Car Door Lock Fuse Keeps Blowing – Detailed Troubleshooting!

Imagine being ready to leave for work or an important meeting, and you find that your car door lock fuse has blown again. Luckily, diagnosing and solving this issue is easy.

Your car’s door lock fuse keeps blowing primarily because of a faulty actuator. Other common problems include internal short-circuit, faulty door lock switch, incorrect amp rating, faulty relay, or damaged wirings. Diagnosing all components related to the locking system is required to pinpoint the problem.

Now, let’s talk about the causes of why the car door lock fuse keeps blowing.

Why Does Car Door Lock Fuse Keep Blowing? Quick Troubleshooting

Car fuses can end up getting blown for various reasons. The most common reason for a door lock fuse to keep blowing has a faulty actuator. The other reasons include an internal short circuit within the actuator, using an incorrect fuse, a faulty door lock switch, and damaged or frayed wirings. 

To troubleshoot and identify the source of the issue, first, ensure that the fuse has the correct amp rating. If the fuse is fine, then the door lock switch may be faulty. You should check and verify whether it’s the driver’s side switch or the passenger’s side switch that’s causing the fuse to blow. 

After testing all switches, check what happens when you use the key fob. If it blows, then it might be one of the actuators causing the issue. Then, you need to diagnose each door individually to determine which door is causing the problem and which action(lock/unlock) is causing the fuse to blow.

Does it blow while locking the doors, or it blows while you try to unlock them? Both cases indicate the actuator is faulty or has an internal short circuit. Now, to find which actuator is the problem, remove all the actuators from all the doors and connect them one by one to see which one causes the fuse to blow.

If everything seems fine, then move to the relays for physical damage, short circuit or damaged/burnt/frayed wirings. If you find that the wiring is loose or damaged, consider replacing them with good-quality wires recommended by your vehicle’s manufacturer.

That was a short troubleshooting walkthrough. Now let’s discuss all the reasons, and how to diagnose them thoroughly, along with easy-to-follow solutions:

Reason 1: Incorrect Amp Rating

One of the most important aspects is using the correct fuse that matches the manufacturer’s requirements. Never use a fuse with a high or low amp than the ideal ampere rating needed by the system. You can find the correct fuse number, size, and amp details on the fuse diagram on either the fuse box cover or in the user manual.

Reason 2: Faulty Door Lock Switch

Another common reason is the faulty actuator switch. If the switch malfunctions, it can draw excess power from the central locking system. As a result, the fuse can get blown, and the problem will remain unless you fix or replace the switch.

Diagnosis 1: Here are the steps to diagnose and confirm the issue.

1. Test if the fuse blows when using the fob to unlock the doors.
2. If the fuse does not blow when using the fob, determine if the fuse only blows when attempting to power lock the car and works fine when power unlocking.
3. If the fuse only blows when attempting to power lock, the lock wire for one of the doors (excluding the trunk) may be grounded.
4. Check the location where the wires go into the door for a potential grounding issue.
5. If the above steps do not resolve the issue, verify the conditions under which the fuse blows.
6. Check the interior lock switch, interior unlocks switch, fob lock button, fob unlock button, exterior door lock button, and exterior door unlock pad to determine the cause of the fuse blowing.

Solution: Replace the door lock switch. The procedure for replacing the door lock switch varies depending on your vehicle model and brand. Here’s a general guide on how to replace your car’s door lock switch.

Reason 3: ECU Malfunction

If the ECU is faulty, it will send incorrect signals to the door lock actuators causing them to draw more currents, eventually blowing the fuse. It can be either the actuator motor or the ECU itself, so a diagnosis is needed to determine which is the culprit.

Diagnosis: Faulty door lock switch malfunction is pretty common in Toyota vehicles. The following diagnostic procedure can be used if you own a Toyota.

[CAUTION! This diagnosis needs expert knowledge. Don’t attempt this if you don’t know what you’re doing]

Tools Required

1. One 12V Battery
2. One Ammeter

Step 1: Determine the source of the problem: The body ECU that provides power to the lock motors or one of the four door lock motors.

