How to clear check engine light code?

The quick answer: you can erase the stored diagnostic trouble codes and reset the check engine light using an OBD-II scanner after you’ve diagnosed and fixed the issue. If the underlying fault isn’t addressed, the light is likely to return. This article explains how to do it safely and what you should consider before clearing codes.

What the check engine light means

The check engine light (CEL) signals that the vehicle’s onboard diagnostics system has detected a fault somewhere in the engine, emissions, or related systems. Diagnostic trouble codes (DTCs) are stored in the vehicle’s computer (the ECU/PCM) to point technicians toward the probable cause. A single fault can trigger multiple codes, and some issues may set a warning without immediate symptoms.

Before you clear the codes: diagnose and plan

Clearing codes without addressing the root cause is not a repair. Reading the codes helps you understand the potential problem, determine whether it’s a temporary issue (such as a loose gas cap) or a genuine fault, and decide whether service is needed. It’s also useful to know the difference between stored codes, pending codes, and the MIL (malfunction indicator lamp) status.

Step-by-step: clearing the codes

Use a consumer OBD-II scanner to erase codes and reset the MIL. The steps below describe a typical process; exact buttons and terminology can vary by device and vehicle.

1. Choose a reliable OBD-II scanner that includes an erase/clear function and, ideally, live data readouts.


2. Locate the OBD-II port under the dashboard on the driver’s side and connect the scanner to it.


3. Turn the ignition to the ON position with the engine off (or follow the scanner’s instruction for power-on). Establish a connection with the scanner.


4. Use the scanner to read and record the current codes. Note any pending codes as well as stored codes.


5. Repair or replace the faulty components as indicated by the codes and your inspection (if you are not sure, consult a mechanic before proceeding).


6. In the scanner, select the option to clear or erase codes and reset the MIL. Confirm the action when prompted.


7. Turn the ignition off, then back on, and start the engine. Take a short test drive to verify that the light does not return immediately.


8. Drive normally to allow the vehicle’s readiness monitors to complete their tests. If the MIL reappears, re-check for codes or consider professional diagnosis.

After the list, a short note: the exact drive cycle and the number of miles required for readiness tests can vary by make and model. If you still see the light or the same codes reappear, the repair may be incomplete or the fault may be intermittent.

Common codes and what they typically mean

Codes are grouped by system and are most commonly seen as P-codes (powertrain), but components in the body and networks (B-, C-, U-codes) can also trigger the MIL. Here are some frequently encountered codes and their typical interpretations:

• P0300 – Random/Multiple Cylinder Misfire Detected: A misfire detected across several cylinders; causes include faulty spark plugs, ignition coils, fuel delivery issues, or vacuum leaks.


• P0301 to P0308 – Cylinder 1 through Cylinder 8 Misfire Detected: Individual cylinder misfires; causes mirror those for P0300 but are localized to a specific cylinder.


• P0420 – Catalyst System Efficiency Below Threshold (Bank 1): Possible catalytic converter issue, faulty oxygen sensors, or exhaust leaks.


• P0430 – Catalyst System Efficiency Below Threshold (Bank 2): Similar to P0420 but for the opposite bank in V-engine layouts.


• P0171 – System Too Lean (Bank 1): Air intake or vacuum leaks, mass air flow sensor issues, or fuel delivery problems.


• P0174 – System Too Lean (Bank 2): Lean condition on the other bank; same potential causes as P0171.


• P0101 – Mass Air Flow Sensor Performance/Range Problem: MAF sensor faults or wiring issues, or dirty/intake air leaks.


• P0128 – Coolant Thermostat Regulation Temperature Not Reached: Engine not reaching proper operating temperature; may involve thermostat or temperature sensor.


• P0455 – Evaporative Emission Control System Leak Detected (gross leak): Large leak in the EVAP system, hoses, or charcoal canister; can also result from a loose gas cap.


• P0401 – Exhaust Gas Recirculation (EGR) Flow Insufficient Detected: EGR valve, passages, or control system problems.

Codes vary by manufacturer, and some vehicles use manufacturer-specific subcodes. If a code is unfamiliar, consult the repair manual for your exact make and model or seek a technician’s interpretation.

Drive cycle and readiness monitors

After clearing codes, the vehicle’s onboard monitors must run tests to verify all systems are functioning within specification. Some monitors require a specific drive cycle and a number of miles to complete, including steady highway speeds and varying loads. If a fault returns or a monitor remains incomplete, the MIL may illuminate again, indicating further diagnosis is needed.

When to seek professional help

Consider professional help if you:

• Cannot identify or repair the root cause after reading the codes.


• Have repeated codes after clearing, or the MIL returns shortly after a reset.


• Notice symptoms such as rough running, reduced power, rough shifting, fuel smell, or unusual noises.


• Deal with emissions-related codes that could affect your vehicle’s compliance or reliability.

In these situations, a certified mechanic or dealership can perform advanced diagnostics, including live data analysis, scan tool testing, and component-level inspections.

Safety, legality, and best practices

Clearing codes is a diagnostic step, not a workaround. Always fix the underlying fault before erasing codes. For vehicles used in regions with strict emissions testing, ensure the repairs are complete and the monitors run to completion so the vehicle passes any required inspection.

Summary

Clearing a check engine light code is a straightforward process using an OBD-II scanner, but it only hides the problem if the fault remains unresolved. Start by reading and understanding the codes, perform or arrange the necessary repairs, then erase the codes and monitor the vehicle to ensure the issue is fully resolved. Remember that readiness monitors may require a drive cycle to reset, and if the light comes back on, reassess the fault or seek professional help.

