Hi, I’ve used your services in the past. However I had a ...

Hi, I’ve used your services in the past. However I had a check engine light come on recently. I did use 89 instead of 93 in an 2011 Mercedes [c300](/topics-c300/) Mechanic's Assistant: Does the light stay on, or does it bl...

Hi, I’ve used your services in the past. However I had a check engine light come on recently. I did use 89 instead of 93 in an 2011 Mercedes [c300](/topics-c300/) Mechanic's Assistant: Does the light stay on, or does it blink? It blinked a couple times when I started engine but it has been a steady on. Some smoke came out the first time but no longer Mechanic's Assistant: Are you fixing your C300 yourself? What have you tried so far? I haven’t tried filling it up yet with good quality 93 gas. I’m not sure if I should try an octane cleaner. It’s a Mercedes so it’s fickle Mechanic's Assistant: Anything else you want the Mechanic to know before I connect you? That would be all

Automotive Expert
Welcome to JustAnswer. Thank you for contacting us for assistance with your vehicle. I'm Pete. I will be happy to assist you with your question. May I ask to whom I have the pleasure of speaking with today?

Automotive Expert
Hello George. Nice to hear from you today! I'm sorry to hear you are having this problem. I know this can be frustrating. Wa anything else done to your vehicle recently that may have caused this issue to occur at all?

Nothing, I really haven't been using it as much in the last several months as I work from home. It had a B service, oil change, filters etc. in July 27 2020
Automotive Expert
Thank you for your reply and that information as this does help me better understand the situation. Please give me one moment to type out some info for you. I’ll be right back!

Automotive Expert
Thank you for holding George! The blinking check engine light that occurred at first is to let you know that the engine computer detected an engine misfire. The light went solid as soon as the engine misfire stopped occurring. I suspect that one of the [spark plugs](/topics-spark-plug-mercedes/) didn't fire off properly right away or an injector issue due to lack of use that cleared itself up. This was common when the engine sits for a period of time without use in some cases. In order to determine if you need to just have the codes cleared out or if there is a fault with an engine component that has to be repaired what needs to be done is to have a fully compatible scan tool plugged into your vehicle's data port that can read all of the computers in your vehicle to see if any fault codes are stored with this issue. Once this has been done, any codes that come up can then be diagnosed to help pinpoint and repair this issue. This will require the use of a high-end scan tool that can read all of your vehicle's computers. If you do not have a scan tool to check the fault codes yourself a shop or dealer can check the fault codes as well as diagnose the issue for about a 1-hour labor charge ( around $100 ). The cost to repair the problem varies as it depends on which component has failed that requires repair or replacement. I suspect all that is needed is to have the codes cleared out to resolve this issue. The 89 octane fuel wouldn't have caused this issue. I do recommend the high octane fuel for your vehicle for optimal performance and for engine stability as Mercedes does request you use the highest octane available at the pump.

Thank you, \*\*\*\*\* \*\*\*\*\* think I could try filling up better gas and see if the light goes off or just bring it in?Don't know if I should drive it
Automotive Expert
Your welcome. I do recommend to top off the tank with the correct or higher octane fuel when you can. As long as the engine is running well and the vehicle is driving and braking well with no continuous smoke from the [exhaust](/topics-exhaust-mercedes/) you should be o.k. to drive it for now. I do recommend having the codes checked though as soon as you can.

Ok will do... what about adding a fuel cleaner as well to the tank of gas? A good idea or not ?
Automotive Expert
I don't recommend adding any cleaner to the tank unless an issue is found with the fuel injectors operating incorrectly. In some cases, a cleaner can harm fuel pumps and injectors when it isn't needed.

That's what I figured, thank you for your response
Automotive Expert
Your welcome! Glad I could be of some help! I hope everything works out well for you! If there are any additional questions on this issue that should arise, please feel free to reply and ask! Thank you for choosing Just Answer for your questions. Have a great day!

Same to you
Automotive Expert

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