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Engine Check Light Intermittent - turns off after filling tank, back on around half tank

I have 140K miles on Odyssey. Engine check light has acting … I fill the tank and it goes off. About half tank, it come back on. Sometime it will again go off before I fill it. I have changed fuel cap. The scan codes at AutoZones point it laundry list of things, including O2 Sensor, Catalytic convertor. However since check engine light is intermittent, I am not sure if I should start changing sensors. Advice?

If you’re one of those people who like to top off the fuel tank, you need to break that habit, especially if you own a newer Honda. When the gas pump shuts off automatically, the tank is as full as it needs to be. To keep gasoline fumes out of the atmosphere, modern United States cars are required to trap the fumes and recycle them into the engine to be burned. Overfilling the tank can spill fuel into into tiny vacuum lines and filters, which in turn can clog emission devices (like the “evap canister”. Soaking these devices in gasoline will cause the “check engine” light to come on. Replacing the damaged parts could be costly, but the time spent diagnosing the problem could be even costlier.

I have never topped off. Once the gas pump shuts off, i remove the pump.

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what is 02 code? p0134 or such?

I can only think of a sticking purge valve. Should you have problems starting the car in the future , that’s the first thing I would look at.

Edit: Make sure the seals around the filler cap and neck are clean and you replaced it with the proper cap.

Exactly what WERE the codes?

Thanks. I am going to check on that and let this group know.

Codes were: P0154, P0420. Auto zone was saying that they are just likely and that if one of them is bad, then Check Engine light will be more permanent (not intermittent)… not sure if that is true, but wanted to state.

Please go and pay a reputable shop to run diagnostics on it before you start throwing parts at it. p0420 could be a few different things. I had a p0420 for a month or so and every mechanic swore that the catalytic converter and both 02 sensors were bad. I didn’t buy it cause the car showed no other symptoms. I replaced the downstream 02 and it fixed it.

Why did you keep going to disreputable shops?

;-]

Does this happen every time?

I wonder, if this is an intermittent occurrence it might be pure coincident and there is a problem with the O2 sensor. Yours has a heating element, I believe, and I can imagine a dying heating element could cause infrequent failures.

Yes, it is every time I fill gas tank, the check engine light goes away. I agree, AutoZones codes are too basic, so may be it is time to pay for diagnosis :).

Unfortunately good shops are hard to come by around my neck of the woods. lol
At the time I didn’t have the time to fool with it myself.

At 140 k miles it wouldn’t be that unusual to be needing a new cat and/or o2 sensors. The link with the gas tank fill timing is puzzling though. That wouldn’t normally be involved with the cat or the o2 sensors. I think what I’d do if I had the same problem and didn’t have time to spend looking myself, and not wanting to go to a shop either, I’d replace the fuel cap and see if that has any effect. Relatively cheap, and easy enough to do. There’s a couple of valves in the fuel cap and either could be stuck open or closed or leaking. Normally that would set an evap code rather than what you are getting, but not always. Next up after that would be the o2 sensors, the cat, and the innards of the evap system. Experienced shops have methods to check the cat and o2 sensors, at least for obvious problems. Likewise for the evap system.

Did you ever figure out what the problem was? I’m having the same issue with my Nissan Altima - check engine light goes off not long after I fill up and the code is P0420.

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The same problem here with my 2011 audi Q5.

Same problem, 99 Lexus. I think it is in the evap can (or related Fuel tank vapor monitoring system.)
Not worried, but it is something I need to pinpoint before Smog Check in a year.

I have a similar problem. Chevy Camaro 2015 70k miles. I fill the tank up and by the second or third time I turn on the car the check engine light disappears. By the time the gas tank goes down to about 3/4 tank then it the check engine light comes back on. I took it to arnie bauer’s GMC and the first day I brought it in the code was o2 sensor running lean. Then by the following day the check engine light didn’t come back on they said they couldn’t figure out the problem. Next step is to take it to Phillips Chevy and see what they could figure out. I had been keeping the has tank low the last couple of weeks, I don’t know if that’ll have a part to do with the check engine light. When the gas tank was under a 1/4 tank it’ll start idling roughly at a stop sign or sometimes turnoff. Any idea as to what the problem could be? Since gas tank been full no more rough idling nor has it turned off but check engine light comes back on after gas tank goes down to 3/4 tank

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I have same problem with my chev aveo 2013. Your cam shaft sensor is the problem.

Same problem here. I have a 1999 Honda Accord with 95,000 miles. The check engine light goes off shortly after filling the tank and comes on about 3/4 full every time. I changed the first O2 sensor and spark plugs (it was time) with no change. Not sure what to do next. Maybe I will keep it full and see if it stays off for a period of time.