MB Medic Mercedes-Benz Repair Guides, Service, How To DIY
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In this guide (8 sections)
Trying to find the fuse box location on your Mercedes-Benz? Whether looking for the cigarette, lighter, radio, COMAND, or Navigation fuse location, you will find all of them here.
A W166 spreads its fuses across six panels including two prefuse boxes, so start from what has stopped working rather than from a fuse number.
- One interior item dead. Side of the dash on the passenger side, or the rear box by the rear seat for anything at the back.
- One engine or chassis item dead. Engine bay fuse box on the passenger side.
- Several unrelated systems dead at once. A prefuse, not a fuse. There are two: one in the engine bay by the bonnet hinge on the passenger side, and one under the passenger seat. A prefuse feeds a whole panel downstream, so a single blown prefuse takes out everything behind it and presents as catastrophic electrical failure.
- Car completely dead, or dead after sitting. There is a battery protection fuse box by the rear battery in the boot on the passenger side. On a W166 with the auxiliary battery setup that box is worth checking before you condemn a battery.
That prefuse rule is the one worth remembering. Four dead systems with nothing obvious in common is almost always one prefuse upstream rather than four faults.
Press Ctrl and F, or Command and F on a Mac, and type the fuse number or the circuit you are chasing rather than scrolling every chart.
Where the Fuse Boxes Are on a W166
- Engine Bay Fuse Box (Passenger Side)
- Engine Bay prefuse Box ( Engine bay, by the hood hinge, pass. side)
- Fuse box in the interior of the vehicle. Side of the dash on the pass. side.
- Prefuse box under the passenger seat.
- Rear fuse box by the rear seat.
- Fuse box for battery protection. By rear battery in the trunk, passenger side.
Which Fuses the W166 Uses
The ATO and MAXI fuses are installed on the fuse box panels. All these fuses can be purchased on Amazon; links are provided below. They are inexpensive when purchased online.
Models and Years Covered
| Model: | ML350 ML400 ML550 ML63 AMG ML250 Diesel |
| Years: | 2012 2013 2014 2015 2016 |
| Chassis: | W166, GLE |
| Make: | Mercedes-Benz |
Interior Fuse Box, Dashboard Passenger Side
The interior fuse box is located on the side of the dash. You will find the fuse box if you look at the passenger side of the dash. A plastic cover can easily be removed. Use a Dash Trim Removal Tool to avoid damaging the dashboard.
Fuse List for the Dashboard Box
| Fuse | Location, Purpose, Designation | Ampere |
| 10 | Ignition Lock | 7.5 |
| 11 | Steering column | 10 |
| 12 | Instrument cluster | 5 |
| 13 | Blower fan air conditioner | 15 |
| 14 | Connector | 5 |
| 15 | Upper control panel | 5 |
| 16-18 | not used | – |
| 19 | Air Conditioner | 15 |
| 20 | Steering column | 5 |
| 21 | Audio / Radio / COMAND /Stereo | 5 |
| 22 | not used | – |
Fuse and Relay Box Under the Rear Seat
To access this fuse box, you must fold the rear passenger seat forward. Under the seat, you will see a box with relays and fuses inside. To access the fuses, press the tabs on the front of the box and lift the panel cover. List of fuses under the rear seat. Here you will find fuses F100 to F157.
| Fuse | Function, Purpose, Designation | Ampere |
| 100 | Radio, COMAND, Navigation, Stereo DVD, Nav | 5 |
| 101 | Trailer Hitch | 20 |
| 102 | Driver Seat Controls | 7.5 |
| 103 | Passenger Seat Control | 7.5 |
| 104 | Telephone/Antenna Amplifier | 5 |
| 105 | Navigation | 5 |
| 106 | Liftgate | 5 |
| 107-109 | Not used | – |
| 110 | AdBlue for diesel engines | 5 |
| 111 | Trailer Hitch Connection | 15 |
| 112 | Fuel Electronics | 5 |
| 113 | Parking brake | 5 |
| 114 | Exterior lights | 5 |
| 115 | Trailer hitch | 5 |
| 116 | Districts Plus, Blind Spot Assist, Active Lane Keeping SENSORS | 5 |
| 117 | Night View Assist | 5 |
| 118 | Not used | – |
| 119 | Transfer Case | 5 |
| 120 | Fuel Sensor | 5 |
| 121-123 | Not Used | – |
| 124 | Brake Control Connector | 30 |
| 125 | Not used | – |
| 126 | Trailer Hitch | 15 |
| 127 | Driver seat Controls | 30 |
| 128 | Trailer Recognition | 20 |
| 129 | Passenger Seat Controls | 30 |
| 130 | Trailer Recognition | 20 |
| 131 | Not Used | – |
| 132 | Fuel System | 25 |
| 133 | Stationary Heater | 5 |
| 134 | Seat occupancy Sensor, child sensor, front passenger | 5 |
| 135 | The light bulb glove compartment | 5 |
| 136 | SRS, Airbag | 7.5 |
| 137 | Camera, Toll Conection | 15 |
| 138 | Anti-roll system, car stabilization | 15 |
| 139 | Not used | – |
| 140 | AdBlue System for Diesel Vehicles | 7.5 |
| 141 | AdBlue System for Diesel Vehicles | 15 |
| 142 | AdBlue System for Diesel Vehicles | 20 |
| 143 | Not used | – |
| 144 | Not used | – |
| 145 | Cup Holder / Temperature | 7.5 |
| 146 | Rear window heater | 30 |
| 147 | Radio / Comand / Audio / Navigation | 30 |
| 148 | Cigarette Lighter / Output | 15 |
| 149 | Not used | – |
| 150 | Outlet 12-volt back/trunk/cargo area | 20 |
| 151 | Outlet back seat, socket 12 volt | 20 |
| 152 | Control Unit N10/8 | 30 |
| 153 | 115 Volt Outlet fuse – AC Converter | 25 |
| 154 | Rear liftgate | 40 |
| F157 | Circuit 15R1 | 15 |
Relays Under the Rear Seat
| Relay | Purpose |
| A | Power Outlet |
| B | Rear window heater relay |
| C | Backup |
| E | Circuit 15 |
| F | Rear window wiper |
| G | Circuit 15R1 |
| H | Not used |
| I | Backup |
Engine Compartment Fuse Box
A fuse and relay box are located in the engine bay on the passenger side. To access this panel, open the hood and look on the left side of the engine. You will see the fuse box right behind the headlight. Remove the fuse cover by pressing on the locking tabs. Here you will find fuses F201 to F241.
