The fuel pump turns on and starts pressurizing fuel as soon as you turn the ignition on, even before you start the engine. That means the fuel pump is getting a signal from the ignition. So, if the fuel pump isn’t turning on, it doesn’t necessarily mean it’s faulty. As a matter of fact, there are several reasons why this that might happen.
If a fuel pump won’t turn on with ignition, it could be a faulty fuel pump relay, a bad ignition switch, or a triggered fuel cut-off switch, also called an inertia switch. And, of course, it could be a dead fuel pump.
What Causes Fuel Pump Won’t Turn On With Ignition
Replacing a bad fuel pump can get pretty expensive; however, there are three other things that could be causing this problem that are pretty cheap in most cases, if not free. So, here is what causes the fuel pump won’t turn on, explained in more detail.
Faulty Fuel Pump Relay
The fuel pump relay is integral to the entire fuel system. We can consider the relay as the primary switch for the fuel pump. When you turn the ignition on, it sends a low-voltage signal to the relay, which then closes the main fuel pump circuit and turns it on. So, if the fuel pump relay is faulty, which happens pretty often in older cars, the fuel pump can’t work.
Dead Fuel Pump
The fuel pump is a mechanical component for the most part which means it will fail inevitably. That said, there are usually some other symptoms that show up before the fuel pump dies outright. Those include a check engine light, poor performance, difficulty starting the car, random stalling, rough idle, and hesitation or jerking.
That said, it’s not uncommon for the fuel pump to work properly the entire time before it simply refuses to turn on one random morning. So, even if the fuel pump suddenly stopped working, it can still be the cause.
Faulty Ignition Switch
We already mentioned that the ignition switch sends a signal to the fuel pump to turn it on. So, with a faulty ignition switch, there is no signal going to the fuel pump, and it cannot work. So, if you were wondering can a bad ignition switch cause no power to the fuel pump, the answer is positive. However, ignition switch failure is extremely rare.
Moreover, the ignition switch also sends a signal to the ECU to turn on and to the starter motor. That means when the ignition switch is faulty, you also won’t be able to crank the engine. Plus, the dashboard warning lights may not light up, but that could also be a dead battery. And if the fuel pump is not getting power, in case you test it with a multimeter, the ignition switch should be your primary target.
Triggered Fuel Cut-Off Inertia Switch
All cars made roughly after the year 2000 have an inertia fuel cut-off switch. The purpose of the inertia switch is to cut the fuel supply to the engine in case of an accident. The switch is spring-loaded, and when the car crashes or experiences high and sudden G forces, regardless of the cause, the inertia switch pops up and shuts down the fuel pump.
Now the problem with this design is that hitting a bug pothole, a curb, or even doing some repairs near it can pop it up and shut the fuel pump down. Luckily, this is pretty easy to solve, as we will explain a little later.
What To Do If Fuel Pump Won’t Turn On With Ignition
If the fuel pump doesn’t turn on with ignition, you should first inspect all the components related to it, starting with the easiest ones. So, do the inspections in the order of the list below, in which we will explain how to test, fix, or how much it costs to fix each problem.
Triggered Fuel Cut-Off Inertia Switch – Fixes
To check the inertia switch, you first have to find it. Its location is different in virtually all cars and can be in the trunk, glove box, engine bay, and even under the seats. But you will find its location in your owner’s manual, so there is no need to go looking for it.
Once you find the inertia switch, you will see that it has a big red button on top. Now, if the switch is triggered, that button will be up, and all you need to do is push it down and disengage it. And if you are not sure if it’s popped up, it doesn’t hurt to push it down anyway, just to be sure.
Faulty Fuel Pump Relay – Inspection and Fixes
To check if the fuel pump relay is bad, first find where it’s located. In most cases, it’s in the engine bay fuse box, and you will find a complete diagram in your owner’s manual. Then, once you find it, remove the relay and its plastic cover. And if you notice any signs that its metal tabs are worn out, that it’s overheating, or that it’s corroded, replace it.
