2003 toyota corolla-check engine light on. 105,000 miles. checked gas cap. any other ideas?

Answer 1

could be the oxygen-sensor bad

Answer 2

I love people who yell O2 Sensor every time someone says they have a check engine light on. There are something like 1,700 different fault codes that can trigger a check engine light. The number of those that can indicate a failure of the O2 Sensor(s) can probably be counted on one hand with digits left over.

Ridiculous.

Let's start with the basics. The Powertrain Control Module in your vehicle is a computer that both runs and monitors all the functions in your engine For emissions compliance purposes when the PCM finds a problem with some facet of the engines operation that might effect emissions it triggers a fault code specific to the nature of the problem detected. When this fault code is registered and stored in the PCM the check engine light is illuminated. If it is a Type 1 or "hard" code, the light remains illuminated until the code is manually removed by using a scan tool or code reader designed for that purpose which plugs into the PCM. This same tool allows you to read what the code is.

Let's use an example of a very common code; A misfiring cylinder would trigger a P0300 Random Cylinder Misfire code, which you would then see on the tools display. Possibly, this same problem might trigger other codes too. Let's throw in a P0301 - Misfire in Cylinder #1, just for fun.

So you've hooked up a scanner or code reader and found the code(s). Now what do you do with this information? Does just knowing the code tell you what to fix?

Usually not!

The code just tells you where to start looking because what the fault code gives you is the symptom, not the cure.

Example; If I were to post a question here saying I had a P0300 and P0301 code for a misfire I bet I would get a dozen responses saying to replace the spark plugs. However, spark plugs are only 1 of many things that could trigger this particular code. If there is an individual ignition coil for each cylinder it might be a coil failure. Barring that, it could be a faulty ignition wire or spark plug tube (for coil-on-plug setups). On dual-overhead cam engines oil could be leaking from the valve cover O-ring that seals the spark plug hole in that cylinder. Or the fuel injector for that cylinder could be malfunctioning. But even then is it a bad injector, a clogged injector or a problem in the PCM itself which is causing the injector to not fire when it is supposed to? Perhaps a mouse chewed through the wiring harness for that injector (seen it more than once)? There are other causes too but you get the idea.

So, to find out why your check engine light is on you need to start by having the code pulled. This can be done at an auto parts store - often at no charge - but these guys are not equipped, trained or qualified to do the kind of diagnostics required to properly identify most problems. Even to find a parts guy (or gal) with a remotely useful knowledge of parts is a rare thing indeed. These folks use cheap "Code Readers" that cost just a few hundred dollars and that only read what the code is and don't offer any troubleshooting tips or diagnostic aids. Often they will do things like pull a misfire code and sell you some spark plugs that don't fix the problem. Or sell you an EGR valve because they pulled an EGR related code but that won't fix the problem either because a the EGR issue is the symptom, not the problem.

Or you could take it to a mechanic who has a Diagnostic Scanner that costs several thousand (up to $10k for some units) plus hundreds of dollars/year to update which can pull up not just generic codes like the cheaper readers but also vehicle specific codes. It can view everything that is happening in the engine in real time, see a snapshot of exactly what the engine was doing the instant the code was stored, has troubleshooting tips and specs for all of the related sensors, electrical components etc. He's not gonna do this for free. He's gonna want $80-150 for the pleasure but then, your chances of success are much higher. The problem may be a simple one, it may not, but its the expertise and the equipment your paying for. Do whatever you want.

Or you could ignore it and put black tape over the light. Whatever works.

Answer 3

Oxygen Sensor...you may be able to fix it yourself--check a Haynes manual that you can pick up at the auto parts store. Or you could just take it to the mechanic. It seems every check engine light is a result of a failed sensor.

Answer 4

I know a single missfire will set a light off. When is the last time you had a tune up? New plugs, wires, o2 sensors?

Answer 5

contact a toyota dealer usually what happens after 100,000 miles the light comes on atomatically and you need to reset a switch or some damn thing :)

Answer 6

in order to find out with some certainty you need to hook - up a or some kind of vehicle scanner.this will lead you in the right direction.