Celica Forums General Discussion General Service Engine Soon light came on

HI all. I know there could be like 300 things that may have caused the engine light to come on but I checked all the fluids and no other lights came on. I was just driving down the highway this morning and the light came on for no reason. The car is running fine no weird sounds or knocks or anything that I can tell. I was wondering if there is like a sensor or something in the oil or maybe in the antifreeze or something that may have kicked it on. I tried shutting the car off and then popping the clutch while I was going down the highway to see if it would kill the light but it still stayed on. Any thoughts. I know really rather vauge but just seeing if anyone else may have had this problem. Thanks in advance all.

Your catalytic converter could have failed. If it does, the O2 sensor after the cat would of triggered the check engine light.

You should go down to like an Autozone, Pep Boys, Kragen or any automotive care store and see if they can read your OBD II to see which code it says caused the check engine light.

For your informational use only: Make sure car is off, open hood, carefully remove the NEGATIVE terminal of the battery ONLY. Do not remove the positive terminal. Leave it disconnected for 10 minutes and it will reset the ECU. Connect it back and your CEL should go away. In some cases, it might come back on.

Could be something as small as the gas cap not tight enough...

exactly have you filled up on gass lately?

If it's not the gas thing or one of your O2 sensors, check your MAF sensor and maybe clean it. If all else fails, take it to a dealer and they will read the code for you to tell you what's triggering it.

Before you go anywhere disconnect the negative terminal of the battery for at least 10 minutes to reset the ECU like Steven said.

How many miles do you have on your car? I know mine came on when it was time for my 30,000 mile check-up!!

You engine could have miss fired, all it takes is one for the CEL to come on. I know a few people who have gotten a CEL for that, you wouldn't notice it if you were driving down the highway and your car would otherwise run fine.

before you reset it take it to advance auto they will scann it for free and then you can post te code and we can tell you whats wrong

That was the reason my came on for a little while. On and off, until I got gas.

WOW!!! A lot of replies and I really appreciate it. I know this is a little down on the list in this forum now but troublecode is OBDII (alpha) P Code trouble shooting P0420 and it has something to the effect that the catalyst system efficiency is below threshold. I will go ahead and disconnect the neg term and see if that helps. I really appreciate all of the help guys I was really starting to freak out and all. I have only had my car for a year and I thought something major might have gone wrong. Thanks for all of the help.

Hey Bartiks, I just looked the P0420 code up in my repair manual and this is what it said.

DETECTION ITEM: Catalyst System Efficiency Below Threshold (Bank 1)

TROUBLE AREA: Gas leakage on exhaust system
Open or short in heated oxygen sensor circuit
Heated oxygen sensor
Three-way catalytic converter


If re-setting your ECU doesn't help, then those are the cause of the problem. If you are still under warranty, I would just take your car in if I were you because if it detected a problem with the oxygen sensor or catalytic converter, it could cost you a lot to replace if it failes later when you have no warranty left.


btw, good call Steven, sounds like you were right.