Key takeaways
Fix the fault first, then clear the codes with an OBD2 scan tool with the ignition on and the engine off, or let the light go out on its own after three trips in a row without the fault. Disconnecting the battery also clears stored codes, but it wipes learned settings, and Mazda warns against it while the light is on.
- 01Never clear a flashing light: Ram's owner's manual says a flashing light means severe catalytic converter damage and power loss will soon occur.
- 02Clearing erases the freeze frame and pending codes and resets the readiness monitors, so a car cleared just before an emissions test is likely to be turned away.
- 03Permanent codes, phased in from the 2010 model year, survive a scan tool or battery reset and clear only after the monitor reruns and passes.
- 04AutoZone, O'Reilly and Advance Auto Parts read codes for free, while RepairPal puts a shop diagnosis at $125 to $183.
This guide belongs to our OBD2 guide: first steps section, which covers the wider topic.
The right way to clear a check engine light is to fix whatever turned it on, then erase the codes with an OBD2 scan tool. AutoZone's reset guide says to reset the light only after the underlying issue is fixed, and lists a battery disconnect, a fuse pull and several days of normal driving as other ways to turn it off.
Knowing when not to clear the light saves money, because a clear wipes the freeze frame data a technician relies on, resets the readiness monitors and, on many 2010 and newer cars, can leave a permanent code an inspection still sees.
If you haven't read the code yet, start with our checklist for what to do when your check engine light comes on, then come back once you know what the car stored.
Clearing a Check Engine Light: The Quick Answer
Use a scan tool after the repair, or let the car turn the light off by itself once the fault is gone. Disconnecting the battery is the last resort.
| Method | How it works | Hands-on time | Best for | Main drawback |
|---|---|---|---|---|
| Scan tool clear (Mode $04) | Sends a clear command through the OBD2 port | A few minutes | Confirming a finished repair | Erases freeze frame, resets monitors |
| Fix it and let it self-clear | Light goes out after three trips in a row without the fault | None, but it takes days | A gas cap or other repair already made | Slow; the code stays in memory a while |
| Battery disconnect | Cuts power to the car's computers | About 15 minutes | No scanner available | Loses radio presets and learned settings |
| ECU fuse pull | Cuts power to the engine computer | 10 to 15 minutes | An alternative to the battery method | Pulling the wrong fuse can disable other systems |
Methods and wait times from AutoZone's reset guide. Self-clear rule from EPA's OBD regulations. Scan tool effects from Snap-on's OBDII service mode guide.
Tools and Information You Need First
You need a way to read and clear codes, plus a record of everything the car stored before you erase it.
- An OBD2 reader, scan tool or phone app with an adapter, or a free parts store scan
- Your phone or a notebook to record the codes, freeze frame and readiness status
- Your owner's manual, for the port location, drive cycle and items to reset after a battery disconnect
- Your radio's anti-theft code, if the car uses one
- A wrench, safety glasses and gloves, only if you plan to disconnect the battery
Even a basic reader can erase codes, but only a tool with freeze frame and I/M readiness screens shows what you're about to lose and when the car is ready for inspection. Our guide to the best OBD2 scanners compares readers from about $20 with pro-grade tools.
Time and Difficulty
Clearing codes is a beginner job. The waiting comes afterward, while the car reruns its self-tests.
| Task | Difficulty | Time |
|---|---|---|
| Reading codes at a parts store | Easy | Often under a minute once the reader is plugged in |
| Clearing codes with a scan tool | Easy | A few minutes |
| Battery disconnect | Easy | About 15 minutes off, per AutoZone; 30 to 60 seconds, per two dealers |
| Readiness monitors resetting | Hands-off | About a week of normal driving, per CARB |
Times from AutoZone, Honda of Kirkland, Bowman Chevrolet and the California Air Resources Board.
How to Clear Check Engine Light Codes With a Scan Tool
It's the cleanest method, because it clears the diagnostic memory without cutting power to the rest of the car. Identifix's repair guidance tells technicians to clear a code with a scan tool after the root cause is repaired and the required data is saved.