Step 2: Obtain the electrical wiring diagram and pin out information for the body ECU from techinfo.toyota.com.

Step 3: Identify the body ECU wiring harness connectors that feed the four motors.

Step 4: Note the difference in power supply to the two right-hand side motors, which are fed by the same body ECU pins, and the left-hand motors, which are individually fed.

Step 5: Apply 12V to each motor one at a time, with a polarity set to lock the doors. Reverse polarity (Negative to positive and positive to negative) if the doors unlock.

Step 6: Observe the current draw of each motor, keeping in mind that the two right-hand motors, when combined, will draw 2x the current of the individual left-hand motors.

Solution: If a motor pulls more amp than the others, replace that door lock motor. If all motors behave similarly, replace the body ECU.

Reason 4: Faulty Actuator

The actuator is responsible for converting energy into motion. It converts the electrical signal to mechanical power to lock and unlock the car doors. The fuse can blow if the motor malfunctions for some reason and draws excess current.

Diagnosis: A bad/failing/stuck actuator shows several signs, and if you have this issue along with a blown fuse, be sure that the actuator is the culprit here. Here go some common symptoms:

1. Unusual noises are coming from the door locks. It is normal for the actuator to produce operational noises. But bad actuators generally make loud noises when they lock or unlock. Also, noises will get louder, leading the actuators to fail.
2. You’ll face difficulty while locking or unlocking your car doors. The lock/unlock process will feel sluggish, erratic, and less responsive.
3. The lock system won’t work properly; it won’t hold the shafts as expected. Also, the keyless functionality won’t respond when you try to lock or unlock the doors.

Solution: If you face these symptoms, the actuator is faulty and needs replacement. Consider watching this video on how to test the door lock actuator of your car.

Summary:

Bad or failing actuators will cause unusual noises when the door locks or unlocks. You’ll face difficulty while locking or unlocking your car doors. Also, sometimes the lock system won’t work properly, compromising your vehicle’s security.

Reason 5:  Faulty Relay

If a relay is not functioning correctly, it can create a short circuit in the circuit, causing an excessive amount of current to flow and blow the fuse.

Diagnosis 1: Steps to diagnose your car door lock relay issue causing a blown fuse:

1. Locate the door lock relays from the fusebox, usually located under the hood. (The fuse box location will vary depending on the vehicle).
2. Remove all the door relays, and check the diagram to identify the door relays. The diagram is usually located inside the fuse box (attached to the box door). If you can’t find the fuse diagram look into the user manual.
3. Now, check if the fuse stops blowing after removing the relays.
4. If the fuse no longer blows, insert the relays back into the auxiliary relay box one at a time.
5. Observe if the fuse blows after inserting each relay and keep track of which relay caused the fuse to blow.
6. Replace the relay that caused the fuse to blow with a new one.

Solution: The faulty relay would need to be replaced to resolve the issue. The cost of replacing the door lock relay can range from $121 to $195 and will vary based on the type and model of the vehicle. 

The cost will vary depending on your location, relay brand, vat/tax, etc. In luxury cars, service parts may cost more because they are more expensive.

Reason 6: Short Circuit

Another reason the fuse keeps blowing is a short circuit in the actuator circuit board or the wiring connecting the actuator. It can happen if the wiring is loose or the insulation of the wire is damaged, voltage overload in the circuit, or due to faulty components.

Diagnosis: Here’s how you can easily diagnose if there’s any short circuit.

Tools Needed

1. Multimeter

Step 1: Disconnect the battery from the car and activate your multimeter by selecting either the continuity or resistance mode, depending on your multimeter’s capabilities. When selecting the resistance scale, it is advisable to keep it as low as possible.

Step 2: Now to test the circuit board, connect the black probe of the multimeter to the ground or chassis of the electrical circuit, while the red probe should be placed on the component you want to test. Ensure that both probes are touching a metal part of the circuit, such as a wire, component lead, or circuit board foil.

