The check engine light and an oil change are usually separate issues, but low oil can trigger the light
Your check engine light turns on when your vehicle's onboard diagnostic system detects a problem with the engine, emissions system, or transmission. An oil change is routine maintenance. The two are not the same thing — but low oil pressure or an oil level that has dropped too far can cause the check engine light to illuminate, which is why you might see them happen around the same time.
If your check engine light is on and you are also due for an oil change, the light may or may not be related to the oil. The only way to know what triggered it is to read the diagnostic code stored in your vehicle's computer. A mechanic or auto parts store can do this with a code reader, usually for free or a small fee. Once you know the code, you can decide whether to change the oil first, address a separate problem, or do both.
Key Takeaways
- A check engine light can be triggered by low oil pressure or low oil level, but it usually signals a different engine or emissions problem.
- You can read the diagnostic code yourself with a code reader (available at auto parts stores or online), or have a mechanic read it for free or a small fee.
- If the code points to an oil-related issue, changing the oil and checking your oil level may turn the light off after you drive for a few miles.
- If the code points to something else — a faulty sensor, a loose gas cap, or a catalytic converter problem — an oil change will not fix it.
- Ignoring a check engine light while also skipping an oil change can damage your engine, so address both the light and your maintenance schedule.
How to read your check engine light code
The diagnostic code is a four-character alphanumeric string that tells you what system triggered the light. You do not need a mechanic to read it. Many auto parts stores (AutoZone, O'Reilly, Advance Auto Parts, NAPA) will read the code for free if you bring your vehicle to them. You can also buy a code reader online for $25 to $100 and read it yourself — plug it into the diagnostic port under your steering wheel, and it will display the code on a small screen.
Write down the exact code. Then search for it online along with your vehicle's year, make, and model. This will show you what system the code refers to. Codes starting with P0 are powertrain codes (engine and transmission). Codes starting with P1 are manufacturer-specific. Some codes are serious; others are minor. A P0171 code (system too lean) is common and can point to a bad oxygen sensor, a fuel injector problem, or low fuel pressure. A P0300 code (random misfire) can mean anything from a bad spark plug to low compression.
When low oil actually triggers the check engine light
Low oil pressure or low oil level can trigger the check engine light, but the codes that appear are specific. A P0520 code means your oil pressure sensor is reading low or has failed. A P0521 code means the oil pressure is unstable. These codes tell you to check your oil level first — if it is low, top it off and see if the light goes away after you drive for a few miles. If the level is normal, the sensor itself may be faulty and need replacement.
If you have not had an oil change in a long time, the oil may be thick and dirty enough to restrict flow, which can trigger a pressure code. In this case, changing the oil and replacing the filter will usually resolve the issue. However, if the code is something other than a pressure code, the oil change may not turn the light off. Do not assume that changing the oil will fix any check engine light — read the code first.
What to do if the code is not oil-related
If the diagnostic code points to an oxygen sensor, a catalytic converter, a mass airflow sensor, or an emissions leak, an oil change will not turn the light off. These are separate systems. You will need to have the specific component diagnosed and repaired. Continuing to drive with the light on can damage your catalytic converter or cause your vehicle to run poorly and use more fuel.
Some codes are less urgent than others. A loose gas cap can trigger a code and the light; tightening it and driving for a few miles may clear it. A faulty oxygen sensor will not damage the engine when ready, but it will reduce fuel economy. A catalytic converter problem is more serious and should be addressed sooner. Once you know the code, you can research how urgent the repair is and decide whether to handle it right away or schedule it for later.
Changing your oil while the light is on
There is no harm in changing your oil while the check engine light is on. If the light is on because of low oil pressure or low oil level, the oil change may turn it off. If the light is on for another reason, the oil change will not affect it, but you still need the maintenance. Do both: read the code to understand what triggered the light, change the oil if you are due, and then address whatever the code is pointing to.
After you change the oil, drive the vehicle for at least 10 to 20 miles before you assume the light will stay off. The onboard diagnostic system needs time to run its tests and confirm that the problem is resolved. If the light is still on after that, the issue is not oil-related and requires a separate repair.
Clearing the check engine light yourself
You can clear the check engine light by disconnecting your vehicle's battery for 15 minutes, which resets the computer. However, this only erases the code from memory — it does not fix the underlying problem. The light will come back on the next time the system detects the same issue. Clearing the code without addressing the problem is not a solution; it just hides the warning until the problem gets worse.
Some code readers also have a clear function that will erase the code without disconnecting the battery. Again, this is a temporary fix. The code will return if the problem is still there. The only way to make the light stay off is to fix whatever triggered it in the first place.
When to see a mechanic
If you read the code yourself and it points to something you are not comfortable diagnosing — a sensor, a fuel system component, or an emissions part — take your vehicle to a mechanic. Bring the code with you so they know where to start. If you do not want to read the code yourself, a mechanic can do it and explain what it means. The diagnostic fee is usually $50 to $150, though many shops will waive it if you have them do the repair.
Do not ignore the check engine light for weeks or months. The longer you drive with it on, the more damage can occur. If the light is flashing (not steady), stop driving when ready — a flashing light means a serious misfire is happening, and continuing to drive can damage your catalytic converter. Pull over safely and have the vehicle towed to a mechanic.
Frequently Asked Questions
Can I drive with the check engine light on?
Yes, if the light is steady (not flashing). A steady light means a problem has been detected but the engine is not in when ready danger. However, you should have the code read and the issue diagnosed within a few days. A flashing check engine light means a serious misfire is occurring — stop driving and have the vehicle towed.
Will changing the oil turn off the check engine light?
Only if the light was triggered by low oil pressure or low oil level. If the code points to a sensor, emissions system, or other component, the oil change will not turn the light off. Read the diagnostic code first to know whether the oil change will help.
How much does it cost to fix a check engine light?
The cost depends entirely on what triggered the light. A loose gas cap costs nothing to tighten. A bad oxygen sensor might cost $200 to $400. A catalytic converter replacement can cost $800 to $2,000. Reading the code will tell you what needs to be fixed, so you can get a repair estimate before committing to anything.
Should I change my oil before or after I fix the check engine light?
If you are due for an oil change, do both. Change the oil first if it has been a long time since your last change, then address whatever the diagnostic code is pointing to. If the code is oil-related, the oil change may resolve it. If it is not, you still need the maintenance.
What if I clear the code and the light comes back on?
The light comes back because the underlying problem is still there. Clearing the code only erases the record from your vehicle's computer — it does not fix the issue. Have the code read again and address the actual problem instead of clearing it repeatedly.