Andhra Pradesh Police raided a petrol pump at Puttur road in Chittoor district and found that a fuel dispensing machine was tampered with using a microchip.
When physcially measured, the machine dispensed 40-ml less fuel per litre.
Police have taken the manager of the petrol pump into custody.
A case will be registered against the petrol pump owner, the manager and the person who sold the chip, police said.