The PCM fuse is critical to the functioning of the powertrain control module in modern cars. If this fuse blows out, the PCM won’t control your car’s onboard computers and electrical components.
So, what is a PCM fuse, and how can you tell your car has a blown fuse?
This guide details everything you need to know about the PCM fuse. We’ll also discuss the causes of a blown PCM fuse, its symptoms, and how you can fix it.
Answer: PCM Fuse Meaning
The PCM fuse in your car is an electrical safety device that protects the powertrain control module against short-circuiting and abnormally high current loads. It transmits the appropriate currents to ensure the PCM functions optimally.
This fuse disconnects the auto circuits to protect the PCM from damage in case of overcurrent or short-circuit.
But what happens when excessive current goes through the PCM? In this case, the fuse has insulation that melts (blows out) to cut the current flow. That means the PCM ceases to receive more current and stops working.
The PCM controls your car’s engine control module (ECM), the transmission control module (TCM), and many other components. It serves as your vehicle’s computerized brain. The following are the common functions of the PCM:
- Ensures the engine works efficiently
- Controls ignition timing
- Allows efficient fuel delivery
- Ensures the engine receives a proper air and fuel mixture
- Controls the throttle body
- Controls emissions
- Controls idle speed
Answer: PCM Fuse Blown Symptoms
When the PCM fails due to a blown fuse, the ECM, TCM, and various car components won’t work properly. Knowing the symptoms of a blown PCM fuse can make your work easier while addressing the problem. So, what are the symptoms of a blown PCM fuse?
Starting Problems
One of the most common symptoms of a blown PCM fuse is car starting problems. When the fuse blows out, the PCM loses power and fails to control the ignition process.
The fuse cuts our current flow to various PCM components. When this happens, the engine won’t receive the spark that fires it into action.
Engine Stalling
The air and fuel supply in the engine relies on a functional PCM. The PCM controls the electrical signals needed during the opening and closing of the throttle body. If the PCM fuse blows out, there’ll be no signals to control the opening and closing of the throttle body.
As a result, the engine doesn’t receive the correct air and fuel mixture. The air and fuel imbalance causes the engine to stall and might not start until you’ve fixed the problem.
Check Engine Light
If you’re driving and the PCM fuse blows out, the check engine light might pop on the dash. An OBD-II scanner will help you determine if the fuse is the culprit.
Reduced Engine Performance
Are you driving, and your car loses power and fails to accelerate as it should? If so, a blown PCM fuse might be to blame. The blown-out fuse fails to control fuel flow into the engine. The car will bog down and eventually stall.
Question: What Causes the PCM Fuse To Blow Out?
The PCM fuse can blow out due to several reasons. The primary cause of a blown fuse is an electrical short resulting from damaged wiring.
If the wire harness becomes loose, wires can rub against each other and wear out. These wires might contact each other and cause short-circuiting.
Water in the PCM can cause current to flow through unintended paths and cause electrical shorts. These shorts can cause the fuse to blow out and fail to transmit current.
Besides causing electrical shorts, water can damage the PCM, causing the ECM, TCM, and other car components to malfunction.
Answer: How To Fix a Blown PCM Fuse
Before fixing a blown fuse, it’s essential to address the cause of this problem. If you fix the fuse without solving the underlying problem, the fuse will blow again.
So, check whether the issue stems from damaged wiring. Follow the wiring harness to and from the PCM to see if any look damaged. If you find frayed wires, wrap them with electrical tape. You can also use tape to secure the wires in the harness.
If you find wires that appear damaged beyond repair, replace them. For example, you can trace the wire from the battery to the PCM. If you find it broken or damaged, replace it.
If this wire appears okay, disconnect it from the PCM and inspect its pin. Replace the pin if it has melted and shorted against something.
You can also examine the connection point to ensure there’s no water. If there’s water, wipe it with a cloth and use a hairdryer or a box fan to dry the remaining water.
After resolving the underlying problems, you can proceed to fix the fuse.
Note that you can’t repair a blown PCM fuse. The best way to fix the fuse is by replacing it. The following materials will help you diagnose and replace a blown fuse:
- A multimeter
- A flashlight
- Protective gloves and goggles
- Relay puller pliers
- Replacement fuse
Use these steps to diagnose and replace a blown fuse:
Step 1: Turn off the Engine
Start by turning the engine off and disconnecting the negative battery terminal. When replacing the fuse, you’ll want to prevent electrical shorts that might cause a fire. Remember to wear your safety gloves and goggles when tinkering with the battery terminals and cables.
Step 2: Locate the Fuse Box
Like most electrical fuses in your car, you’ll find the PCM fuse in the fuse box. The problem comes when locating this box in your vehicle. In most cases, manufacturers install this box in the following areas:
- Beneath the steering wheel
- In the engine compartment
- Under the car seats
- Under the passenger floorboard
- In the trunk
- Behind the kick panels
If you don’t know where to find the fuse box in your car, consult the owner’s manual.
Step 3: Open the Fuse Box
Once you locate the fuse box, open the cover as guided in the car’s owner’s manual. The process of opening this box varies depending on the car’s make and model. So, consult the manual to get specific instructions.
Step 4: Find the Blown PCM Fuse
You can find the blown fuse visually by paying attention to any that appears black, cloudy, or melted. A blown fuse might also have a broken metal filament. Your flashlight should help illuminate the panel when finding the fuse.
If you can’t find a blown fuse, use the manual to locate the PCM fuse in the panel. Each fuse in the panel is labeled to help in identification. After locating the fuse, use your digital multimeter to measure resistance. If the multimeter reads “OL,” you have a blown PCM fuse.
Step 5: Remove the Blown Fuse and Install the New One
After finding the bad PCM fuse, pull it out with your relay puller pliers.
Ensure the new fuse is similar to the old fuse, with equal rating and amperage. A different fuse can be incompatible with your vehicle’s PCM.
Step 6: Test the New Fuse
Start the engine and check if the PCM works efficiently. The vehicle should not have starting problems, power loss issues, or the check engine light.
Final Thoughts
If your vehicle fails to start, bogs down while driving, or stalls, the possible culprit might be a blown PCM fuse. This fuse ensures your powertrain control module works properly to keep your vehicle up and running.
If the fuse blows out, the PCM won’t function, and the engine will stop working. If you’re considering fixing a blown fuse, locate it in the fuse box and replace it. Then test-drive your vehicle to see if you’ve successfully replaced the blown PCM fuse.