| Fuse | Purpose, Function, Designation | Ampere |
| 201 | Not used | |
| 202 | Stationary Heater | 20 |
| 203 | Alarm, Antitheft System | 5 |
| 204 | ESP | 25 |
| 205 | Horn | 15 |
| 206-212 | Not used | – |
| 213 | Engine Electronics | 7.5 |
| 214 | Engine Electronics | 15 |
| 215 | Radiator Actuator, Connector | 15 |
| 216 | Engine Compartment Electrical, Engine Mount | 15 |
| 217 | Electrical Connector | 20 |
| 218 | Not Used | – |
| 219 | PAir cooler pump | 10 |
| 220-228 | Not used | – |
| 229 | Left headlight | 7.5 |
| 230 | ESP Electronic Stability Program | 5 |
| 231 | Right headlamp | 7.5 |
| 232 | Tranmission control unit | 15 |
| 233 | Bi-xenon headlight lamp, intelligent light | 15 |
| 234 | DISTRONIC, Active Blind | 5 |
| 235 | Wipers | 20 |
| 236 | Not used | – |
| 237 | Intelligent module, Direct Select | 30 |
| 238 | AIRMatic Air Suspension, Adaptive Damping System | 40 |
| 239 | Windshield wiper motor | 30 |
| 240 | Starter Motor | 30 |
Resources and Useful Links
Here is a list of useful resources related to the fuses and relays on the Mercedes-Benz M-Class W166 and GLE. These are external links.
- Fusebox and relay details
- Fuse charts that come with the carÂ
- Fuse diagram of the W166 /GLE, pictures
- Owner’s Manual for W166 M-Class.pdf
Which Fuse Do I Need to Replace a Blown One
Your Mercedes-Benz uses Automotive Blade Fuse Type. A box of 100 fuses that include all the different ampere ratings you need costs less than $20 on Amazon.
When replacing blown fuses, use the same ampere rating fuse. The fuse rating is written on the fuse. You can verify that you are using the correct fuse by ensuring the fuse colors match the blown fuse and the new fuse. This indicates the same ampere rating.- Make sure to close the fuse box cover properly and lock the tabs. This is very important to avoid any moisture getting inside the fuse box. The fuse box panel has a seal to keep water and moisture out of the box.
Fuses do not wear out. They blow because current exceeded the rating, so a blown fuse is a symptom rather than the fault.
- Blew once and the new one holds. An event. Note it and move on.
- The new one blows the instant you fit it. A dead short to ground, often where a harness crosses a bulkhead or runs near something that moves.
- Blows after a few minutes or only under load. A motor or component drawing too much as it heats up.
The fuse protects the wire, not the component, so a larger fuse only lets more current into a circuit that is already faulty. Keep a fuse assortment and a test light in the car instead.
When the Fuse Is Fine and the Circuit Is Still Dead
A W166 is late enough that almost nothing is switched by a relay you can swap. Circuits are controlled by module outputs, mostly the front and rear SAM, so the fuse can test good, the component can be good, and nothing happens because the module output has failed or because the module is not being told to switch it.
No scan tool can see a blown fuse. Nothing on the diagnostic socket can. What a scan tool does is read the module and report whether that channel shows an open circuit, an overload or a dead output, and on a car this networked it will also show you whether the request ever reached the module in the first place. That is the difference between replacing a part and replacing a module.
The YOUCANIC UCAN-II Pro reads every module on the W166 and GLE including both SAM units, so you can tell a dead output from a dead component. It covers nearly everything XENTRY does apart from online VIN coding.
A SAM with a burnt output is a board level repair rather than automatically a new module, which on a car this age also avoids the coding a replacement needs. Module Medics repairs front and rear SAM units.
Related Reading
M-Class W164 Fuse Chart
The generation before this one, also with two prefuse boxes.
Understanding the SAM Module
What a failed SAM output looks like when every fuse tests good.
S-Class W221 Fuse Chart
Six panels and prefuses, laid out the same way.
Where Is the OBD2 Port
Port location by model, for scanning the SAM.
Before you buy parts, scan every control module, not just the engine. It shows the root fault behind the warning lights and tells you whether the problem is still active. See how to do a full health check.
