How do i check the fuse number for the usb fuse for a citroen c4 1.6 vtr mk11 2012

The service and repair manual with diagram will give you all the knowledge you need to fix this or any other problem and you will get the manual from the given link https://toolsnyou.com

Try right of the ignition and down a bit

Hi Mbuelelo
There is a short and the fuse is protecting the wiring from burning.

Substitute fuse for a circuit breaker and / or place ammeter or clamp ammeter in circuit to monitor current draw and avoid replacing many fuses while diagnosing problem.
Then
Determine what devices that it powers and disconnect each till your meter current drops.

The USB in the radio. doesn't have a fuse. It's a problem in the radio.

What's the engine?

On this website you find fuse box diagram and description for Citrone C2


Citroen C2 2003 2009 fuse box diagram

95-100 foot lbs.

I have an idea these vehicles have independent fuses for left and right. so I would check the fuses.