How to clear OBD2 codes without a scanner

How to clear OBD2 codes without a scanner

Every motorist becomes annoyed when they see the malfunction indicator light come on. The good news is that the check engine light can be cleared even without a scanner.

The malfunction indicator light indicates many things. For example, this light could mean that your car has several problems, such as airbags, anti-lock brakes, or automatic transmission. But for those with older cars, your vehicle may come with a simple problem like a leaking gas cap or a serious one like a transmission issue.  

Find the problem first.

Before we proceed to the steps that you have to follow to clear OBD2 codes, it’s crucial to know the problem with your vehicle’s system. You need to reset the check engine light as the light comes on for a reason. It’s an indication of either a minor or severe problem.

If you clear the OBD2 code without identifying and fixing the main cause, you will be doing nothing as the light is still come on. Your car may be having an issue with the transmission system, or the gas cap may be loose and needs tightening. That’s why having a reliable OBD2 scan tool is vital and can help you detect and diagnose the problem before clearing the error codes.  

How to clear or reset the OBD2 codes without a scan tool

Step 1: Park your vehicle in a level and safe area. Ensure you’ve engaged the parking brake and open the hood.

Step 2: Next, remove the negative (-) black cable from the battery. If the cable is latched on tightly, use a wrench to loosen the clamps on the battery terminals.  

Step 3: Remove the positive (+) red cable that starts disconnecting the battery. It would be crucial if you never allowed the negative and positive cables to touch one another.

Step 4: When you’re done removing the cables, you will have to cycle the ignition switch/button to the “ON” and “OFF” positions between 3 and 5 times.

Step 5:  Afterwards, you will have to drain any power that’s left in the ECU. To attain this, you will be required to press the horn button on the steering wheel. You may have to press the horn for at least 30 seconds to drain out all the stored power in the ECU capacitor.

Related article: Check the Review of Heavy Duty Autel MS908CV ECU Programming Maxisys Scanner

Note that the horn is normally connected to a hot capacitor. That’s why the horn can be engaged regardless of the key position in the ignition. In short, you’re draining out all the electrical power in the ECU by simply pressing on the horn while the battery is disconnected.

Step 6: Even though this step is optional, it’s crucial to wait for at least 10 minutes before reconnecting the battery.

Step 7: You can now reconnect the battery cable to the car. Begin by connecting the positive red cable, followed by the black negative cable. Ensure to tighten the clamps on the battery terminals so that they do not disconnect easily.

Step 8: Switch on the ignition key and observe if there are any warning lights on the console. Then, start the engine and give it some time to warm up. At this juncture, the check engine light should be off.

If you couldn’t reset the check engine light without a scanner even after warming up the vehicle, there’s a chance that you didn’t drain the ECU fully. Therefore, you should repeat the procedure, ensuring to hold down the horn until all the power in the ECU is drained completely.

Even after following this procedure, it’s crucial to know that the check engine light or trouble codes cleared won’t go away for good if the issue is not handled. You may see the check engine light comes after a few days.

What are the problems that I may experience after clearing or resetting OBDII codes?

Clearing or resetting OBD2 codes without using a scanner is pretty simple. However, you may notice some challenges after you restart your car if you don’t have an advanced onboard diagnostic scanner like Fixd or Autel TS601 TMPS device.

Some problems emerge after clearing OBDII codes without a scan tool because you have to drain all the power from the ECU to reset the codes. When power is restored, your vehicle’s electronic settings will need to reboot. Besides, this means that your radio, clock, and drive settings are reset as well.

Typically, the problems that emerge after resetting the codes aren’t severe. Therefore, your car has to be reset to all of its settings after the ECU is drained. Note that this can take at least one drive cycle; thus, you shouldn’t worry if your vehicle isn’t behaving normally as soon as you turn it on.

Related article: Step-By-Step Guide on How to Read OBD1 Codes

One of the most common problems that you will face is with the transmission system. Since your vehicle is rebooting all of its electronics, the shifting in its automatic transmission won’t reset as needed instantly. Hence, you may have to drive some distance for it to go back to its normal condition.

Some types of cars feature built-in modes that keep your settings even if the ECU is totally drained of its power. Most such vehicles use a memory gadget that stores these settings separately. Therefore, you always have a backup, and the settings will load up automatically after the procedure.

What do I have to do if OBD2 codes return?

After clearing the OBD2 codes without using a scanner, you notice that the check engine light is back on. This is an indication that your vehicle’s system has a gravid issue. Take the car to the mechanic or acquire a professional diagnostic scanner to know what the problem is.

Never ignore a check engine light that keeps coming on. On top of that, you should get a quality scanner that can check multiple issues apart from drivetrain problems. If you can’t afford the high-end scanners, visit a professional mechanic as they usually have professional diagnostic scanners.


It’s not a must to clear OBD2 codes with a scanner. You can clear these intimidating codes with a simple wrench. However, removing the codes does not mean that you have tackled the problem that brought the MIL or CEL in the first place. So, you should use an OBD2 scanner to run a test and diagnose the problem. Without tackling the real issue, the check engine light will still come on.

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