Step 3: After completing the test, you can examine the reading displayed on your multimeter. Start with the resistance mode and check for a value of 1 or OL, indicating a short circuit in the electrical circuit. In the continuity mode, a reading of 0 or close to 0 signifies the presence of a short circuit.

Solution: If there’s a short circuit in the actuator’s circuit board, you might need to replace the actuator circuit board itself because it cannot be fixed. You can, however, replace the gears, or the electric motor, separately if they are the problem.

Reason 7: Damaged Wirings

The actuator is connected to the central locking module with the wirings. If the wires are frayed or damaged, it can disrupt the normal current flow leading to a blown fuse. So, you must thoroughly inspect the wires for any visible damage and replace them accordingly. Check the wires for leaks and fix them if necessary.

Diagnosis: Inspect the wirings visually for physical damage, such as burns and frayed insulation. Disconnect all circuit components to isolate the issue. If the fuse still blows, it indicates a wiring problem. 

Solutions: Change and damage wires with heavy-duty wires recommended by your vehicle’s manufacturer for maximum longevity and durability. You can find the standard wire recommendation in the user manual 

Car Door Fuse Keeps Blowing While Using Key Fob

Many users experience this issue where the car fuse blows when using the keyfob. There are two conditions for this; some people face this issue while locking the doors, while others face it when unlocking the door with the key fob.

Diagnose:  If that’s the case, you need to diagnose which door is causing the issue thoroughly. You have to move the door panels of your car to check the actuator of each door for short, ground, motor damage, and switch wiring. It’s a time-consuming and complicated process, so get help from a mechanic. 

Car Door Fuse Keeps Blowing While Locking/Unlocking Manually

Alternatively, if the car door lock fuse is blowing while locking or unlocking the doors manually, you need to identify which door is causing the issue. You can diagnose this by manually locking and unlocking each of the doors. Here’s how to diagnose the car door lock actuators: How to Diagnose a Door Lock Actuator. After the diagnosis, replace the faulty door actuator accordingly.

However, If all the actuators are working fine, the Central Locking Unit (CLS) may have malfunctioned. In the CLS system, electrical signals are sent to the actuator for actions, so a shorted wire, faulty power supply, or grounding issue can cause a fuse to blow.

How to Diagnose the Central Locking System (CLS)?

To diagnose the central locking system (CLS), a diagnostic device is typically used to inspect the components of your vehicle’s locking system thoroughly. It allows access to the memory fault, which may contain error information.

Additionally, the diagnostic device can be used to read sensors and control some functions, which can provide specific information about the CLS issue. The following steps are involved in the diagnostic process:

1. Connect the diagnostic device to the vehicle’s OBD-II port.
2. Turn on the ignition keeping the engine turned off.
3. Run the diagnostic software on the device.
4. Read and clear any diagnostic trouble codes (DTCs) related to the CLS.
5. Perform a functional test of the CLS from the diagnostic device.
6. Check the sensor inputs and outputs since they monitor the various inputs and outputs of the system and send them to the control unit system.
7. Finally, inspect and test the system. If the fuse doesn’t blow anymore, it means the problem is fixed.

Note:

Diagnosing and fixing the Center Locking Locking System requires expert supervision. Also, some cars require reprogramming after servicing due to security coding. So, get the help of a mechanic who can diagnose the issues for you.

You can check out a detailed DIY central locking system diagnosis tutorial.How To Diagnose a Central Locking System

Summary:

To diagnose the Central Locking System (CLS), connect the diagnostic to the vehicle’s OBD-II port, turn on the ignition, and run the diagnostic. Check and clear the DTC codes, if any, test the sensors, and finally, inspect the actuators.

FAQ

Conclusion

Thank you for your patience. That was all about your query on the car door lock fuse keeps blowing. Hopefully, you’ve got the answers and the procedures. Remember to refer to the user manual for the correct fuse and amp rating to prevent further blowout. 

That was all for today, wear your seatbelts and drive safely. Until next time, goodbye.