How to Clear OBD2 Codes: Step by Step Guide For Every DIY Mechanic

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Ever get a check engine light and have no idea what it means? How about your co-worker or friend who always seems to be fixing their car? OBD2 codes are a part of everyday life for many people. Whether you're an auto hobbyist or just someone who doesn't want to pay for costly repairs, this guide helps you understand how to clear OBD2 codes independently.

In this blog post, we'll go over how to use OBD scanners, hack into cars to clear OBD codes without a scanner, and if it's safe to disable check engine lights forever.

To clear codes using a scanner, start by connecting your scanner to the car, turning on your vehicle, and letting the scanner show the code you want to erase. Clear the code, then restart your vehicle to complete it.

How to Clear OBD2 Codes With a Scanner

Car scanner showing I/M readiness after erasing trouble codes

Clearing OBD2 codes with a scanner is the best option as your car understands the scanner action better than a reset using the battery hack mentioned above.

1. Hook the OBD2 scanner into the car's OBD2 port

Connect the OBD2 scanner to the OBD2 port on your car

Once you have worked on the trouble code causing the maintenance light to illuminate, insert the OBD2 scanner into the car's diagnostic port. Make sure your vehicle is off.

If using a wireless scan tool, wait for the light to turn on the scanner to see that it's working. If using a cabled scanner, wait for the scanner name to appear on the screen.

2. Turn the scanner and the car on

Car showing ignition is on

Turn the OBD2 scanner on or launch the scanner app on your mobile phone, then turn on the ignition key.

3. Press the clear button on the scanner

OBD2 scan tool showing how to erase trouble codes

Find the trouble code on your scanner by locating the stored codes, then erase it using the clear button.

To check if the warning light is still on, turn on your car's ignition. Again, if the warning light still appears on your dash, have your vehicle checked with a professional mechanic or get an advanced scan first to know the real issue with your car.

How to Clear OBD2 Codes Without a Scanner

You can clear OBD2 codes without a scanner, but it's not always the ideal solution. Often the code comes back on because your car's system hasn't detected a reset. You can still clear OBD2 codes without a scanner following these steps:

1. Remove the cables from your car battery

Removing the cables from the car battery

Make sure you parked your car in a safe place, preferably your garage, and the brake engaged. Next, remove the cables from the battery terminals, starting with the negative (black) cable, then the positive (red) cable.

holding the cables together for 30 seconds

Hold the cables together for 30 seconds to clear the codes.

2. Turn the ignition on and off 3-5 times

Press on the horn for 30 seconds to 1 minute to drain the ECU capacitor, so when you reconnect the battery, your ECU won't pick up the trouble code again.

3. Wait for 10-20 minutes

Some mechanics are okay with 1-2 minutes, but we recommend a longer wait to reset your car's ECU.

4. Reconnect the battery cables

This time, start with the red cable, then the black cable. Tighten the clamps well.

5. Check the check engine lights

Car dashboard showing cleared DTCs

Turn your ignition on to check the warning lights. If it is still on, repeat the process for a second time.

If the warning light persists, have your car checked with a professional mechanic, primarily if you have already worked on the trouble code previously identified. However, if you haven't corrected the trouble code, it's clear that it needs immediate attention.

What Does a Check Engine Light Mean?

The check engine light appears on your dashboard when your car's ECU detects a problem. Different things like a faulty gas cap, dirty sensors, or an intake manifold leak can trigger a Check Engine Light (CEL). Some guides use the terms Malfunction Indicator Lamp (MIL) or simply warning light.

Things to Remember About OBD2 Codes

• Fix the problem first before clearing the codes

The Check Engine Light is there for a reason. It may be minor such as loose caps, or major such as a defective catalytic converter. Whatever the reason, address the issue first, especially if the check engine lights up for the second time and your pending code becomes active.

• When the check engine light comes on while driving

When the CEL or MIL lights up while you're driving, it may cause you to panic. But if it is the first time to appear, it may be just a pending code and may not occur again. If it does, though, stay calm and find the nearest safe place to park so you can check on your car.

If you don't find anything strange, like a rattling noise or a peculiar smell inside your car, it is perfectly safe to drive your vehicle.

