Vehicle Code section 26521

Motor vehicles required to be equipped with power brakes and equipped with vacuum or vacuum-assisted brakes and motor vehicles used to tow vehicles equipped with vacuum brakes or vacuum-assisted brakes shall be equipped with either an audible or visible warning signal to indicate readily to the driver when the vacuum drops to eight inches of mercury and less. A vacuum gauge shall not be deemed to meet this requirement.
This section shall not apply to a two-axle motor truck operated singly nor to any motor vehicle manufactured prior to 1964.

Source: Section 26521, https://leginfo.­legislature.­ca.­gov/faces/codes_displaySection.­xhtml?lawCode=VEH§ionNum=26521.­ (updated Jan. 1, 1963; accessed Sep. 15, 2025).

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Verified:
Sep. 15, 2025

§ 26521's source at ca​.gov