- Park with the engine off and find the port. AutoZone says it's usually under the dashboard.
- Plug in the scanner and turn the ignition on without starting the engine. x-engineer's Mode $04 explainer notes that engine computers must answer a clear request with the ignition on and the engine off.
- Record every code. Identifix says to record all stored, pending and permanent codes before clearing anything.
- Save the freeze frame and readiness screens. Photograph them if your tool can't store them.
- Look up each code. Our free OBD2 Code Lookup gives a code's meaning, likely causes and whether it's safe to keep driving.
- Make the repair.
- Choose Erase Codes or Clear DTCs and confirm.
- Turn the ignition off, then start the engine to check that the light stays off, as AutoZone advises.
- Drive normally for several days, then check readiness again.
Letting the Light Go Out on Its Own
Once the fault is fixed, the car turns the light off by itself after three clean trips in a row, with no tool needed.
EPA's 1995 OBD rule lets the light go out if the malfunction doesn't recur during three subsequent sequential trips in which the monitor runs. For fuel system and misfire faults, those trips also need engine speed within 375 rpm, load within 10 percent and the same warm-up status as when the fault was found.
Our P0171 system too lean guide covers how that rule applies to lean codes.
The stored code outlasts the light. California's OBD II regulation lets the computer erase a confirmed code only after 40 warm-up cycles without the fault, so it can still show on a scan after the light is off.
The EPA's first check for a steady light is the gas cap. Its check engine light fact sheet says to have the car serviced if the light doesn't go out after a few short trips once the cap is tightened or replaced, and Bowman Chevrolet puts that at about 10 to 20 miles.
The leak test behind a gas cap code runs only under certain conditions, which our P0455 large EVAP leak guide walks through. Until it runs and passes, the light stays on.
Some dealer blogs, such as Peters Chevrolet's reset tips, say turning the ignition on and off about three times resets codes. The federal rule counts trips in which the monitor runs and finds no fault, so drive normally instead.
How to Clear Codes by Disconnecting the Battery
It clears codes on many cars, but it also wipes settings the car has learned. Mazda's CX-50 owner's manual tells owners not to do it at all while the check engine light is on or flashing.
Check your manual before you pull a battery cable
Mazda warns that disconnecting the battery cables while the check engine light is on or flashing can damage the engine when the cables are reconnected, which could result in a fire. If your manual has a similar warning, use a scan tool.
- Record the codes and freeze frame first.
- Find your radio code. Bernardi Parts, a Honda dealer's parts site, says a Honda radio typically locks after a battery disconnection and shows ENTER CODE or CODE, and many Hondas carry the code on a glove box sticker.
- Turn everything off, remove jewelry and put on safety glasses and gloves.
- Loosen the negative (−) terminal and lift the cable off. Honda of Kirkland's reset guide says to keep the cable from touching other parts to avoid sparks.
- Wait. AutoZone says about 15 minutes, while Bowman Chevrolet's reset guide and Honda of Kirkland say 30 to 60 seconds. Honda of Kirkland also has a helper sound the horn to drain leftover power.
- Reconnect and tighten the negative cable.
- Start the car and reset what was lost.
Kia's 2025 reset items list shows what else goes: after a battery disconnect, owners reset the auto up and down windows, sunroof, driver's seat position, climate control, trip computer, radio presets and clock.
The engine computer loses learned data too. California's OBD II regulation says keep-alive memory may be erased if power to the control unit is interrupted, for example by a disconnected battery or a removed fuse, and Identifix warns that a battery disconnect may create extra relearn work.
AutoZone's other option is pulling the ECU or ECM fuse named in your owner's manual for 10 to 15 minutes, with a warning that the wrong fuse could disable other systems for a while.
