First, check whether it's flashing
- Your car has detected a problem in a monitored engine or emissions system.
- Flashing while the engine runs, or shaking, power loss, overheating, smoke, or a fuel or burning smell? Stop safely and get help.
- Steady light and normal driving? Follow your car's warning instructions and book a diagnosis soon.
- Just filled up? A loose fuel cap is worth checking, unless there's fuel smell, a leak or heat.
- Save the code report. Don't clear the codes or disconnect the battery before the car is diagnosed.
Your car's onboard diagnostic system has spotted a problem in a monitored engine or emissions system, sometimes before you feel anything. We'd check whether the light is steady or flashing first, because its behavior and the way the car feels determine your next move.
| What you notice | What it can signal | What to do |
|---|---|---|
| Flashing while the engine runs | A possible misfire | Stop safely and get help before continuing. |
| Any light with shaking, power loss, heat, smoke or an unusual smell | A problem needing urgent attention | Stop safely and describe the symptoms when you call for help. |
| Steady light and normal driving | A detected engine or emissions problem | Follow your car's warning instructions and book a diagnosis soon. |
| Brief light or flashes before startup | An ignition or emissions self-check on some cars | Note whether it goes out after startup and check your car's warning instructions. |
It's flashing, or the car is running badly
A flashing light while the engine runs can mean a misfire that can damage the catalytic converter, even before you feel the engine running badly. Don't keep driving to see whether the warning clears.
How the car behaves matters even when the light is steady. Shaking, power loss, overheating, smoke, an unusual smell or another urgent warning calls for stopping safely and getting help.
- Ease off hard acceleration as you move out of traffic. Stop once you've reached a safe place clear of traffic.
- Follow your car's shutdown instructions. If you suspect a fire, follow the fire steps below.
- Call roadside assistance or a repair shop before the car goes anywhere else. Describe whether the light flashed with the engine running, any shaking or power loss, and any heat, smell, smoke, unusual noise or other warning. Ask whether it needs a tow. If the light flashed with the engine running or the symptoms haven't gone away, leave the car parked while you arrange the next move.
If you suspect a vehicle fire, stop and turn off the engine if you can do so safely. Get everyone out, move at least 100 feet from the car and away from traffic, and call 911. Don't open the hood or trunk if you think the fire is inside.
The U.S. Fire Administration's vehicle fire safety advice (opens in a new tab) covers what to do if your car catches fire.
It's steady and the car feels fine
- Check the warning instructions for your exact car and follow any message on the dash. There's no universal safe driving distance, speed or waiting time for a car with this warning on.
- Book a diagnosis soon, even if acceleration and the sound of the engine seem unchanged. On a 2018 Ford Escape, continuing to drive with the service engine soon light on can raise emissions, reduce fuel economy and lead to more costly repairs, even without obvious symptoms.
- If you're unsure about driving to the shop, call before setting out. Tell them about other warnings or changes in how the car behaves, and ask how they want you to bring it in. Keep your observations to what you can see from the driver's seat instead of opening the hood or approaching hot parts. If the light starts flashing or urgent symptoms appear, stop safely and use the steps above.
For a steady light with no change in how the car runs, the next checks are a fitted fuel cap when appropriate and a code report for diagnosis. Keep watching for the symptoms that change that plan, including shaking, power loss or the light starting to flash.
Check the actual warning symbol, too. Oil pressure, high temperature and charging warnings have their own instructions. On a 2025 Mazda CX-5, each has its own directions to stop driving, so report those warnings when you call.
It came on before you started the engine
A check engine light that briefly illuminates during the ignition self-check can be normal. Some cars also use flashes before startup to show that their emissions self-checks aren't complete, including the US 2018 Ford Escape. Keep that separate from a light that continues flashing with the engine running.
While safely parked, write down when you saw it. Was the engine running, did the light go out after startup, or did it stay on or keep flashing? Those details give the shop a clearer description than simply saying the light blinked.
Record the exact symbol or words, such as an engine outline, “check engine” or “service engine soon,” along with any accompanying message. Compare them with your car's warning-light instructions, including any explanation of blink counts or separate powertrain warnings.
A maintenance reminder has a different job. On a 2025 Mazda CX-5, the wrench indication can mean scheduled maintenance or an oil change is due. If you're wondering whether the engine light is asking for an oil change, identify the symbol before looking for reset instructions.
It came on after you filled up
If the light is steady, the car feels normal and you've just refueled, check the fuel cap if your car has one. On a 2025 Mazda CX-5, a missing or insecure cap can trigger the check engine light. On a 2018 Ford Escape, a fuel fill inlet that didn't close properly can also turn it on.
CX-5 owners can check the fuel-cap instructions (opens in a new tab) before handling it.
- Park safely and switch the car off before checking. Look for a removable cap that's missing or visibly loose. If your car has a capless filler, skip the cap check and arrange diagnosis.