Problems After Resetting OBD2 Codes

Resetting the OBD2 codes forces your car's ECU to drain. After restoring the power, the electronic control systems of the vehicle may need restarting. This could mean that your clock is on a reset mode, or your transmission may have issues.

Modern cars use a memory device that stores this setting separately, so the backup automatically loads the necessary information. The automatic transmission's shifting system will not always re-initialize smoothly, though.

What To Do if OBD2 Code Comes Back On

If the Check Engine Light comes back on again after you have reset the codes, it may be a signal for a more serious issue that needs attention.

Swapping out your gas cap may help, but make sure nothing is wrong with the car. Try turning off the lights in your vehicle for a minute, then turn it back on again.

Bad sensors or code errors on your car's diagnostic system can signal a major problem. Check on your sensors first by getting a deep scan from a trusted mechanic to know the underlying factors to fault codes instead of immediately jumping into an expensive repair.

What Does an Incomplete Status Mean

Immediately after erasing your codes, your system may not still be ready. Some OBD2 scanners may reflect an exclamation point or the text Incomplete on your scan tool. It usually means that the car's OBD2 system has not run the readiness routine or failed.

To start the reset, erase all trouble codes on your OBD2 scan tool. Next, fill your gas tank to 85% to start the diagnostic testing.

To complete the reset, drive your car around for 50-100 miles in what mechanics call the OBD cycle drive. Cheat on your car by shutting off your engine, let your engine cool down for a few hours before driving again. The OBD cycle drive will usually take a week or so to complete.

Clearing OBD2 Codes FAQ

Do OBD codes clear themselves?

The light can clear itself, for instance, if you leave the gas cap off when refueling. The computer will then register a fault and enter it into memory while also recording how to fix it by putting your gas cap back on! Thanks to a built-in self-check feature of your car, the light will turn off by itself.

However, these are already pending codes in your car's ECU if it happened for the first time. When it occurs again, it becomes an active code and will cause your light to turn on when detected again.

Sometimes, it may detect the same code causing a different fault, like signaling a gas cap is off when the real reason is an ill-fitting or cracked gas cap.

Does disconnecting the battery clear the codes?

Yes, it does. However, be warned that disconnecting your batteries to erase trouble codes from your car also erases other onboard components, thus needing an update.

How long do you leave the battery disconnected to reset the ECU?

Depending on the guide, you may need 1-2 minutes or 10-20 minutes before you can reset the ECU after disconnecting the battery. However, if you opt for a shorter time, make sure to drain the ECU capacitor's power to erase the memory by sounding the horn and turning the headlights on.

What do clearing fault codes do?

Erasing error codes is a way to keep your car running smoothly. If you erase the errors, they'll be gone for good, and there will no longer be any information available about them in case something goes wrong with your vehicle again later on. However, erasing the codes won't do anything to pass smog or emissions testing.

Erasing error codes does not ensure that everything is healthy under the hood, especially if you cheated on clearing your error codes.

How do I permanently turn off my check engine light?

Drivers turn off their check engine light for several reasons. The check engine light may be defective and give you the wrong impression about your car or pass emissions testing.

You can permanently turn off the check engine light by removing the check engine light fuse. You can find the fuse under the dash and inside a small yellow box. The fuse box reads ROOM/PLAFON.

To remove the fuse, plug in a code scanner to the OBD2 port of your car, turn the ignition switch on and off, then press "read" on the scanner to check the engine light code. Clear the OBD2 codes by erasing them, then turn off the key.

Disconnect the battery from the negative terminal for 10-20 minutes. This step should reset the check engine light. Some mechanics suggest 1-2 minutes but turn on the headlights and the horn to deplete the capacitor faster.

However, we do not recommend disabling the check engine light permanently for these reasons:

  • If you're a casual driver who has no idea how to check your car, disabling your check engine light may  cause severe injuries and accidents.
  • It will cost you money to have your car checked periodically.


In this blog post, we've gone over how to use OBD scanners for your car and some hacks that will help you clear codes without a scanner.

 We also discussed if it's safe to disable check engine lights forever and why your car registers an incomplete reset on your OBD2 scanner. Have questions about this blog post? Let us know!