What Clearing the Codes Erases
A clear command wipes far more than the light. It also resets inspection readiness, but it can't touch a permanent code.
| Data | What it tells you | After a clear |
|---|---|---|
| Confirmed trouble codes | The faults that turned the light on | Erased |
| Pending codes | Faults seen once but not yet confirmed | Erased |
| Freeze frame | Engine conditions when the code set | Erased |
| Monitor test results (Mode $06) | How each self-test scored | Erased |
| Readiness monitors | Whether each emissions self-test has finished | Reset to Not Ready |
| Distance and time since codes cleared | How long ago the memory was wiped | Reset |
| Permanent codes (phased in from 2010) | Faults that turned the light on | Kept until the monitor reruns and passes |
From Snap-on's OBDII service mode guide, x-engineer's Mode $04 explainer, California's OBD II regulation and California's Bureau of Automotive Repair.
Snap-on's OBDII service modes guide says Mode $04 clears DTCs, freeze frame data and monitor test results, resets the monitors to Not Ready and turns the light off.
Pending codes are early warnings. California's regulation has the computer store one within 10 seconds of detecting a fault and erase it if the fault isn't seen again by the end of the next drive in which the monitor runs.
Why freeze frame data matters
Underhood Service's freeze frame article describes it as a snapshot of sensor readings when the code sets, which helps a technician recreate the fault on a test drive. Identifix lists clearing codes before saving it among the common diagnostic mistakes.
Permanent codes since 2010
California's regulation phased permanent codes in on 50 percent of 2010, 75 percent of 2011 and all 2012 and newer vehicles. Snap-on notes they're read through a separate service, Mode $0A.
The Bureau of Automotive Repair's permanent code article says they can't be reset by disconnecting the battery or cleared with a scan tool. The only way to clear one is to fix the problem and drive until the monitor that found it runs again without finding a fault.
When Should You Not Clear the Codes?
Don't clear codes when the light is flashing, before the fault is diagnosed, in the days before an emissions test, or while a warranty might pay for the repair.
When the light is flashing
Ram's owner's manual says that if the light is flashing, severe catalytic converter damage and power loss will soon occur, and immediate service is required. Clearing the code doesn't stop the misfire behind it.
AAA's check engine light guide says to pull over immediately and shut off the engine if the light is flashing, the car drives abnormally, or you notice smoke or strange odors.
Our guide to a flashing check engine light covers the causes and whether it's safe to keep driving.
Before anyone has diagnosed it
Clearing first throws away the clues. RepairPal's diagnosis estimate describes a technician reading the stored codes, checking service bulletins and testing the suspect parts, then clearing the codes after the repair and test-driving the car.
Four Car Garage's reset article adds that an intermittent fault, such as a small EVAP leak, can take longer to bring the light back once it's cleared.
In the days before an emissions test
A fresh clear leaves the monitors Not Ready, which inspection programs treat as a reason to turn the car away. Ohio EPA's readiness guide asks anyone working on a car before or after an E-Check not to clear the codes when possible, so the light can show whether the repair worked.
While the car is under warranty
Federal emissions warranty law covers 1995 and newer cars and light trucks for 2 years or 24,000 miles, and the catalytic converter, electronic emissions control unit and onboard emissions diagnostic device for 8 years or 80,000 miles. Let the dealer see the stored codes and freeze frame first.
EPA's emission warranty rule uses the same two periods, and its 8-year, 80,000-mile list includes catalytic converters and the emission control module.
Free tool
Check Engine Light Checker. Pick steady, flashing or came on then went off, tick a red oil or temperature warning, rough running or a recent fill-up, and get a Low risk, Act soon or Stop and check ruling before you decide whether to clear anything.
If you're unsure how urgent the light is, run the Check Engine Light Checker first, since it works from the light and your symptoms rather than the code.
How Long Do Readiness Monitors Take to Reset?
Usually a few days to about a week of normal mixed driving. The CARB OBD II fact sheet tells drivers to drive as they normally do for about a week or so, and Ohio EPA says at least two or three days, or longer on older vehicles.
Cars may run up to 11 self-tests. The NYVIP3 readiness monitor overview says misfire, fuel system and comprehensive component monitors run constantly, while catalyst, EVAP, oxygen sensor, sensor heater, EGR and secondary air monitors need set conditions, some over two drive cycles.