How to clear a check engine light without a scanner?

You can try to clear a check engine light by disconnecting the negative terminal of your car's battery for about 15 minutes, which will reset the engine's computer. Alternatively, for newer cars, some problems may clear themselves after driving for a few days, or you may be able to use the ignition key method of turning the ignition on and off several times, though this is not a reliable way to clear the light. Remember that if the underlying issue is not fixed, the light will likely return, so it's essential to address the cause of the warning. 
Method 1: Disconnect the battery 
This video demonstrates how to disconnect the negative battery terminal to reset the check engine light: 53sHelpful DIYYouTube · Mar 22, 2020

1. Turn the car off. Ensure the ignition is completely off. 
2. Locate the negative battery terminal. It's usually marked with a minus sign (-) and a black cable. 
3. Loosen the negative terminal clamp: with a wrench and carefully remove the negative cable. 
4. Wait for at least 15 minutes: to allow the system to fully discharge. 
5. Reconnect the negative cable: and tighten it securely. 
6. Start the car: to see if the check engine light has turned off. 

Method 2: Use the ignition key sequence (less reliable) 

• Insert the key, turn it on for two seconds, then turn it off for two seconds.
• Repeat this cycle two to four times.
• Some vehicles may reset the light this way, but it is not guaranteed to work for all issues. 

Method 3: Drive the car

• For some minor issues, the light may turn off on its own after the car has been driven for a while and the onboard computer has completed its diagnostic cycle, which can take about 50-100 miles. 

Important considerations

• The light will come back on: if the original problem is not fixed. 
• Disconnecting the battery may reset other settings, such as radio presets, clock, and other personalized settings on modern cars, which you will need to re-enter. 
• Be cautious: when working with car batteries. If you are not comfortable, have a professional do it for you. 

Can AutoZone clear engine codes?

Yes, AutoZone can read and clear engine codes for free using their Fix Finder service, but whether they will actually clear the code can vary by location due to state regulations and company policy. They will read the code, provide you with information about the potential problem, and recommend solutions, but their official policy is often to read the code rather than clear it. Some employees may clear it, especially if you've purchased parts to fix the problem. 
How the service works

• Free Scan: You can drive to any AutoZone store during business hours and an employee will use a handheld scanner to read the trouble codes from your vehicle's On-Board Diagnostics (OBD-II) port. 
• Diagnosis and Report: The service provides a report with the code's meaning and potential solutions, which can be very helpful for DIY repairs. 
• Clearing the code: The company's official stance is that they should not clear the code because a mechanic needs the code to properly diagnose the issue, and state laws in some places may prohibit it. However, some employees may clear the code for you, particularly if you have fixed the problem yourself. 

What to do

• Visit a store: Go to your local AutoZone and ask for the free Fix Finder service. An employee will come out to your car and read the codes for you. 
• Get the report: Ask for a printout of the report, which will give you detailed information on the potential problem and recommended fixes. 
• Ask about clearing: If you have fixed the problem yourself, you can politely ask if they can clear the code for you, though be prepared if they say no. 
• Consider a scanner: If you find yourself needing to clear codes often, you can purchase an affordable OBD-II scanner from AutoZone.com or another retailer, which allows you to scan and clear codes yourself. 

How to clear a check engine light with a code reader?

Side. Once it's connected you're able to read your codes. Then use the red erase button to clear your codes. So you've gone ahead and checked your codes. And cleared them but what do you do with this.

Can I reset the check engine light myself?

Yes, you can reset the check engine light yourself, but it is important to first address the underlying problem. You can reset it by disconnecting the negative battery terminal for about a minute, pulling the correct fuse, or using an OBD-II scanner to clear the code. The light will likely come back on if the issue is not fixed, and resetting it may also clear your radio presets and other vehicle settings. 
Methods to reset the light
1. Disconnect the battery 
{
"textFragment": "This video demonstrates how to reset the check engine light by disconnecting the battery:",
"video": {
"results": ["vid3"],
"size": "hero"
}
}
This is a common method, but it can reset other electronic settings in your car. 

• Turn off the car and remove the key.
• Locate the negative battery terminal (usually black with a minus sign).
• Use a wrench to loosen the nut on the terminal and pull the cable off.
• Leave the cable disconnected for 30-60 seconds.
• Reconnect the cable and tighten the nut.
• Start the car to see if the light is off.

2. Use an OBD-II scanner 

• Purchase or borrow an OBD-II scanner. Many auto parts stores will scan it for free. 
• Locate the OBD-II port, usually under the dashboard on the driver's side. 
• Plug in the scanner and turn the ignition to the "on" position (without starting the engine). 
• Follow the scanner's instructions to read and then clear the error codes. 

3. Remove the fuse 

• This method is more effective on older vehicles. 
• Locate your fuse box and find the fuse for the Engine Control Unit (ECU) or Engine Control Module (ECM). 
• Use the fuse puller or needle-nose pliers to remove the fuse. 
• Wait for 10-15 minutes, then reinsert the fuse. 

Important considerations

• The underlying problem remains: Disconnecting the battery or clearing the code does not fix the issue. If the problem persists, the light will turn back on. 
• Prepare for smog checks: Clearing the code can reset your vehicle's readiness monitors, which is necessary for passing an emissions test. It may take several days of driving to reset these monitors. 
• Be careful: Do not use a scanner to try and "jump" the diagnostic port. This can damage your car's computer.