Quote:
Originally Posted by BlackKnight  It's my understanding all after market headers generate a CEL. They remove one of the Cats and make the exhaust flow much more efficient which causes the computer to generate errors. CEL eliminators are not "bad" for your car, they just pull the sensor back from the access port a bit so the computer senses the same restriction on air flow as the normal manifold. the CEL eliminates only the error for the header and should still generate errors for other issues as normal. |
While you are correct in attributing the CEL to the elimination of the Cat, it is not the increased air flow that is the problem. The secondary O2 sensor monitors the efficiency of the Cat by measuring the level of emissions present in the exhaust gases. When the cat is removed, the emission levels increase and the ECU triggers a CEL since it thinks the Cat is no longer doing its job (which it's not, it's not there!).
What the O2 simulators do is send a constant signal mimicking what the ECU would expect to see if the Cat was operating correctly. The CEL eliminators that space out the O2 sensor from the exhaust flow simply reduce the amount of gases seen by the O2 sensor and thus the level of emissions seen.
Removing a Cat is against FEDERAL emissions standards, which would make it illegal outside of California as well. The difference is that most states don't perform the types of emissions tests that would ever check for the presence of the cat.