Alternatively, you can take it for inspection by any electrician. If it turns out the relay is faulty, you can get a new one for around $10 to $30, depending on the vehicle. And replacing it is just as easy as removing it; simply plug it back in.
Dead Fuel Pump – Inspection and Fixes
To test a fuel pump, you need a multimeter, and you need to find where it’s located together with how it’s wired. Once you have all that information, it’s pretty simple and takes no more than 5-10 minutes. Now, instead of me explaining how to do it, check out this ChrisFix video where he explains how to test the inertia switch, relay, and fuel pump.
If it turns out there is power to the fuel pump but not working, a new one for a standard car or a truck will set you back between $100 and $250, while labor will be $150 to $200. However, in some cars, the fuel tank needs to be removed when replacing the pump, in which case the labor cost can be as much as $800. Still, in the video above, you can see how to replace the fuel pump as well if you want to save some money.
Faulty Ignition Switch – Inspection and Fixes
Unfortunately, testing the ignition switch signal wires is not an easy task. You first have to remove the steering column trim to access the back of the ignition switch. Then, you need a multimeter and a wiring diagram for your specific vehicle. But since wiring diagrams and trim removal procedures are widely different for every car, it’s if you look for that information in a service manual or a model-specific forum.
On the other hand, you can have a technician do it for you, which will set you back around $50 to $100 and another $100 to $250 if you need a new one. Luckily, there is no need for key programming in most cases, which would add another $200 to the total cost.
FAQs
Why is my fuel pump not turning on when I turn the key?
There are a couple of possible reasons why your fuel pump is not turning on when you turn the key, including a bad fuel pump, bad fuel pump relay, bad ignition switch, or a triggered inertia switch. It could also be a blown fuse, but not all cars have a fuel pump fuse.
Why won’t the fuel pump come on?
If a fuel pump doesn’t come on, it could be faulty, or it could be a bad fuel pump relay, ignition switch, inertia switch, bad wiring, bad ECU, or a blown-out fuse. But most likely, it’s a bad fuel pump or relay.
Does the ignition switch control the fuel pump?
Yes, the ignition switch controls when the fuel pump turns on and off. When you turn the key, the ignition sends a low-voltage signal to the fuel pump relay, which then closes the main fuel pump circuit or power supply.
How do I know if my fuel pump is getting power?
To check if the fuel pump is getting power, you should first go under the car and have someone turn the ignition on. Then, if you hear buzzing, the fuel pump is working. And if not, you will need a multimeter and a wiring diagram for your car to test the fuel pump positive wire against the ground.
Does the ECU control the fuel pump?
No, the ECU doesn’t directly control the fuel in most gasoline cars. Instead, the ignition switch turns the fuel pump on and off. However, in modern direct injection engines, direct injection diesel engines, and returnless fuel systems, the ECU does control the fuel pump. More specifically, it controls not only when the fuel pump turns on but also the fuel flow.
What controls the power to the fuel pump?
The power to the fuel pump in most gasoline cars is constant, and the ignition switch turns the fuel pump on and off. There is also a fuel pump relay in those systems which is the main switch. However, in direct injection gasoline and diesel engines and those with returnless fuel systems, the ECU controls the fuel pump.
How do you restart a fuel pump?
To restart a fuel pump after a crash or after the inertia switch is triggered, turn the ignition on and off repeatedly a couple of times. And if that doesn’t work, you will have to check in your owner’s manual where the inertia switch is located and reset it manually, which is nothing more than pushing a button once you find it.
Final Words
So, now we know that when a fuel pump won’t turn on with ignition, you should first check the inertia switch, also called a fuel cut-off switch. And if that doesn’t work, check the fuel pump relay using our guide, and after that, test the fuel pump with the help of the video found earlier in this article. And if all else fails, you will have to figure out a way to test the ignition switch or take the car to a professional.
