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What Does Check Engine Light Mean

Written by maryp posted on Wednesday, May 9th, 2012

3.00 avg. rating (70% score) - 1 vote

Example of engine light in BMW 3-seriesHelp! “Check Engine Light” was on, but I drove for a while and now it’s off. What’s with that?

Your MIL light, (Check Engine Light, also called Service Engine Soon light in some BMW years/models), turns on when a fault, (Diagnostic Trouble Code aka DTC) is detected related to emissions and your OBDII(Onboard Diagnostics, second version). It is about clean air.

There are probably 100 different “things” that can trigger faultsand then cause your Check Engine Light to illuminate. Some are serious, others are not too serious.

For example; a loose gas cap. You just filled up, but neglected to tighten the cap properly. Now your MIL light is on. Just because you tighten the cap, do not expect that light to turn off immediately. The car must go through several specific drive cycles before the light goes off. Even the gas cap is part of the vehicles “evaporative emission system”. (That’s why it is being tested during your CA smog test).

Suppose, the light comes back onafter a day or two of regular driving? Now, it is probably a completely different fault, (unless you did not tighten the cap again), related to emissions.

The only way to know what is going on, is to get your BMW, MINI, Mercedes or other car checked out. The codes are pulled, the problem traced, verified, then repair is made. Your shop should know what the parameters are for the various drive cycles, and also be able to perform those on a dynonometer, so they know, (and you know) that the “fix” is really the “fix”. So, after a battery replacement, reprogramming or code clearing, after the drive cycles are completed, the “monitors” re-set. Then your car’s system begins checking all of those emission related items, again…..

Remember that if your check engine light comes on and you are told that you have a PO420 code, or commonly called at “cat code”, you may not need the catalytic converter replaced. Only a California Smog Test and Repair station, (such as The Driving Machine, Inc) is legally allowed to repair emission systems. A “cat code” can be caused by a defective O2 sensor, an exhaust leak or fuel mixture being out of spec and a few other situations. Any of those can cause the Check Engine Light to come on and flag one of those PO420 codes. But, unless there is a proper diagnosis, you could be spending a lot of money on a catalytic converter and not really fixing the real problem.

If your Check Engine Light is on and you need to check it out, make an appointment online. We will tell you why it is on and what you could do to get the problem fixed.

3.00 avg. rating (70% score) - 1 vote

One response to “What Does Check Engine Light Mean”

  1. Longino Mucheusi says:

    My check engine is on, they tell it may be sludge in the engine therefore I need to replace engine. Am doubting as the engine is running perfectly well for the last 6 months, with the light on.

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