Check the power distribution module under the hood near the battery and the secondary panel on the driver side dashboard to trace any electrical issue quickly.
The engine compartment unit uses high-current inserts rated from 30A to 80A, supporting systems like ignition, cooling fans, and control modules. The cabin section contains smaller blade-style components, typically 5A to 25A, assigned to lighting, infotainment, and accessory circuits. Each slot number is printed on the cover for direct reference.
If a component stops working, match the circuit to its position and inspect the internal metal strip. A visible break or burn mark confirms failure. Replace only with the same rating to avoid overheating wires or damaging connected devices.
Use a multimeter to verify voltage at both terminals of the slot. This confirms whether power is present and helps determine if the issue lies in the protective element, a relay, or the wiring path.
2015 GMC Sierra fuse diagram with panel layout and circuit assignments guide
Inspect the under-hood power distribution center first, as it handles high-load circuits such as starter control, cooling fans, and ignition feed.
This engine bay module combines cartridge-style and blade-type protection elements, grouped by system function. High-amperage slots typically range from 30A to 80A and support components like powertrain control, anti-lock braking, and trailer wiring circuits. Relays placed alongside these slots manage switching operations for devices that require stable current flow without routing power directly through cabin switches.
Inside the cabin, the secondary panel located beneath the dashboard controls lower-load electronics including audio system, interior lighting, and accessory outlets. Each position is labeled on the cover, allowing quick matching of a circuit to its slot; checking continuity and voltage at these points helps isolate whether the issue lies in the protective element, relay, or wiring.
Engine bay fuse panel layout and relay functions for key systems
Open the hood and locate the power distribution unit near the battery on the driver side, then remove the plastic cover to access the circuit map printed inside. This reference shows exact slot numbering, allowing quick identification of high-current protection links and switching components tied to ignition, cooling, and fuel delivery.
Primary assignments inside this under-hood module include circuits responsible for engine management, radiator fan operation, and starter engagement. Typical slots are labeled with amperage ratings such as 30A for cooling fans and 15A for control modules, helping match the correct replacement when diagnosing electrical faults.
Relay positions sit alongside protective links and control switching for major systems. Common relay functions include:
- Fuel pump activation during ignition cycle
- Cooling fan engagement based on temperature sensor input
- Starter control relay linking ignition switch to starter motor
- Air conditioning compressor clutch operation
Inspect terminals for corrosion or heat damage, as discoloration or melted plastic indicates overload or poor contact. Replace any compromised component using identical amperage and form factor, ensuring stable operation of engine-related electronics and avoiding repeated failures.