The EVAP leak test shows why it takes time. New York's EVAP monitor page says it needs a tank 1/4 to 3/4 full, temperatures between 30°F and 95°F, no EVAP codes stored and a car that has sat overnight or for at least 8 hours.
| Source | Before you start | The drive |
|---|---|---|
| Ford owner's manual | Engine off at least 8 hours, then warm up | 15 minutes of steady highway driving, then 20 minutes of stop-and-go with at least four 30-second idles, without switching off |
| GM, via Ohio EPA | Cold start, coolant below 122°F and within 11°F of outside air | Idle 2.5 minutes with A/C and rear defroster on, 55 mph for 3 minutes, coast to 20 mph without braking, back to 55 mph for 5 minutes, coast to 20 mph |
| Honda, via Ohio EPA | Tank about 3/4 full, parked 6 hours or more, 40°F to 95°F outside | Hold 2,000 rpm until the gauge reaches 1/4, at least 20 minutes at 50 to 60 mph without cruise control, at least 10 minutes in town, then park 30 minutes |
Ford from its owner's manual. GM and Honda (2009 Honda Accord and 2010 Acura TSX owner's manuals) as compiled by Ohio EPA. Drive cycles vary by model, so check your own manual and obey all traffic laws.
You can often check readiness without a scanner. Ford's owner's manual says to switch the ignition on for 15 seconds without cranking: eight flashes of the light means not ready, and a steady light means ready.
Ohio EPA says a Chrysler, Dodge or Jeep light that flashes for about 10 seconds and then stays lit means not ready. It adds that a GM catalyst monitor may take up to five full cycles if the converter is marginal or the battery was disconnected.
Can You Clear Codes Right Before an Emissions Test?
You can, but it backfires. Inspection equipment reads the readiness monitors, so a freshly cleared car usually gets turned away, and in California a permanent code can fail it anyway.
The federal inspection rule, 40 CFR 85.2222, lets 1996 to 2000 vehicles pass with two or fewer unset monitors and 2001 and newer vehicles with no more than one. A car with too many is sent away to be driven and fails if they're still incomplete at the retest.
| Program | What recently cleared codes lead to |
|---|---|
| Federal I/M rule | Return after driving; fail if monitors are still unset at retest |
| New York | No pass; a 10-day extension only if not ready was the sole failure and the old inspection had expired |
| New Jersey | A light turned off to pass is a listed cause; the car is rejected |
| Texas | Two or more Not Ready monitors on a 2001 or newer car fails |
| California | A permanent code on a 2010 or newer car fails Smog Check |
From 40 CFR 85.2222, the New York DMV, the New Jersey Motor Vehicle Commission, the Texas Department of Public Safety and California's Bureau of Automotive Repair. Rules change, so check your own state's program.
New Jersey's readiness brochure lists a check engine light turned off in an attempt to pass inspection among the causes of a readiness failure, along with a battery replaced within the last month. Those cars are rejected, must complete a drive cycle and then have to pass a reinspection.
The New York DMV's readiness guide lists codes cleared during recent repairs as a cause of a not ready result. It says most cars need two drive cycles separated by a cool-down period, with the tank half to three-quarters full.
California shows how often it backfires. BAR added permanent codes to the Smog Check failure criteria for 2010 and newer vehicles on July 1, 2019, and in the first month 3,124 vehicles that would have passed before failed on them, all with recent codes cleared. In BAR's follow-up, 63.2 percent of them passed once the computer cleared the permanent code on its own, and 7.2 percent failed again.
BAR ignores a permanent code only after 15 warm-up cycles and 200 miles since the codes were last cleared, a limit meant for cars that struggle to finish their monitors.
Is it illegal? The state guides cited here treat a recently cleared car as not ready to test rather than naming a penalty, and O'Reilly says customers may clear codes themselves except where prohibited by law.
