Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
System Relay
The function of the main relay (system relay) is to supply certain components with voltage.
The relay is mechanical and has a closing and opening function. In the rest position the circuit in the relay is open.
The main relay's terminals are supplied with voltage by the battery. When the Engine Control Module (ECM) is powered, one of the terminals on the main relay is grounded by the Engine Control Module (ECM).
When this terminal is grounded, the relay pulls and voltage is fed to a number of components via one of the relay's other terminals.
When the ignition is switched off, the Engine Control Module (ECM) performs internal checks. Once the checks are complete, which may take several minutes depending on the vehicle's equipment, market and external circumstances, the control module cuts activation of the system relay.
The main relay is in the integrated relay/fuse box in the engine compartment and is diagnosed by the Engine Control Module (ECM).
Use the Manual With the Right Hardware
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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