2021 Freightliner Cascadia Fuse Box Diagram & Amperage
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Quick answer
On the 2021 Freightliner Cascadia, you will find two main fuse box locations:
- Under the Hood: Located on the driver's side of the engine compartment, near the firewall.
- In the Cabin: Located behind a kick panel on the passenger-side dashboard.
Under-Hood Fuse Box
| Fuse # | Amp | Color | Circuit / Component Protected |
|---|---|---|---|
| F1 | 30A | Green | ECM |
| F2 | 20A | Yellow | Fuel Pump |
| F3 | 15A | Blue | Ignition Coils |
| F4 | 20A | Yellow | Starter Motor Solenoid |
| F5 | 15A | Blue | Left Headlight (Low Beam) |
| F6 | 15A | Blue | Right Headlight (Low Beam) |
| F7 | 20A | Yellow | Left Headlight (High Beam) |
| F8 | 20A | Yellow | Right Headlight (High Beam) |
| F9 | 15A | Blue | Tail Lights & Park Lights |
| F10 | 15A | Blue | Brake Lights |
| F17 | 40A | Green | ABS Module |
| F18 | 30A | Green | Trailer Brake Control Module |
Relays in this box include:
- ECM/PCM Power Relay
- Fuel Pump Relay
- Ignition Relay
- Starter Relay
- Headlight Relays (Low and High Beam)
Passenger-Side Dash Fuse Box
| Fuse # | Amp | Color | Circuit / Component Protected |
|---|---|---|---|
| F21 | 30A | Green | Blower Motor |
| F22 | 15A | Blue | A/C Clutch |
| F29 | 20A | Yellow | Airbag Module |
| F30 | 20A | Yellow | Radio / Infotainment System |
| F31 | 20A | Yellow | 12V Cigar Lighter / Power Outlet |
| F33 | 10A | Red | Cabin Lights |
Note on Variations: The fuse numbers and amperage listed above are for the most common configuration of the 2021 Freightliner Cascadia. Trim levels and optional equipment can cause variations. Always verify the fuse locations and ratings by checking the diagram printed on the inside of your fuse box lid.
How to test a fuse
Testing a fuse is a simple process that can be done with a fuse tester or a multimeter.
- Safety First: Turn the ignition off and remove the key.
- Locate the Fuse: Use the diagram on the fuse box lid to find the fuse you need to test.
- Remove the Fuse: Use a fuse puller (often found in the fuse box) to gently remove the fuse.
- Visual Inspection: Look at the thin metal strip inside the plastic housing. If the strip is broken, the fuse is blown.
- Multimeter Test (for a more definitive test): Set your multimeter to the continuity setting. Touch one probe to each metal tab on the top of the fuse. If the multimeter beeps or shows a reading of 0 ohms, the fuse is good. If it remains silent or shows an open circuit (OL), the fuse is blown.
Common blown fuses on this vehicle
- Cigar Lighter / 12V Power Outlet (Fuse F31): This fuse often blows due to faulty phone chargers or other accessories plugged into the outlet. Before replacing the fuse, unplug any devices and inspect the outlet for any foreign objects.
- Headlights (Fuses F5, F6, F7, F8): If a headlight is out, the fuse is the first thing to check. If the fuse is blown, it could be due to a faulty bulb or a wiring issue. If the fuse blows again after being replaced, have the wiring inspected by a qualified technician.
- Trailer Brake (Fuse F18): This fuse can blow if there is a short in the trailer's wiring. First, check the trailer's wiring harness and connector for any damage.
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Before you pull a fuse on the 2021 Freightliner Cascadia
- 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 2021 Freightliner Cascadia
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
2021 Freightliner Cascadia 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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Values can vary by engine, trim and build date; check your VIN-specific service information. Updated 2026-07-16.