2018 Volvo VNR Fuse Box Diagram & Amperage
Locate and troubleshoot ECM, lighting, and accessory fuses on your heavy-duty Volvo truck.
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As an ASE-certified master technician, I know firsthand that tracking down an electrical gremlin in a heavy-duty commercial truck like the 2018 Volvo VNR can be a daunting task. Whether you are losing power to your trailer lights, dealing with a dead radio, or trying to start a truck with no ignition power, knowing exactly where to look for your fuses is the first step. Below is the comprehensive fuse box diagram and amperage guide for the 2018 Volvo VNR.
Quick answer
The 2018 Volvo VNR typically features two primary fuse and relay locations. Because this is a Class 8 heavy-duty truck, the locations differ significantly from passenger vehicles:
- Main Dash Power Distribution Center (PDC): Located inside the cab, directly under the top dash cover panel in front of the passenger seat. You remove the screws or clips on the top cover to access the main fuse and relay board.
- Battery Box / Frame Power Distribution Center: Located outside the cab near the main battery bank on the frame rail. This houses the high-amperage mega fuses, starter relays, and main power feeds to the cab and engine control module.
Note: Heavy-duty truck electrical systems vary significantly based on factory options, engine choice (Volvo D11/D13), and upfitter additions. The tables below represent the most common configuration. Always verify against the printed legend located on the inside of your fuse box lid.
Main Dash Power Distribution Center (PDC)
This is the central nervous system for your cab's interior electronics, exterior lighting, and various control modules. Relays for the blower motor, ignition, and wipers are also mounted to this board.
| Fuse # | Amp | Color | Circuit / Component Protected |
|---|---|---|---|
| F1 | 15A | Blue | Engine Control Module (ECM) / Vehicle ECU Ignition |
| F4 | 20A | Yellow | Headlights (Low/High Beam Control Module) |
| F6 | 15A | Blue | ABS / Traction Control System (Ignition Feed) |
| F9 | 10A | Red | Instrument Cluster / Driver Information Display |
| F11 | 20A | Yellow | 12V Power Outlet / Cigar Lighter |
| F12 | 15A | Blue | Radio / Infotainment System / CB Power |
| F14 | 30A | Green | Blower Motor / HVAC Controls |
| F17 | 10A | Red | Airbag / SRS System |
| F21 | 20A | Yellow | Tail Lights / Park Lights / Clearance Lamps |
| F24 | 15A | Blue | Brake Lights / Stop Lamp Switch |
| F28 | 10A | Red | Power Mirrors / Heated Mirrors |
| F31 | 15A | Blue | A/C Compressor Clutch Relay |
| F35 | 30A | Green | Trailer Brake Controller Power |
| F37 | 20A | Yellow | Power Windows (Driver / Passenger) |
| F41 | 15A | Blue | Diagnostics / OBD / 9-Pin Connector Power |
Relays commonly found on this panel include the Ignition Relay, Accessory Power Relay, Headlamp Relay, and HVAC Blower Relay.
Battery Box / Frame Power Distribution Center
Located near the battery bank, this distribution center protects the main power circuits before they reach the cab or the engine mounted components.
| Fuse # | Amp | Color | Circuit / Component Protected |
|---|---|---|---|
| MF1 | 150A | Black | Main Cab Power Feed 1 |
| MF2 | 150A | Black | Main Cab Power Feed 2 |
| MF3 | 125A | Black | Alternator / Charging System Output |
| F1 | 30A | Green | Fuel Pump Control / Lift Pump |
| F2 | 20A | Yellow | Engine Control Module (ECM) Constant Battery Power |
| F3 | 30A | Green | Starter Relay Control / Solenoid Feed |
| F4 | 30A | Green | Trailer ABS / Trailer Auxiliary Power |
| F5 | 30A | Green | Transmission Control Module (I-Shift) Power |
Heavy-duty starter relays and main battery disconnect relays are also integrated near or within this box.
How to test a fuse
When you're out on the road, visually inspecting a fuse isn't always enough. Sometimes a fuse can have a hairline fracture that looks fine to the naked eye but fails to pass current. Here is how a master technician tests a fuse:
- Grab a Multimeter: Set your digital multimeter to the DC Voltage setting (usually 20V DC).
- Turn the Key On: Ensure the key is in the ON position (engine off) so that power is flowing to the circuits.
- Ground the Black Lead: Place the black probe on a solid, unpainted metal ground (a door hinge or exposed frame bolt works well).
- Probe the Fuse: Take the red probe and touch the small metal testing tabs on the top of the fuse.
