How to Diagnose & Fix a Check Engine Light after an Oil Change

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Find out why an oil change would trigger engine issues
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In theory, an oil change shouldn’t trigger a check engine light. But if the job wasn’t done right, something was knocked loose in the process, or the light needs to be reset, you could trigger a check engine light after changing the oil. It’s also possible that there is an issue with your vehicle unrelated to the oil change and timing is a coincidence. Regardless, we’ll break down what the issue could be (and even explain what to do if an oil change shop owes you one after they dropped the ball).

Causes of the Check Engine Light after an Oil Change

If the check engine light appeared immediately after the oil change, it’s likely whoever changed your oil knocked a sensor, cap, or hose loose. If the job was done right and you don’t see any loose connections, it could simply be an issue of resetting the oil sensor or waiting for the pressure to equalize.

Section 1 of 4:

Potential Causes & Fixes of a Check Engine Light after an Oil Change

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    If air is getting into your oil lines, it’s getting into your engine. That air can throw off the air + fuel + spark formula your engine requires to combust properly. You have to open the oil cap to perform an oil change, so this is a likely explanation if the oil change was done quickly and sloppily. [1]
    • What’s the fix? Check your oil dipstick to confirm that it’s fully seated in the valve stem and then take the oil cap off and retighten it to ensure there’s no air gap.
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    Different engines require different grades of oil. Look on the oil cap to see what kind of oil your vehicle needs (5w-40, 0w-35, etc.). If the person who changed the oil used the wrong type, it could trigger the check engine light to pop on. [2]
    • What’s the fix? There’s no real way to test the oil type, so if you’re confident this might be the problem, perform another oil change and ensure you use the right oil type this time.
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    When you perform an oil change, the oil is drained and then refilled. It takes time for the oil sensors and gauges to register the new pressure level, so your vehicle may think the oil pressure is low after a change. Alternatively, if the person performing the oil change didn’t add enough oil, the pressure could genuinely be low. Both scenarios might trigger a check engine light. [3]
    • See a puddle underneath your car or white smoke coming up from your engine bay? If so, you have an oil leak. See a mechanic to have the oil leak patched.
    • If you accidentally added too much oil pressure , the check engine light won’t come on but the oil pressure light will.
    • What’s the fix? Turn the vehicle on and let it run for a few minutes before shutting the engine off. Let the engine cool and then check the oil levels with the dipstick . If the oil isn’t low, just reset your check engine light with an OBD-2 scanner. If it is low, top the oil off.
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    If the person who performed the oil change was reckless, they could have accidentally bumped into a sensor and disconnected it. A nudged vacuum hose has also been known to come loose, which can cause a check engine light to pop on. [4]
    • What’s the fix? If you’re semi-handy, pop the hood and inspect the connections leading into and out of the engine. Reconnect any obviously loose terminals or reinsert the vacuum hose as needed. If you don’t know your way around an engine bay, have a mechanic take a look.
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    This will normally trigger the oil pressure light, not the check engine light, but there’s always a fringe chance failure to reset the oil sensor triggers a check engine light. Luckily, the fix here is normally a breeze. [5]
    • What’s the fix? Turn the key to the “on” position without starting the vehicle. Then, press the gas pedal slowly 3 times in a row within 5-10 seconds to reset the oil pressure sensor. If that doesn’t work, look on your dashboard for a “reset” stick and press it down until the check engine light blinks and goes away. If neither procedure works, refer to your vehicle’s manual for help.
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    If whoever changed your oil also checked/refilled your gas tank, they may have left the gas cap loose. If they did, air may have found its way into your fuel lines, which can throw off the engine’s fuel, spark, and air ratio. That will definitely trigger a check engine light. [6]
    • What’s the fix? Go to your fuel tank and inspect the cap. Remove it and reinstall it to ensure you don’t have any air coming into your fuel tank.
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Section 2 of 4:

What does the check engine light mean?

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    The check engine light indicates that your vehicle’s onboard diagnostic system has detected an error with your engine’s combustion, emissions, fuel, or exhaust systems. This dash light indicates there’s a maintenance issue that must be addressed soon.
    • If you have an OBD-2 scanner , plug it into the port underneath your steering wheel and click the scan button. The OBD-2 device will tell you what’s causing the error.
    • A flashing check engine light indicates a serious problem that must be addressed immediately. You cannot continue to drive with a flashing check engine light. A solid check engine light typically reflects a less serious problem.
Section 3 of 4:

Why Check Engine Lights Typically Appear

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    If this is the case, you’ll need to address the underlying issue based on whatever is causing it. Potential explanations include:
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Section 4 of 4:

Should I go back to the oil change shop if they screwed up?

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    If one of those quick oil change spots messed up your vehicle after changing the oil, don’t rely on them to do the repair. Instead, see a qualified and trustworthy mechanic and then take the bill back to the oil change spot. If they give you a hard time about it, speak to the manager and explain you’ll take them to small claims court if they don’t make their mistake right. They should pay your tab. [7]
    • Unfortunately, a lot of the kids who work at those quick oil change spots aren’t very well trained. They know their way around a drip pan and dipstick, but that’s about it. It’s not rare for those shops to cause additional problems—even if it’s not intentional.

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      References

      1. ↑ https://turning-wrenches.com/audi-experts-in-louisville-to-fix-a-loose-oil-cap-and-reset-your-warning-lights/
      2. ↑ https://www.whocanfixmycar.com/advice/what-happens-if-you-use-the-wrong-engine-oil
      3. ↑ https://carfromjapan.com/article/car-maintenance/reasons-oil-pressure-light-oil-change/
      4. ↑ https://www.aeroautorepairsandiego.com/four-signs-youve-got-a-leaking-vacuum-hose-in-your-engine/
      5. ↑ https://poweroilcenter.com/blogs/resources/oil-pressure-sensor-guide
      6. ↑ https://motorad.com/3-hazards-of-using-an-ill-fitting-gas-cap/
      7. ↑ https://www.khou.com/article/money/consumer/what-if-an-oil-change-damages-your-car-rather-than-helps-it-who-pays/285-256c3cf0-9f7c-42e2-8c91-c5773861c5f9

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