Where to Get Codes Read for Free
AutoZone, O'Reilly and Advance Auto Parts read check engine codes for free, so the first step costs nothing.
- AutoZone: AutoZone's Fix Finder test often takes less than a minute once the reader is plugged in, and the printed and emailed report includes emission readiness.
- O'Reilly: O'Reilly's free VeriScan testing covers 1996 and newer vehicles, since older OBD-I cars need different tools, but staff are not allowed to clear the codes causing the light.
- Advance Auto Parts: Advance's store services page offers free code scanning on most OBD II vehicles, though services vary by vehicle and location.
Mistakes to Avoid When Clearing Codes
Most clearing mistakes cost you information, an inspection trip or a repair bill.
- Clearing before recording. The codes and freeze frame are gone for good.
- Clearing a flashing light and driving on. The misfire keeps damaging the converter.
- Clearing in the week before an inspection. The monitors won't be ready.
- Disconnecting the battery against the manual's advice. Mazda warns of engine damage and a possible fire.
- Clearing the same code over and over. AutoZone compares resetting without a fix to putting tape over a warning light.
What It Costs to Clear a Check Engine Light: DIY or Shop
Clearing is free once you own a reader. Diagnosis and repair are where the money goes.
| Option | Typical cost | Notes |
|---|---|---|
| Free scan at AutoZone, O'Reilly or Advance | $0 | O'Reilly staff won't clear the codes |
| Basic OBD2 code reader | $19.99 to $22.99 | Reads and clears codes |
| Scan tool with ABS, SRS or bidirectional features | $119.99 to $379.99 | Adds live data and more systems |
| Shop code read | Around $100, or about an hour of labor | O'Reilly's estimate |
| Check engine light diagnosis | $125 to $183 | RepairPal national estimate |
| Emissions warranty repair | Covered by the carmaker | Converter, engine computer and OBD device for 8 years or 80,000 miles |
Reader and scan tool prices from the models in CarTipsMentor's Best OBD2 Scanners guide. Shop code read from O'Reilly. Diagnosis from RepairPal, updated September 3, 2026, before taxes and fees. Warranty terms from 42 U.S.C. 7541 and 40 CFR 85.2103.
RepairPal's range doesn't factor in your location. AAA's 2026 labor rate guide says almost half of all shops charge $120 to $159 an hour, and dealers often charge 25 percent or more above independents.
The order that saves money is simple: read the code, write it down, fix the cause, clear it, then give the car a week of normal driving before any inspection.
Frequently Asked Questions
How many miles do you have to drive to reset the check engine light?
There is no single number. Federal OBD rules let the light go out after three trips in a row in which the monitor runs without finding the fault, and Bowman Chevrolet puts a gas cap fix at about 10 to 20 miles. For readiness, CARB suggests about a week of normal driving. California ignores a permanent code at Smog Check only after 200 miles and 15 warm-up cycles since clearing.
Why does the check engine light come back after clearing the codes?
Clearing erases the record, not the fault. If the leak, misfire or failed sensor is still there, the next self-test fails and the light returns. Four Car Garage, a California repair shop, says a constant fault such as a completely failed sensor usually brings the light back right away, while an intermittent fault such as a small EVAP leak takes longer.
Can an auto parts store clear my check engine light?
Don't count on it. O'Reilly says its staff are not allowed to clear the trouble codes behind the light, though customers may clear them themselves except where prohibited by law. AutoZone and Advance Auto Parts offer free code reads too, but their service pages don't promise a clear. Keep the printed or emailed report so you have a record of the codes before anything is erased.
What does a solid orange check engine light mean?
A steady light means the engine computer has found a fault and stored a code. The EPA says there is no cause for panic and that the car is telling you to seek attention soon, starting with a check of the gas cap. Mazda lists engine, emission and transmission control problems, a very low fuel level and a loose or missing fuel cap as causes.
Is it safe to drive with the check engine light on?
