Mercedes-Benz C-Class: Fuse Diagrams and Commonly Blown Fuses
Locate your fuse boxes, and become current with fuse sizes as well as color codes. Conduct fuse testing to find blown fuses. Gain the capacity to replace your fuses, and the potential to insulate yourself from shocking repair bills. This article will help you understand the fuses in your Mercedes-Benz C-Class w204.
This article applies to the Mercedes Benz C-Class w204 (2007-2014).
Sunroof, seat heaters, wipers, sound system, lights are all of the electrical features of your car, which are powered with electricity made by the alternator and stored in the battery. Power supply wires from the positive battery terminal conduct electrical current to each component, and each component is then bonded to the chassis by a short length of grounding wire that is screwed into the frame nearby. To complete the electrical circuit, the entire chassis serves as the return path to the battery, and is connected to the negative battery terminal by a short length of thick ground wire in the engine compartment.
Each power supply wire is controlled by a switch and a fuse. The fuse is designed to carry no more than the normal current on that circuit:
- In normal use, the fuse is intact. The current flows through the full circuit, and you use the switch to turn on or off the component. See Figure 1.
- When faulted, the fault allows too much current to flow through a shortened circuit, creating excess heat and melting the thin connector inside the fuse. The fuse "blows," and shuts off current much faster than you can turn off the switch. See Figure 2.
- Some faults can happen inside the component. The wiring may be fine, but bad connections in a window motor or control board may cause the short circuit and a blown fuse.
- In older cars, the power wire itself may work loose and chafe on the chassis. The wire insulation wears off, and the bare wire contacts the chassis, completing the short circuit back to the battery and blowing the fuse. Because the wire is loose, this short circuit can come and go.
The Automotive Fuse
The electric current that a component uses is measured in amperes (amps for short). Your wiper motor does more work and uses more amps than the tire pressure monitor. So the wiper motor needs a 30 amp fuse, while the tire pressure monitor uses only a 5 amp fuse. In both cases, in the event of a short circuit the properly rated fuse will blow. Always use the proper fuse.
Auto fuses are marked and color coded (Figure 3). The two common sizes (regular ATC and mini ATM) are available at auto parts stores. Use the fuse puller to remove fuses without damage. Don't use pliers! To check a fuse, simply look at the U-shaped connector. If the connector is melted through, the fuse is blown.
The W204 Fuse Boxes and Fuse Testing
There are three fuse boxes; located in the engine compartment, trunk and cabin as shown above. Use the Fuse Diagram found with the fuses, or attached below, to determine fuse location and amperage. Note: US spec models may have no fuses in the left-side instrument panel.
Find a bad fuse by checking continuity with a multi-meter. Ensure the ignition is OFF. Test each fuse by placing the leads in the fuse test ports as shown. If the fuse is good, the continuity tone will sound and resistance will be zero. A blown fuse will show infinite resistance with no tone.
The W204 Fuse Allocation Chart
Use the Mercedes fuse allocation chart to locate a specific fuse and amperage. For instance, the reading lamps are on fuse #17, rated at 30 amps and located in the under hood box.
How Many Times Can I Replace the Same Fuse If It Keeps Blowing?
Replace the fuse once. If it blows again, there is a fault on that circuit that must be tracked down.
A 15 Amp Fuse is Blown and the Only Spare I Have is a 30 Amp. Can I Put a Higher Amp Fuse in Place of the Rated Fuse?
NO! The fuse is rated to blow before overheating causes problems. The higher rated fuse will continue to carry current on overheated wiring, which could severely damage components or start a fire.
I Can't Seem to Find My Fuse Guide. Where Might it Be?
Try looking in the tool bag, in the spare tire well.
Inoperative Turn Signals, Headlamps, Engine Starter Problems, etc., Have Been Reported
These are typically software issues and not related to any fuse problems.
The Cabin Fuse Box in the Instrument Panel Appears to Have No Fuses
US spec models may not have fuses in that fuse box, because the equipment served is not available here.
Technical Service Bulletins (TSB)
There are no TSBs specifically related to fuse issues for the W204 C-Class.