Mercedes-Benz C-Class
2001–2007

Illustrative — for orientation only.

Location

LHD (every US car): driver's footwell, under the lower edge of the dashboard to the left of the steering column, directly above the pedals and immediately beside the bonnet (hood) release handle — find the hood release first and the socket is just to its right. Sit in the seat and look up under the dash at knee height. Same position on the saloon, the wagon and the Sport Coupé, on every engine, and it did not move at the MY2005 facelift. There is no 38-pin round diagnostic socket on the 203; the 16-pin OBD socket is the one every key tool and the dealer system use.

How to access

The socket sits behind a small flip-down plastic cover. Hook a fingernail under its lower edge and pull it down towards you — no tools, and don't lever it with a screwdriver because the hinge snaps. The 16-pin connector is visible straight away. On a lot of high-mileage cars the flap is already missing. If the tool gets no power, check the fuse feeding the diagnostic socket in the driver's-side dash-end fuse box (open the driver's door, the cover is on the end of the dash). On US 203s the socket is reported sharing a fuse with the brake lights and ESP/ABS circuits, and at least one US owner found the dead socket on the transmission fuse instead, so read the fuse chart in the lid rather than trusting a forum number.