- Check the Readings: Touch one side, then the other. If you see around 12-14 volts on both sides, the fuse is good. If you have voltage on one side but 0 volts on the other, the fuse is blown and must be replaced. If neither side has voltage, the circuit is not currently receiving power (the relay may be off, or a larger upstream fuse is blown).
Common blown fuses on this vehicle
Based on typical service bay visits, here are the most common electrical faults on the 2018 Volvo VNR:
- 12V Outlets / CB Power (Fuse F11/F12): Drivers frequently overload the 12V sockets with heavy-draw accessories like portable coolers, inverters, or high-power CB radios. If your accessories suddenly die, check F11 and F12 first. Make sure your devices aren't exceeding the 20A limit.
- Trailer Clearance / Marker Lights (Fuse F21): The connection between the tractor and the trailer takes a lot of abuse. A shorted pigtail or a damaged marker light on the trailer will instantly pop the tractor’s tail/park light fuse. If you blow this fuse, inspect your 7-way connector and trailer wiring before replacing it.
- HVAC Blower Motor (Fuse F14): Heavy-duty trucks run their blower motors constantly. Over time, the blower motor pulls more amperage as the bearings wear out, eventually popping the 30A fuse. If this fuse blows repeatedly, you likely need a new blower motor.
- Trailer Brake / Aux Power (Battery Box F4): Corrosion in the trailer receptacle can bridge the power and ground pins, popping the auxiliary power fuse. Always keep your connections packed with dielectric grease.
Whenever you replace a fuse, always use the exact amperage rating specified. Replacing a 15A fuse with a 30A fuse might stop the fuse from blowing, but it will melt the wiring harness instead—a repair that costs thousands of dollars and causes immense downtime.
If you are dealing with a persistent short circuit, a module failure, or complex J1939 data link issues, it might be time to call in a professional. Find a trusted shop on Repairius.
Before you pull a fuse on the 2018 Volvo VNR
- Use the label printed on the panel cover or the owner's manual for your exact build. Layouts change with options, model year and build date, so a chart for another truck can be wrong.
- Replace a blown fuse only with the same amp rating. A larger fuse can let wiring overheat.
- A fuse that blows again right away means a short or failing component downstream. Find the cause before replacing it again.
- A good fuse doesn't prove the circuit works — relays, grounds and connectors fail too.
- Many heavy trucks have more than one power distribution point (cab, under-hood or near the batteries), and some circuits use circuit breakers instead of fuses. Some systems have 24-volt starting circuits; confirm the voltage before testing.
- Disconnect the battery before working near high-current fuses or cables.
Learn more: How fuses, relays and truck electrical systems work · Find mobile truck repair
More specs for the 2018 Volvo VNR
Oil Capacity & Filter
Capacity, weight, filter PN, drain plug torque, change interval.
Fluid Type Specs
Engine oil, coolant, ATF, diff, brake, PS, DEF — with OEM spec numbers.
Coolant Capacity & Type
Total system capacity, OEM coolant spec, flush interval, bleed tips.
Transmission Fluid & Service
Trans model, fluid spec, capacity, filter PN, service interval.
Torque Specifications
Lug nuts, drain plug, caliper, axle nut, plug, key fasteners.
Brake Pad & Rotor Specs
Pad PNs, rotor size, min thickness, caliper torque.
Tire Size & Pressure
OEM size, cold psi, bolt pattern, wheel size, TPMS.
Battery Size & Group
Group size, CCA, AGM/flooded, dimensions, reset note.
A/C Refrigerant & Oil
R-134a or R-1234yf, charge oz, PAG oil spec.
Bulb Sizes (Headlight, Tail, Fog)
Headlight, fog, tail, turn, reverse, interior.
Factory Maintenance Schedule
Service intervals by mileage, severe-duty notes, known issues.
Towing Capacity & Payload
Max tow, payload, GVWR/GCWR, hitch class by trim.
Serpentine Belt Routing & Length
Belt routing, length, rib count, OEM + aftermarket PNs.
Wheel Alignment Specifications
Camber, caster, toe ranges (front & rear), adjustability notes.
Paint Color Codes
All factory colors with paint codes, sticker location, touch-up tips.
Wiper Blade Sizes
Driver/passenger/rear blade size, attachment, OEM + cross-refs.
Spark Plug Type & Gap
Plug PN, gap, torque, interval by engine.
Transmission & Axle Gear Ratios
Trans gear ratios, axle ratios, RPO codes, tow vs MPG impact.
Key Fob Programming
DIY programming steps, FCC ID, fob PN, battery, transponder.
Same spec — other model years
Maintenance & repair guides
2018 Volvo VNR Maintenance Schedule →
Available maintenance guidance; confirm the manufacturer schedule.
Repair planning references →
Plan the scope of work; detailed procedures need configuration-matched evidence.
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