"Check Engine Light" e-check(Ohio) and passing the e-check

[Gary_T]

@samclem

Guess here. The computer “knows” on a 2003 whether you install a “genuine Toyota part” or an aftermarket part.

@jz78817

unlikely; the converter doesn’t have any active electronics on it. The only way the engine management would know that the converter’s not genuine is if it doesn’t work; e.g. the downstream EGO sensor doesn’t read differently enough from the upstream.

@Rick

As has been said, the converter has no electronics…This does not imply that a $200 aftermarket converter is as good as a $800 factory unit, it might not be.

@samclem

I think what happens is, if you install an aftermarket converter on a 2003 Camry, the check engine light will come back on and stay on. The computer, for whatever reason, senses it.

@Magiver

As stated above, there would be a pre and post ox sensor in relation to the converter. The only thing a computer can do is respond to the input from the sensor.

@Rick

That is because the aftermarket item is a piece of shit, not because of anything Toyota did. While I have not looked I am sure you can find an aftermarket unit that does work, and won’t light a CEL on this car.

Let me see if I can clear this up.

The computer does not directly sense a non-factory converter, as stated it monitors the oxygen sensor readings of the gases exiting the converter.

Aftermarket parts are typically reverse-engineered; a factory part is examined and a replacement part is designed to duplicate its function. While this is successful the great majority of the time, there are cases where for some reason the aftermarket part doesn’t measure up to the job. Experience in the field has shown that for some applications, even good quality aftermarket converters will end up triggering the check engine light. Presumably the factory set-up is very touchy about the readings it’s programmed to see and the aftermarket converter is just not engineered precisely enough to meet all the parameters. So for some cars, the computer will “know” there’s a non-factory part because that part doesn’t exactly duplicate the factory function as measured by the relevant sensor(s). The part may or may not be a piece of crap, but if it doesn’t keep the light off it’s still not good enough.

[Dallas_Jones]

OBD II diagnostic systems use Monitors (up to eleven) that are a set of diagnostice strategies programmed into the PCM (car’s computer) to tell the PCM when to turn on the check engine light.

Each monitor watches a separate part of the engine’s system and uses a set of conditions called Enabling Criteria. Some monitors conditions only require that the engine is on, others require a number of cold starts, engine warming to operating temperature or driving conditions such as accelerating, cruising, etc.These cycles are called ‘trip drive cycles’ and the amount of driving to satisfy the cycles for all the monitors will vary. Once the enabling criteria for all monitors have been met you have 1 OBD II Drive Cycle.

When you clear the codes the PCM will read something like ‘Monitor has not run’. This is how the testers know you have cleared the codes and your car is not ready for the emissions test.

It is possible to clear the codes, go through enough cycles to get the PCM to read ready to test, but not go through enough cycles to reset a trouble code and light the engine light. A ‘sweet spot’ where you can pass the test.

But you probably are not going to be able to know when you have reached that spot. You may have just got lucky when you previously had codes cleared and passed the test.

Most of the information above is from the manual for my handy little OBD II tester that stays in my glove compartment. I got it several years ago because the local gas station idiots kept not putting the gas cap on correctly causing an EVAP code and an engine light. No, I am not allowed to pump my own gas in Oregon.

It has come in very handy for tracking down other engine issues too. I highly recommed getting one if you are the sort of person who ever opens the hood of your car, changes plugs, or does routine maintenance. Best $100 I ever spent.