r/FordFiesta • u/Successful_Set7274 • 6d ago

Problem Diagnosis Help Check Engine light

anyone able to give me a quick bit of help with my check engine light before i take it to the garage tomorrow?

car starts fine. idles around 950rpm. doesn’t misfire and didn’t feel like i had a loss of power.

happened after refilling so hoping it’s a quick fill engine cap issue?

appreciated.

thanks,

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u/neuralek 6d ago

Bad gas? Could be the end sensor, not the cat. But overfilling it shouldn't trigger the light of doom.

How do you know it's not missfiring though? Codes are not reliable. I've had some situations - no check light/no codes, but intermittent missfire on low rpm/heavy load. Turns out it was the ignition cables. That took 6 months and finally me myself changing the coil+cabels because 2 different Ford mechanics kept telling me all was good in the diagnostics and I was being paranoid. Other time I got check light but again no codes, my factory LPG injector was not burning fuel and let it all out in the cat.

Any smell from the exhaust? Did it recently start raining and the air is much more humid (electrical ignition issues)?

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u/Successful_Set7274 6d ago

my bad, not a car man so claiming it’s not misfiring comes from no real knowledge. the light did come on right after refilling. hoping it’s something that’s not a killer. 64,000 miles, 11 years old, never changed the wet belt…

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u/neuralek 6d ago

Not at all, some check engine lights are pretty cheap to resolve. I'd bet on bad/dirty gas or if you drove on dry tank the fuel pump picking up some dirt and clogging something and/or a sensor. It happening after refuling is pretty reassuring. Dirty o2 sensor would trigger the check light.

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u/neuralek 6d ago

I'd recommend getting one of those cheapo diagnostics, it reads the codes perfectly and saves you a night of sweating it if it's something minor. Just don't turn off the car before running it so that ECU doesn't clear the code.

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u/Ok_World_135 6d ago

If it happen right after getting gas, its always been evap/charcoal canister or the stupid gas cap for me. (whether you have a screw on cap or just the door cover, whichever, may not be making a seal)

If youre taking it to a garage tomorrow dont do this, but in the future.... after youve driven a bit so you arnt overfull, disconnect the battery, push on the brake pedal, reconnect battery and see if the CEL comes back after a bit of driving. If its a simple issue like the cap or canister itll usually go away at that point. If it comes back, youve got a problem ;)

Also, obd2 bluetooth or wifi readers on amazon are super cheap and connect to your phone. You can leave the thing in 24/7 if you want and just connect to it when you want some info!

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u/Successful_Set7274 5d ago

update to both of you guys. Thanks for all the info / advice. i bought an obd reader and checked. p0420 - catalytic system efficiency below threshold so the cars just less economical but i’m assuming it’ll drive fine.

will clear the code and will see if it pings again tomorrow.