Here's why:
* Normal Operation: A brief buzz is often normal. The pump primes the fuel lines, ensuring there's fuel ready for the engine. The duration is key; a *very* short prime is usual.
* Faulty Fuel Pump: A buzzing sound for a longer duration, especially if it's weak or sputtering, suggests the pump motor is struggling or failing. The relay may be functioning correctly, but the pump itself is the issue.
* Low Fuel: Sometimes the pump will work harder if the fuel level is low, potentially leading to a longer buzzing sound.
* Wiring Issues: A problem with the wiring harness to or from the pump (corrosion, loose connection) can also cause the pump to struggle and make excessive noise.
* Faulty Relay (less likely): A faulty relay *could* cause the pump to run continuously or not at all. A brief buzz is less indicative of a relay problem.
To diagnose the problem:
1. Check the fuel level: Make sure you have enough fuel.
2. Listen carefully to the buzz: Is it a short, healthy-sounding prime, or a long, weak, or sputtering sound?
3. Check the fuel pump relay: Visually inspect the relay for any damage. You can often swap it with a similar relay (if your vehicle has several) as a quick test (ensure you consult your vehicle's manual first). But this is generally less likely the cause of a brief buzz.
4. Have a professional diagnose it: A mechanic can test the pump directly, check the wiring and the relay more thoroughly. This is often the best course of action.
In short, while a faulty relay is possible, a longer or unusual buzzing sound points more towards a fuel pump or wiring problem. A short, normal-sounding buzz is usually nothing to worry about.
