Per the link provided, it is clear to me:
Discussion: According to CVC Section 471, pickups are a motor truck by definition, which is required to stop at the scales per CVC Section 2813. However, all California weigh stations have signs stating: "No Pickups." So, if a vehicle meet the definition of pickup in CVC Section 471, it is not required to stop at the scales because of the signs stating: "No Pickups." If the pickup has a GVWR of 11,500 pounds or more, an unladen weight 8,001 pounds, not equipped with an open-box type bed not exceeding 9 feet in length, or the pickup bed has been removed and a utility body or flat bed has been mounted, then it no longer meets the definition of pickup in CVC Section 471; it is then a "motor truck" under CVC Section 410 and required to stop at the weigh stations.
PICKUP WITH CAMPER SHELL -- NO (May have to stop under certain conditions. Contact California Highway Patrol Commercial Vehicle Section for verification (916-843-3400))
Discussion: It can also display passenger vehicle plates, as long as the cargo in the bed is not being hauled for compensation.
PICKUP WITH CAB / CREW CAB WITH BOX-TYPE BED -- YES
Discussion: The utility or box bed has to enter weigh stations.
NOTE: I added the red to point out part of the text.
Wayne