- If a removable cap is loose, secure it using the instructions for your car. Leave a correctly seated cap alone. On a 2025 Mazda CX-5, pull the remote fuel-filler lid release to open the lid, turn a loose cap clockwise until you hear a click, then press the lid shut until it locks. Other cars can close differently.
- Note whether the cap was loose or already secure. Tightening a loose cap may not switch the warning off immediately. On the CX-5, the separate fuel cap warning can remain on until a number of driving cycles have been completed. Check your own car's instructions for what happens after correcting the cap, and book a diagnosis if it was already secure.
A missing or damaged cap needs the specified replacement, so check the requirements for your exact car.
What could be causing the warning?
Start with what you observed. Here's what can set it off, starting with what you can check while parked:
- Fuel level or filler: On a 2025 Mazda CX-5, a very low fuel level or a missing or loose cap can turn on the light. On a 2018 Ford Escape, running out of fuel or a fuel fill inlet that didn't close properly can do it.
- Fuel quality or water: On a 2018 Ford Escape, poor fuel quality or water in the fuel can bring on the warning.
- Electrical or emissions trouble: A 2018 Ford Escape can show the warning after deep water wets its electrical system. On a 2025 Mazda CX-5, an engine electrical or emissions control problem can also turn it on.
- Misfire: A poorly performing spark plug can cause a misfire you may not feel.
After checking the fuel level and a fitted cap, give the shop your observations and saved codes so a technician can test the cause.
Ask what the scan and diagnosis include
A trouble code records a condition the car detected or an area where it found a problem. It gives the technician a starting point for vehicle-specific testing. That testing should confirm the cause before a part is replaced.
We'd ask for the findings behind a repair recommendation before approving the work. Start by finding out if you're being offered a code scan, diagnostic testing or a repair, because each gives you something different.
| Stage | What you get | What to ask |
|---|---|---|
| Code scan | The exact codes and, depending on the tool, their status and other stored data. | Can you provide every complete code, its status and any freeze-frame data? |
| Professional diagnosis | Inspection and testing on your specific car to find the cause. | What is the diagnostic fee, and which vehicle-specific tests does it include? |
| Repair | Work supported by the diagnostic findings, followed by a check that it worked. | Which finding supports this work, and how will you confirm the original problem is fixed? |
Keep the code report with the repair recommendation so you have both the recorded fault and the shop's explanation. If the description names a sensor or another component, ask how the testing established what needs replacing.
Before approving an expensive emissions repair, ask the dealer to check your warranty booklet and coverage for your VIN. Confirm the covered part, your eligibility and the terms before authorizing paid work.
Will a code scan tell me which part to buy?
It gives you the recorded condition or problem area. Ask which vehicle-specific tests support a part replacement before approving it.
Could an emissions repair be covered by a longer warranty?
On eligible light-duty vehicles, catalytic converters, the emissions control computer and the OBD computer are covered for the first 8 years or 80,000 miles, whichever comes first. Ask the dealer to check the part and your VIN before you approve paid work.
Save the report before anyone clears the codes
Leave the codes alone until the car is diagnosed. Erasing them also removes freeze-frame and manufacturer-specific data a technician can use, and resets emissions readiness monitors. Those monitors return to a no-run condition, which matters when the car is due for an emissions inspection.
Don't disconnect the battery to switch the light off. That can also remove stored evidence and reset readiness. On a 2025 Mazda CX-5, Mazda warns that disconnecting and reconnecting the battery cables with the check engine light on could damage the engine and start a fire.
While safely parked, make a note for the shop with the details you already have. Include the warning's behavior and any recent events, even if the light later goes out.
- Your car's year, make, model, powertrain and mileage.
- When the warning started, whether the engine was running, and whether the light was steady or flashing.
- Any shaking, power loss, heat, smoke, smell, unusual noise or other dashboard warning.
- Recent refueling or repairs, checks you've made, the code report, and whether anyone has already cleared the codes.
Give those details to the repair shop and ask how they want the car brought in. If the light flashed while running or you noticed urgent symptoms, describe those before arranging the trip.
The light went off on its own
Keep your notes and code report after the light goes off. Codes and related data can remain stored, and the symptoms you noticed still help the shop diagnose the problem. Tell them both when the warning appeared and that it later disappeared.
If an emissions inspection is coming up, check the requirements for your vehicle and location. The light is only part of that check; readiness status matters too, and clearing codes resets those monitors.
On vehicles that support permanent trouble codes, only the OBD-II system can clear them after confirming that the fault is no longer present. California drivers can check the emissions test requirements (opens in a new tab) for how those codes and readiness checks affect their inspection.
Ask the shop to diagnose the recorded problem, confirm any needed repair worked, and keep the report with your service records.
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