Learning how to clear codes on car is a useful skill for any driver. Clearing diagnostic trouble codes from your car’s computer can be done with a simple scanner, but understanding the underlying issue is key. This guide will walk you through the entire process, from reading the codes to safely resetting them and knowing when to call a professional.
Modern vehicles are packed with computers that monitor every system. When something goes wrong, a Diagnostic Trouble Code (DTC) is stored. These codes point mechanics—or you—toward the problem. While clearing the code turns off the dashboard warning light, it doesn’t fix a broken part. It’s just the first step in proper car maintenance.
How To Clear Codes On Car
The most common and reliable method for clearing codes involves using an OBD-II scanner. Since 1996, all cars sold in the United States have a standardized On-Board Diagnostics port, usually found under the dashboard near the steering wheel. This port is your gateway to the car’s computer.
What You Will Need
Before you start, gather the right tools. You don’t need expensive equipment for basic code clearing.
- An OBD-II Scanner: These range from basic Bluetooth models that pair with your phone to advanced handheld units with screens.
- Your Vehicle’s Key: You’ll need to turn the ignition to different positions.
- A Smartphone or Tablet (Optional): If using a Bluetooth/Wi-Fi scanner, you’ll need the companion app.
- Patience: The process is straightforward, but rushing can lead to missed steps.
Step-By-Step Guide To Using An OBD-II Scanner
Follow these steps carefully to read and clear your car’s trouble codes.
Step 1: Locate Your Vehicle’s OBD-II Port
The port is always within two feet of the steering wheel. Check under the dash, behind a small panel, or near the fuse box. It’s a 16-pin trapezoid-shaped connector. If you have trouble finding it, your owner’s manual will show its exact location.
Step 2: Connect The Scanner And Turn On The Ignition
Plug your scanner directly into the OBD-II port. Next, turn your ignition key to the “On” position. You do not need to start the engine. The dashboard lights should illuminate, and your scanner will power up. Wait for it to establish a link with the car’s computer.
Step 3: Read The Stored Codes
Navigate the scanner’s menu to select “Read Codes” or a similar command. The scanner will retreive all pending and confirmed trouble codes. Write these codes down. They are usually a letter followed by four numbers (e.g., P0420). This is the most important step, as it tells you what the computer has detected.
Step 4: Clear Or Erase The Codes
After noting the codes, find the menu option to “Clear Codes,” “Erase Codes,” or “Reset ECU.” Select it. The scanner will ask for confirmation. Once confirmed, you should see a message like “Codes Cleared.” Your check engine light should turn off immediately on the dashboard.
Step 5: Perform A Drive Cycle
Clearing the codes resets the monitors. To complete the process, you need to drive your car under various conditions so the computer can run its tests. This is called a drive cycle. It typically involves a mix of city and highway driving for about 30 to 50 miles. If the problem is fixed, the light should stay off.
Alternative Methods For Clearing Codes
While an OBD-II scanner is the best tool, there are a couple other ways to clear codes, though they are less reliable.
Disconnecting The Car Battery
This is a common “old school” method. Disconnecting the battery’s negative terminal for 15-30 minutes can reset the car’s computer and clear codes. However, it’s imprecise. It will also erase radio presets, clock settings, and learned engine parameters, which may cause the car to run poorly for a short time. It’s not recommended for modern vehicles with complex electronics.
Using A Smartphone App
Many affordable Bluetooth OBD-II adapters pair with apps on your phone. These apps, like Torque or OBD Fusion, provide the same code reading and clearing functions as a dedicated scanner. They are a great, low-cost option for casual use. Ensure you get a reputable adapter that is compatible with your phone’s operating system.
Understanding Diagnostic Trouble Codes
Clearing a code without understanding it is like deleting an error message without reading it. The code is a symptom, not the disease. Here’s how to make sense of them.
Code Structure And Meaning
A standard OBD-II code has five characters. The first is a letter indicating the system involved.
- P: Powertrain (Engine, Transmission)
- B: Body (Airbags, Power Windows)
- C: Chassis (ABS, Stability Control)
- U: Network & Communication (Wiring between modules)
The next four digits give specifics. The first number tells you if it’s a generic (0) or manufacturer-specific (1) code. The remaining three digits point to the exact fault. For example, a P0302 code indicates a misfire in cylinder number 2.
