Mullet

last night i filled my car up and 5 minutes down the road my check engine light came on......... any ideas on why this would of happened? i changed my exhaust the other day , would that have anything to do with it? thanks in advance guys, Will

ballerx

Hey dude, just take off either the positive or negative on ur batter for like 3 min, it will rest ur ecu and u be all good, usually the light comes up after there is a change in exhust system or something, check your o2 sensor also cuz that can set it off also. Mine came on right after i put my intake on, i reset it and hasnt been on since then.

Let me know if u need anyting else.

flipside909

You possibly got an O2 sensor faulting perhaps from not installing it properly or failing. Reset your ecu by taking out the EFI fuse for a minute and reinstall. This way you don't lose the memory from your radio or your memory seats if so equipped .

UncleNick

Here is the problem. The light is on for an evaporative pugre code(gas cap not tight enough.....serious). These OBD2+ cars will throw a check engine light if the gas cap is not tight enough. Fords and Toyota are notorious for this. Make sure gas cap "clicks" after fueling car, disconnect the battery for 10 min, light will be gone unless you need a new gas cap.

Mullet

ok heres the deal.... i went and had it checked out and they said that the o2 sensor is bad.... what would of cause that and will it go bad again if i replace it?? thanks guys

Mullet

its the o2 sensor at the mainfold...

flipside909

Bad O2 sensor? Probably a faulty sensor unless your setup is causing your O2 sensors to go bad. Your O2 sensor should be covered under the federal emissions warranty.

flipside909

That's only ONE possible cause. But since he was talking about changing his exhaust and having the CEL come on...then ITS NOT the gas cap. And for Toyotas, you can remove the EFI fuse to reset the ECU instead of unplugging the battery.

Mullet

have any of u guys changed your exhaust and experienced the CEL coming on??? just wondering

flipside909

Yes. My fix...was to remove and reinstall the sensor.

Mullet

thanks ill try that and let u know how it went

r0llm0del

i had the same problem except my car is still stock. i took it into a lexus dealership to see what it was and they told me its the oxygen sensor as well. one of the mechanics just did a quick diagnostic with some machine hooked up under the steering wheel, and he said it wus a code 161 or some ****. anyways hes tellin me with parts n labor, its gonna run me 400 bucks. have any of u guys heard of something as outrageous as that. i think its bullshyt to tell the truth. please gimme lots of feedback. cus i really dont think and oxygen sensor would run the bill up dat much.

flipside909

Unfortunately, the labor is what makes the price go up. The sensor itself is under 100 bucks. I bet the same procedure at a Toyota service dept will cost a fraction of the cost. 400 is definitely outrageous. Take it to an independent...or if you really have to, a Toyota service dept.

mmarshall

Flip is correct...the first thing to always check is for a loose gas cap. The vaccum seal on the cap is critical for the evaporative-control sensor. The slightest air leak will trigger it. Now, for a bad O2 sensor, something as simple as a bad tank of gas or dumping the wrong kind of fuel system cleaner, octane booster, etc... can mess it up by throwing the oxygen content in the exhaust gas way out of whack with unnecessary pollutants. One of the biggest problems with old O2 sensors can be just getting them out...they get so hot and the threads get so burned-on that it can be quite difficult to unscrew them, and this requires special procedures. One thing I always tell people to help keep bad fuel out of the tank is NEVER gas up at a station when you see a tanker truck refilling the underground tanks. The pressure from the big truck hoses stirs up all the crud on the bottom of the tanks and that crud (and sometimes water) and that stuff just goes right into your tank....and plugs up.the fuel filter.
I have heard technicians recommend O2 sensor replacement at 50,000 mile intervals. Seems like overkill to me and maybe an unnecesssary expense, but it couldn't hurt.

mmarshall

Flip, you mentioned that the O2 sensor may be covered under the Federal Emissions warranty. Yes, that is a good point. The O2 sensor is probably the second most important piece of emissions hardware in the whole system...right behind the catalytic converter. I got a question: just how long is that warranty......do you know? I've checked several sources and they don't seem to agree. My last post mentioned that techs sometimes recommend replacement at 50K intervals, but why do that if it is warrantied longer than that?