2022 Peterbilt 579 — Fuse Box Diagram & Amperage

Quick answer

• Under‑hood power distribution module (PDM): Passenger side of engine bay (firewall/inner fender area, behind a cover). Houses maxi‑fuses, MIDI fuses, and key relays for engine management, aftertreatment, cooling fan, and lighting feeds.
• Cab/dash fuse panel: Driver’s left kick‑panel/under the steering column behind a removable trim door. Contains most mini fuses for interior circuits (blower motor, A/C clutch, radio/infotainment, 12V power/cigar, lighting, ABS control, ignition/run, etc.) and several micro relays.
• Sleeper/cargo (if equipped): Sleeper bunk/sleeper control panel area (right rear cabinet or behind a small service panel near bunk HVAC controls). Feeds sleeper 12V outlets, dome/reading lights, bunk blower, refrigerator/inverter control (when fitted).

Note: Exact cavity numbers and fuse values vary with VIN, engine (PACCAR/Cummins), day cab vs. sleeper, and option content. Always verify against the printed legend inside the fuse box cover and the chassis wiring label.

Under‑hood Power Distribution Module (PDM)

The under‑hood PDM carries the high‑current feeds and several engine/aftertreatment circuits. Typical contents are below; confirm the cavity numbers and ratings on your lid legend.

Common relays in this box (locations vary by build):

• Fan clutch relay
• A/C clutch relay (sometimes in cab panel depending on VIN)
• Headlamp relay(s) or headlamp power feed relay
• Aftertreatment/DEF pump relay
• Starter control relay (on some configurations)

Cab/Dash Fuse Panel (driver kick‑panel)

This is the main interior panel for most customer‑serviceable fuses.

Relays often found in/near this panel:

• Blower motor relay
• A/C clutch relay (if not under‑hood)
• Headlamp high/low relays (on some builds)
• Trailer brake relay / trailer charge relay
• Ignition/run relay

Sleeper/Cargo Fuse Panel (if equipped)

Sleeper‑equipped 579s typically include a small service panel near the bunk controls or in the right rear cabinet.

Relays in this area (varies):

• Sleeper blower relay
• Inverter enable relay (if equipped)

Important: Peterbilt uses multiple harness options. Your truck may combine some of the above in the cab panel and omit the sleeper panel on day‑cab models.

How to test a fuse

• Visual check: Remove the suspected fuse and look through the translucent body for a broken element. This is quick but not definitive.
• Test light method (preferred in‑vehicle): With key and circuit on, probe the two small test tabs on the top of the fuse. Both sides should light the test light. If only one side lights, the fuse is blown.
• Multimeter continuity: With the fuse removed, a good fuse will show near‑zero ohms. Infinite/open indicates a blown fuse.
• Verify power and load: If a replacement fuse blows immediately, stop. Check the circuit for shorts to ground, pinched wiring (hood hinge/headlamp harness, trailer pigtail, frame rail clips), or a failed component drawing excessive current.

Common blown fuses on this vehicle (what to check first)

• 12V/cigar outlet (20A): Often caused by phone chargers, dash cams, or inverters. Inspect the outlet for debris/loose sleeve and try a known‑good accessory. Check wiring behind the outlet for heat damage.
• Headlamp left/right (15A each typical): Repeated failures usually trace to chafed hood‑to‑cab headlamp harness or moisture in lamp connectors. Inspect the harness at the hood hinge and along the radiator support.
• Blower motor (25–30A): If it blows on high speed, suspect a failing blower motor or seized debris in the squirrel cage. Measure current draw; replace motor if excessive. Check the blower relay for heat damage.
• Trailer brake/trailer charge (20–30A): Shorted 7‑way connector, damaged trailer umbilical, or corroded junction box at the rear cross‑member. Inspect and test with a different trailer.
• ABS/trailer ABS power (30–40A): Look for rubbed/chafed wires along the frame rails and near suspension components. Water intrusion in wheel‑speed sensor connectors can also cause intermittent issues (though not typically a blown fuse).
• Radio/infotainment (15A): Aftermarket add‑ons tied into the radio feed can overload the circuit. Remove add‑ons or move them to a dedicated fused feed from the body‑builder or spare circuits.
• ECM/ignition (10–20A): Rare to blow without a wiring fault. If it does, inspect engine harness runs near the EGR/DPF components and at the back of the engine for heat and abrasion.

Tip: Fuse cavity numbers and amp ratings vary by VIN and options. Always confirm the exact fuse number, location, and rating from the legend molded or printed on the fuse box lid/cover before replacing.

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