The electronic control module, also called the ECM or PCM, is the computer that manages the electrical operations of a vehicle. The ECM fuse protects the computer from damaging voltage spikes and other electrical risks.
If your ECM fuse has blown, there will be a few symptoms that you can look for to verify that this is the problem.
If you have a blown ECM fuse, you may notice the engine frequently stalling or misfiring. You will also notice that the fuel economy decreases drastically, and the Check Engine Light stays on.
Read on to learn more about the symptoms you may notice when you have blown a fuse in the electronic control module. We’ll also talk about why your electronic control module fuse may repeatedly be blowing.
The Symptoms of a Blown ECM Fuse
A blown ECM fuse might show several signs, which are common to almost every vehicle. Most of these symptoms will be fairly obvious.
Let’s look at what you can expect.
1. The Engine Won’t Run Properly
When the electronic control module fuse gets blown, the system will fail. This happens because the failed fuse cuts off all the power between the power source and the vehicle itself. Without a proper power source, the engine won’t run properly, if at all.
One of the first things you’ll notice is that the engine won’t turn over when the key is inserted. This probably doesn’t come as a surprise since the electronic control module brings power to the engine.
If the engine makes any noise, you’ll likely observe that it continuously misfires or cranks without actually starting. Occasionally, you may find that the engine will start, but the car will not run smoothly. Instead, it will stall out repeatedly.
The misfiring and stalling will be sporadic. You may experience it repeatedly in a single day and then go a few days without problems.
This can look a little different depending on whether you have an automatic or manual vehicle.
2. The Check Engine Light Stays On
If the vehicle is starting, at least part of the time, you’ll notice that the Check Engine Light will illuminate and stay on. This light lets you know that your engine has a problem that must be addressed before moving forward.
At first, you may notice that the light comes on and then shuts off again. It may come on sporadically, depending on how long the fuse has been blown. After about a week of the fuse being blown, the light will stay on consistently.
This is usually true, but if the problem has advanced too far, you may not see any lights. Let’s talk about this next.
3. The Dash Lights Won’t Stay On
When the problem has advanced, you’ll notice that you aren’t getting any power to the engine.
In addition, you’ll see the dash lights illuminated for a moment to let you know there is an issue, but they’ll rapidly shut off again.
At this point, the vehicle isn’t going to start at all. In most situations, this will be the case.
4. Bad Fuel Economy
If the fuse is only damaged but not completely blown, you’ll rapidly start to notice that the fuel economy is failing. This will only happen if some electricity is still going to the ECM.
What happens in this situation is that the failing ECM will miscalculate the amount of fuel that the vehicle needs to make the trip. The engine will almost always calculate more fuel than it needs.
The result of this is downright terrible fuel economy. Over time, you may also notice that the power is reduced.
If you have an electric vehicle, you may notice a similar situation with the vehicle holding less of a charge over time.
Poor fuel economy can be a symptom of many other issues or engine error codes as well, so it’s best to survey other symptoms to confirm that your ECM fuse has blown.
5. The Battery Drains Rapidly
Another symptom you may notice when the electronic control module fuse is blown is that the battery is constantly drained of power.
It may seem like you’ve only been in the car a few minutes, and the battery will be almost completely dead.
This happens because the ECM provides power to the battery. When the ECM fuse is blown, it can leave small amounts of power flowing through, which will run the vehicle.
However, this amount of power cannot sustain the car continuing to operate. As a result, you will notice that the battery has no power.
Why Your ECM Fuse Is Blowing Repeatedly
There’s nothing worse than examining whether the problem is a blown ECM fuse, fixing it, and then having it blow again after only a few days.
However, you will often notice that the ECM fuse is repeatedly blowing. This can happen for a few different reasons. Let’s talk about why this has become a recurring problem.
1. The O2 Sensor Isn’t Placed Correctly
Some people think a constantly blowing ECM fuse is due to a problem with the O2 sensor. However, the real issue is that the O2 sensor isn’t in the correct location.
Really quickly, let’s address what the O2 sensor does. This sensor is located within the emissions control system. When it’s functioning properly, this sensor sends information to the electronic control module about the vehicle’s performance.
It also ensures that your emissions are in check and not becoming too excessive. What does this have to do with a blown ECM fuse? Well, it’s a bit of a domino reaction.
If the sensor isn’t in the right place, the wires connected to the sensor may cause unwanted friction against the exhaust. The result of this friction eventually causes the O2 sensor to blow the ECM fuse.
Unfortunately, your ECM fuse will continue to blow until you put the sensor into the correct alignment so that the wires stop rubbing the exhaust.
2. The Fuel Pump Is Going Bad
This is one of the most common causes of an electronic control module fuse that blows repeatedly.
One of the problems with a fuel pump starting to go bad is that it gets too hot. The overheating fuel pump requires more electrical strength to function.
As the fuel pump requires more and more energy to function, it often uses more electrical power than the ECM fuse allows for.
When the capacity of electrical power the fuel pump requires exceeds that of the ECM fuse, it blows.
If the fuel pump is the culprit, the best way to fix this issue is to replace it.
3. Short-Circuiting in the Wiring
Another problem that can cause the electronic control module fuse to blow frequently is short-circuiting in the wiring. This happens more often than you would first expect. Let’s look at what happens during this process.
If a wire connected to the ECM becomes damaged in any way, it will likely start to short circuit. A short-circuiting wire causes dangerous voltage spikes, which cause the ECM’s fuse to blow.
A faulty wire is difficult for a layperson to find. There are quite a few, and this can be time-consuming. It’s best to leave this issue to a trusted mechanic.
4. The Starter Is Failing
The starter gets your vehicle up and running, which can use up a lot of power between the battery and the starter.
With a faulty starter, power ends up going to the ECM instead of to the starter. At this point, we know that when the ECM receives too much power, it causes the fuses to blow. A faulty starter is another way to send too much power to the ECM.
The voltage surges during this time, and this can result in the fuse blowing repeatedly. This will continue to happen until the starter is replaced. If your vehicle doesn’t start or it clicks when you try to start it, you might have a dead starter.
What You Can Do if the ECM Fuse Is Blown
You’d want to look at if the ECM fuse is blown. This is applicable primarily if you find that the fuse is repeatedly blowing.
One of the first things you’ll want to do is check for shorts within the wiring. As we discussed, it’s best to have a professional do the in-depth look, but you can do an overview glance before taking the vehicle to a professional.
Another thing you’ll need to do is check for a damaged starter. As we discussed, the starter can be a major reason your ECM fuse blows over and over.
The most common sign that the starter is failing is hearing a clicking noise. This will likely happen when you are attempting to start your vehicle. It may also occur while driving.
You’ll also want to check out the fuel pump. Some of the indicators of a damaged fuel pump include the following:
- Engine sputtering at high speeds
- A vehicle that is overheating
- A low fuel pressure gauge
- A lack of power
- Terrible gas mileage
Finally, be sure and check the position of the oxygen sensor. We discussed a misplaced oxygen sensor could rapidly blow the ECM fuse. Look for wires that are rubbing against the exhaust and creating a ground.
That’s all there is to it! Be sure to take care of these issues promptly. Not taking care of the problem ahead of time can lead to replacing the entire electronic control module, which can be very costly!