Usually for short distances, if the light is steady and the car drives normally. AAA says that is OK as long as nothing is noticeably wrong, and Ram's manual says the vehicle should be serviced if the light stays on through several typical driving styles. If the light flashes, the car runs badly, or you notice smoke or odd smells, AAA says pull over and shut the engine off.
Do you need to clear the codes after a repair?
Not always. The EPA says that once the problem is addressed, the OBD computer turns the light off on its own. RepairPal describes technicians resetting codes after a repair and test-driving to confirm the fix. Letting the light go out by itself avoids one cause of a not ready inspection result that the New York DMV lists: codes cleared with a scan tool during recent repairs.
Sources and References
- AutoZone. How to Reset Your Check Engine Light
- AutoZone. Fix Finder by AutoZone: Free Car Diagnostic Tool
- O'Reilly Auto Parts. Free Check Engine Light Testing: No Appointment Needed
- Advance Auto Parts. Free Store Services
- Snap-on. OBDII Service Modes
- x-engineer. OBD Diagnostic Service (Mode) $04: Clear/Reset Emission-Related Diagnostic Information
- Identifix. P0171 Code: Causes, Symptoms, and How to Fix It
- Underhood Service. Freeze Frame Diagnostics
- U.S. EPA (Federal Register). Regulations Requiring On-Board Diagnostic Systems: Revision to Requirements for Storage of Engine Conditions Associated With Extinguishing a Malfunction Indicator Light (August 2, 1995)
- U.S. EPA. Check Engine Light and OBD Consumer Fact Sheet (Office of Transportation and Air Quality)
- U.S. EPA (eCFR). 40 CFR 85.2222: Onboard Diagnostic Test Procedures
- U.S. EPA (eCFR). 40 CFR 85.2103: Emission Warranty
- Legal Information Institute (Cornell Law School). Cal. Code Regs. Tit. 13, Section 1968.2: Malfunction and Diagnostic System Requirements, 2004 and Subsequent Model-Year Vehicles
- Legal Information Institute (Cornell Law School). 42 U.S. Code Section 7541: Compliance by Vehicles and Engines in Actual Use
- California Air Resources Board. On-Board Diagnostic II (OBD II) Systems Fact Sheet
- California Bureau of Automotive Repair. Permanent Diagnostic Trouble Codes (Automotive Repair and Smog Check News, Fall 2019)
- New York State DMV. What Do You Mean My Car's Not Ready?
- New York Vehicle Inspection Program (NYVIP3). OBD II Readiness Monitors Overview
- New York Vehicle Inspection Program (NYVIP3). EVAP System Monitor
- New Jersey Motor Vehicle Commission. Preparing for OBD Inspection: Avoiding OBD Readiness Failure
- Texas Department of Public Safety. Ready or Not
- Ohio EPA (E-Check). On Board Diagnostic (OBD) Readiness and Drive Cycle Information
- Ford Motor Company. Owner's Manual: Fuel and Refueling, Emission Control System
- Mazda USA. 2025 Mazda CX-50 Owner's Manual: Check Engine Warning Light
- Kia. 2025 Kia Owner's Manual: Reset Items
- Mopar (Ram). 2022 Ram 2500/3500 Owner's Manual: Engine Check/Malfunction Indicator Warning Light
- Bernardi Parts Honda. How to Find & Enter Your Honda Radio Code
- Honda of Kirkland. How to Reset Your Check Engine Light
- Bowman Chevrolet. How to Reset a Check Engine Light
- Peters Chevrolet Buick Chrysler Jeep Dodge Ram Fiat. How to Reset Your Check Engine Light
- Four Car Garage. Can A Check Engine Light Be Reset Without Repair?
- AAA. The Check Engine Light: Common Causes and How To Fix It
- AAA. Average Mechanic Labor Rate: Repair Costs in Your State 2026
- RepairPal. Check Engine Light Diagnosis & Testing Cost Estimate
Written by
CarTipsMentor Team
Researched from the sources listed above and checked against them before publishing. Nobody paid to be mentioned on this page. It is general information, not advice about your own vehicle.
Published . Last updated .
