any agents of the registered owner, unless the registered owner is a rental car agency, except upon presentation of evidence of financial responsibility, as defined in Section 16020, for the vehicle. The legal owner or the legal owner's agent shall make every reasonable effort to ensure that the evidence of financial responsibility that is presented is valid.
• (B) Prior to relinquishing the vehicle, the legal owner may require the registered owner to pay all towing and storage charges related to impoundment and any administrative charges authorized under Section 22850.5 that were incurred by the legal owner in connection with obtaining custody of the vehicle.
• (4) A vehicle impounded under paragraph (1) shall be released to a rental car agency if the agency is either the legal owner or the registered owner of the vehicle and the agency pays all towing and storage fees related to the seizure of the vehicle.
• (5) A vehicle impounded under paragraph (1) shall be released to the registered owner of the vehicle only upon presentation of evidence of financial responsibility, as defined in Section 16020, for that vehicle, and evidence that all towing and storage fees related to the seizure of the vehicle are paid. This paragraph does not apply to a person, entity, or agency who is entitled to release of a vehicle under paragraph (2) or (4) and is either:
• (A) The registered and the legal owner and is described in subparagraph (A) of paragraph (2).
• (B) The registered owner or legal owner and is described in paragraph (4).

(d) It is the intent of the Legislature that fines collected pursuant to this section be used to reduce the number of uninsured drivers and not be used to generate revenue for general purposes.

(e)

• (1) Except as provided in this subdivision, the court shall impose a fine that is greater than the minimum fine specified in subdivision (a) or (b), and may not reduce that fine to the minimum specified fine authorized under those provisions, unless the defendant has presented the court with evidence of financial responsibility, as defined in Section 16020, for the vehicle. In no event may the court impose a fine that is less than the minimum specified in subdivision (a) or (b), or impose a fine that exceeds the maximum specified fine authorized under those subdivisions. In addition to the fine authorized under subdivision (a) or (b), the court may issue an order directing the defendant to maintain insurance coverage satisfying the financial responsibility laws for at least one year from the date of the order.
• (2) Notwithstanding any other provision of law, the imposition of the fine required under subdivision (a) or (b) is mandatory upon conviction of a violation of subdivision (a) of Section 16028 and may not be waived, suspended, or reduced below the minimum fines, unless the court in its discretion reduces or waives the fine based on the defendant's ability to pay. The court may direct that the fine and penalty assessments be paid within a limited time or in installments on specified dates. The Legislature hereby declares that it is in the interest of justice that the minimum fines set forth in subdivisions (a) and (b) for these offenses be enforced by the court, as provided in this subdivision.