First off, fuel pump relays, are used to, supply power to the fuel pump, to start your car.
Because, they need a lot of power to run, using a relay, seemed like the logical choice.
Relays are basically all the same, in that they; enable a low amperage circuit, to switch on or off a higher amperage circuit.
So, now that we know, where fuel pump relays get their power from, we need to know what controls it.
There are actually, a couple of different things that control, the on/off power to the relay. Firstly, when you try and start the engine, the ignition switch, sends power to the relay. Next, the relay sends power, to the fuel pump to start your engine. Now, the power control module (PCM) takes over, and waits for the engine to start.
After the engine starts, the power control module (PCM) waits for engine oil pressure to build up. If everything goes as planed; the (PCM) then lets the oil pressure switch, have control over the power to the fuel pump. So, basically, fuel pump relays, act as a on/off switch for the fuel pump. They just have more than one thing that turns them on or off.
Failure Warning Signs Include:
Engine does not start
A common symptom of a faulty fuel pump relay is an engine that just refuses to start.
One of the most common symptoms of failing fuel pump relays is an engine that suddenly stalls. While the vehicle is running; the fuel pump relay suddenly cuts off power to the fuel pump, causing the engine to stall.
Loss of Power
The fuel relay may be the culprit, if the car suddenly seems to lose power while driving; or slowing down for no apparent reason.
Another symptom that may point to bad fuel pump relays is no noise from the fuel pump. The fuel pump can usually be heard when the engine starts. If the fuel pump relay fails; the fuel pump will receive no power and will not operate, thus it will be silent.
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