Common Trouble Codes You Might Encounter
Some codes appear more frequently than others. Knowing these can help you gauge the seriousness.
- P0420: Catalyst System Efficiency Below Threshold. Often points to a failing catalytic converter.
- P0442: Evaporative Emission System Small Leak Detected. A loose or faulty gas cap is a common cause.
- P0300: Random/Multiple Cylinder Misfire Detected. This can be caused by spark plugs, ignition coils, or fuel system issues.
- P0171: System Too Lean (Bank 1). The engine is getting too much air or not enough fuel.
Always research your specific code to understand potential causes and repair costs before deciding to clear it.
When Should You Clear Codes On Your Car?
Knowing when it’s appropriate to clear a code is just as important as knowing how. Here are the right and wrong reasons.
Appropriate Times To Clear Codes
- After a successful repair to verify the fix and turn off the warning light.
- After an intermittent issue that has self-corrected, like a loose gas cap, to see if it returns.
- Before an emissions test, but only if you are confident the underlying problem has been resolved. The monitors need to be in a “ready” state to pass.
When You Should Avoid Clearing Codes
- As a permanent fix for an ongoing problem. The light will just come back on.
- To sell a car without disclosing a known issue. This is unethical and often illegal.
- Immediately after the light comes on. You need to read the code first to understand the problem.
- If the car is running poorly (sputtering, stalling, loss of power). Clear codes only after diagnosing the serious issue.
What To Do After Clearing The Codes
Your job isn’t finished once the check engine light goes off. Proper follow-up ensures the problem is truly gone.
Monitor Your Vehicle’s Performance
Pay close attention to how the car drives, sounds, and feels. Does it accelerate smoothly? Is the idle rough? Note any changes. Keep a log if necessary, especially if the problem was intermittent.
Check If The Code Returns
Sometimes a code can be pending or set after several drive cycles. Use your scanner periodically over the next week of driving to check for pending codes. A pending code means the computer has seen the fault again but not enough times to turn the light back on. This is a clear sign the issue persists.
Complete The Drive Cycle For Emissions Readiness
If you need to pass an emissions test, simply clearing the code will result in a “not ready” status. You must complete a full drive cycle to allow all the emission system monitors to run their self-checks. Your scanner can usually show the readiness monitor status. Each vehicle’s drive cycle is unique; you can often find the specific procedure in the service manual.
Frequently Asked Questions
Will Clearing Codes Damage My Car?
No, clearing the codes themselves will not damage your car. It simply erases the stored fault data from the computer’s memory. However, ignoring the problem that caused the code and continuing to drive could lead to further damage.
How Long Do Cleared Codes Stay Gone?
Cleared codes are permanently erased from the computer’s memory. They will only reappear if the sensor detects the same fault condition again. If the repair was successful, the codes should not return.
Can Autozone Clear My Check Engine Light?
Yes, most AutoZone stores and similar auto parts retailers offer free code reading and will often clear the codes for you. This is a helpful service if you don’t own a scanner. Remember to ask them to write the codes down for you before they clear them.
Is It Safe To Drive With The Check Engine Light On?
It depends on the code. A solid check engine light often indicates a less urgent issue, but driving for a short period to get it checked is generally okay. A flashing check engine light signals a severe problem, like a misfire that can damage the catalytic converter. You should stop driving as soon as it is safe to do so and have the car towed to a mechanic.
Do I Need A Special Scanner For My Car Brand?
For reading and clearing generic OBD-II codes (P0xxx codes), any standard scanner will work on any 1996 or newer car. To access manufacturer-specific codes (P1xxx codes) or advanced systems like transmission or ABS, you may need a more advanced scanner or one tailored to your specific brand.
Understanding how to clear codes on your car empowers you to take an active role in vehicle maintenance. The process is simple with the right tool, but the real value lies in using the codes as a starting point for diagnosis. Always prioritize fixing the root cause over simply turning off the warning light. With this knowledge, you can communicate more effectively with mechanics, save money on unnecessary repairs, and keep your car running smoothly for years to come.