The fuel pump runs continuously with your engine, delivering high-pressure fuel to the fuel rail and injectors.
The fuel pump keeps cool by staying submerged in fuel or else it would overheat.
If you make a habit of running your tank all the way to empty before filling up; your fuel pump will most likely die before its designed lifespan.
So, What if your engine was running fine with no hints of trouble; then you find it just will not restart:
- Maybe you stopped to fill the gas tank and the engine will not restart.
- You have been shopping and when you returned to the car, the engine will crank over but will not restart.
Is Your Fuel Pump Working ? Let’s Start With Some Basic Testing:
- Turn off the radio and close the windows to eliminate any noise in the car.
- Next, turn the key, so the gauges and warning lights come to life, but don’t start the engine.
- You should hear a buzzing sound when you turn on the key.
- This sound could be from under the car or in the back near the trunk.
The buzzing sound you are listening for sounds like an electric motor running. This sound is the electric fuel pump trying to prime the fuel system. It will only run for a few seconds and then shut off. If you are not sure you could hear it or if there is noise outside; you may have to try it several times.
Turn the key on and wait then turn it off. If there is no noise outside of the car you may need to try this; with the car door open so you can hear under the car. Keep doing this until you have confirmed if it works.
Many people recognize this sound every time they start the car but don’t realize it is the fuel pump running.
If you “DO NOT” hear the buzz of the fuel pump; then your engine has no fuel pressure, and we need to see why.
How To Determine If Your Fuel Pump Has Failed
The first thing you want to do is check the fuse panel to see if the fuse is blown. If your car has two fuse panels than the one in the engine compartment; should be the correct one to check. The fuse panel or circuit box is usually located near the battery; and is a small black box with a removable lid.
Inside the cover, you can find the fuse index if provided. Many manufacturers list the fuses by number and position inside the lid. If your car does not list the fuses in the lid; you will have to check your car’s owner manual for fuse and relay locations.
Pull out the fuse and hold it up to see if the element if broken. If so, you can replace it. Some fuse boxes supply extra fuses that you can use. Just make sure you use the same color fuse or one with the same AMP number listed on the top.
If the fuse is good then you will need to check the fuel pump relay next.
You can find the relay in the same circuit box. It will also be labeled on the box lid or in the owner’s manual.
Without proper test equipment you won’t be able to test the relay; but many of the relays in the box are the same AMP rating and size. If you switch the relay with a different one of the same size and rating; ( same amount of prongs on the bottom ); than you can try to start the car or listen for the fuel pump to run with the key on.
This will let you know if your fuel pump relay is bad. If this test works and the fuel pump runs; just remember to replace the bad relay before you drive the car.
Fuel Pump Circuit Breaker Reset
Some cars have a fuel pump circuit breaker instead of a fuse. If you cannot find a fuel pump fuse; then check your owner’s manual for the location of the fuel pump cut off breaker. Fuel pump breakers usually have a button on top that pops up when it trips. Simply push this button back in until it clicks. Check the owner’s manual for the exact location.
Fuel Pump Testing – If the fuse is good and the circuit breaker is not tripped; then the engine is not getting fuel pressure.
At this point many mechanics will open the rubber boot at the throttle body and; spray a small amount of starter fluid into the manifold; reinstall the boot and try to start the engine. In most cases, the engine will start and run for a second or two, then shut down.
This verifies that if the engine were getting gas, it would start correctly. This also verifies that the engine has no fuel pressure.
Electric fuel pumps on electronically controlled fuel injection systems need to; produce enough “high” pressure to allow the injectors to produce a sufficient spray of atomized fuel; into the intake path (or into the combustion chamber in a direct-injection system). Fuel pressure is typically in the 35 to 45 psi range.
Anti-Theft System Issue
If your Anti-Theft light is flashing; the anti-theft system is disabling the fuel pump to prevent the engine from starting.
The problem could be:
- A defective chip in a smart key
- Dead battery in a smart key or keyless entry fob
- A fault in the Anti-Theft system itself
Fuel Pump – Testing Checklist
- Bad fuel pump (Pump should run for a few seconds when ignition key is turned to start; no buzz means no fuel delivery to the engine).
- Blown fuel pump relay (Relay is energized by (PCM) to route power to fuel pump when ignition is on).
- Bad inertia fuel shut-off safety switch (Shuts off fuel in an accident, may have been tripped by a severe jolt, press button to reset).
- Open in wiring anywhere in fuel pump wiring circuit (power or ground). Problem may be at wiring connector on top of fuel tank (hard to reach!).
- No gas in fuel tank (Check the fuel gauge, and keep in mind the gauge may not be reading accurately).
- Bad gas (Contaminated with water or too much alcohol or diesel fuel). If you just filled up with gas and now your car won’t start, suspect bad gas.
- Plugged Fuel Filter (When was the filter last changed?). Replace the filter.
- Plugged or Pinched Fuel Line (Inspect fuel lines under vehicle for damage).
- Leaky Fuel Pressure Regulator (Controls fuel pressure to injectors, which is critical for starting and proper air/fuel mixture).
- No power to Fuel Injectors (Due to faulty fuel injector relay, blown fuse, no input signal to (PCM) from crank position sensor or cam position sensor, or bad (PCM) driver circuit). Injectors should usually have power when key is on. (PCM) grounds other side of injector circuit to pulse the injectors.
- Major vacuum leak (An open (EGR) valve, disconnected vacuum hose, (PCV) valve; can create a large vacuum leak and allow too much air to be sucked into the engine. This will make the air/fuel mixture too lean and make the engine hard to start. Engine will usually idle rough if it does start.
Proper Care Will Prevent A Fuel Pump From Failing Prematurely
Electric fuel pumps run continuously with your engine; delivering high-pressure fuel to the fuel rail and injectors. Fuel pumps keep cool by staying submerged in fuel. If you make a habit of running your tank all the way to empty before filling up; your fuel pump will most likely die before its designed lifespan.
This is due to the fact that when you shut off the engine with a low fuel level; the fuel can drain from the priming chamber designed into the fuel delivery system.
So when you restart your car; the pump runs hot and un-primed until it can refill the fuel chamber. Over time this will burn out the pump motor. This is why many pumps fail right after shutting off the car and restarting it while it is hot. Like when you stop to refill the tank with gas.
To prolong the life of your fuel pump, don’t let your fuel level drop below an eighth of a tank. This will prevent the pump from losing its prime and keep the pump motor cool.
Thank You !