Check Engine Question

[jmc67]

Hello,

I have a 2005 Elantra GLS - 4dr. Sometime in June the check engine light came on (1st time). Not sure why it came on but the assumption was that the gas cap was not tighten correctly since that same day the tank was filled. I went ahead and reset by removing by disconnecting the battery. No light came on until just yesterday (aug 19). This time, the tank was filled a few days prior.
So my question is, if there were a major problem, wouldn't the light come on much sooner? The car is driven 50 miles (highway then local streets) each day - 2 days out of a week.

[PlanetDude]

Check engine lights are a finicky thing. It`s very possible these two occurances are not related at all.

Your on-board computer monitors the input from many sensors, several times a second. Anytime the computer receives an out-of-spec signal from a sensor, it will set a check engine light code, which turns on the light.

I have had several instances where I get a CEL, I plug in my OBDII scanner, check the code, clear it, and it is never seen again. It could be any number of small factors.
I am NOT saying this is what is happening in your case, merely a possibility.

Rule of thumb is if it CEL is not flashing, you can have it checked when your dealer or garage can accomodate. If you don`t have your own scanner, I recommend having it checked. Even if it is a "nothing wrong - one time off" code, it`s still good to troubleshoot that - you don`t want to have a larger problem developing if you can nip it in the butt.

This is just my two cents. If you have any other information (even find out what the code is) post on back, I may be able to add more.

Ryan

[jmc67]

What reader do you have? I plan on purchasing the Actron OBD II code reader - Part Number: CP9125 from autozone tomorrow so that I can pull the code. Is this a good reader?

[PlanetDude]

I have an Innova 3100a..... never hand any trouble with it. It only does OBD2, which is all I need it to do.

I didn`t do a lot of research, I just knew it was the one my stepdad had researched heavily and bought for himself.

You`ll find if you are a DIY`er with a couple of cars, a few code reads will pay for the cost of the tool. I`ve already saved more than what I paid.

Ryan

[jmc67]

Ok, I got one of those OBDII Code reader and the code is P0455 (EVAP Emission Control System Leak (Large). Gas cap maybe? I say gas cap only because the first time the light cam on, I reset and then two months later the light came on again. Keep in mind that the car is driven 50 miles each way during the week. If this were an issue, won't the light come on much sooner? Can experts elaborate on this? I'm no expert myself.

[PlanetDude]

Gas cap usually triggers a SMALL evap code.... (again, I am no expert...) I would suggest checking all the evap hoses near the back, by the gas tank..... as well, there is a small black charcoal canister like box, on my wife`s 99 Sonata, it was behind the rear wheel, inside the bumper cover.... check the condition of the hoses there.

I am no expert on EVAP, but if you find any leaking or rotten hoses, that may be your start. I also suggest clearing the code and taking the car for a drive again. See if it even relights the CEL.

ON the Sonata, I got an EGR code one night back in 2007. Cleared it the next morning, never seen it since. (Not saying you will have similar luck, but now that you have a scanner you can clear and monitor the situation).

Post back with any updates..... I don`t know how much I can help you, but I will certainly try.

Ryan

[jmc67]

Hi,

You have been helpful. I'm not sure if I should clear the code only because my wife decided to take it in for a check at the dealer this Tues. I know for a fact that if I clear the code, it will most likely not come on again for another two months as it initially did. My gut feeling is that it could be the cap but my wife still want a mechanic to check it. Would you clear the code, cancel the appointment and see what happens? I will need to convince my second half. Hopefully she'll agree.

[PlanetDude]

My 99 Sonata lit a P0455 on Sunday night, cleared it, no sign of any reoccurance.

Explain to your other half that since it went out and did not return, it was likely a sensor that threw a wonky signal, once, and that it shouldn`t return. If you clear it and the light comes back immediately, or very shortly (within say 24 hours) then is the time to take it to the mechanic, because it is indicating a problem.

Since check engine lights are SO precise (your car is scanned a few times each second, at least) if it gets ONE signal out of spec, it`ll trigger that light. Cold night, EGR is slow to move? CEL. Hot night, humid in the vacuum line? CEL. There`s at least $120 in a shop`s bank account.

If you clear it and it stays away, write it off as a one-timer. Keep a record, so if you happen to notice a trend (it gets below 50, you get X code everytime) you can act accordingly. If you know car basics, these new on-board computers aren`t so hard to understand.

Hope I`ve helped (with the car and the better half).
Ryan

(PS - if the light has stayed out and you`re confident, cancel that appt.)

[jmc67]

We went ahead and did not cancel the appointment. Service center did not find anything wrong and blamed it on the gas cap not being tightened correctly. They also reset the code. Luckily, they did not charge me for anything so I am happy about that. So far the light has not turned back on.

[jsinton]

Originally Posted by jmc67

We went ahead and did not cancel the appointment. Service center did not find anything wrong and blamed it on the gas cap not being tightened correctly. They also reset the code. Luckily, they did not charge me for anything so I am happy about that. So far the light has not turned back on.

It's probably correct, P0455 is "gross leak". If it was something other than gas cap, you would have known it. EVAP codes take a while to light, however. Run a tank of gas, then you'll know.

[jmc67]

Filled the tank 5 days ago and the light has not come on.