Authorities believe Jose Rodriguez kidnapped the boy last Tuesday.
Divers have spent several days searching the Delta-Mendota canal for the vehicle Rodriguez was last seen driving.
A farmworker had previously told investigators that they saw the car go into the canal just after the kidnapping.
Crews pulled 11 vehicles from the canal, in Patterson, over the past few days, but none were the silver Corolla the suspect was driving.
The sheriff now believes they've exhausted the capabilities of their dive operations.