My check engine light is on and I DON’T CARE!!!


More often than not we get 2 responses when asking a customer if they would like us to diagnose their warning light problem:

#1:  “Oh yea, I know what that is, it’s been on for about a year and the guys down at the auto parts store put their cracker box on it and told me it just needs a sensor.  I’m not worried about it. Seems to run ok.”

#2: “How much does it cost to diagnose?  OMG!!  I think I’ll just not worry about it right now.”

It seems to be rare that a customer will willingly come in on their own and have their check engine light diagnosed if there are no symptoms associated with it.  Don’t get me wrong, we diagnose and repair lots of check engine lights that don’t produce symptoms, but we get a lot more that do have symptoms such as rough running engine, low fuel mileage, noises, etc.  And I get that, it’s hard to spend money to do nothing other than turn off an annoying light bulb..  right?!

WRONG!  Lets dive into just exactly what it means when the check engine light comes on.  When that little bugger lights up your life, it means that the computer has saw something happen outside of what it expected to see.  The computer is programmed to more or less know what to expect under certain conditions and when that either doesn’t happen or happens in a way that is implausible, then it will log what it saw happen that it didn’t like in the form of a trouble code and turn on the check engine light to alert the driver that something is amiss.

Computers are very good at compensating.  The computer’s goal in life believe it or not is NOT to keep the car running smooth.  Smooth and proper operation is simply a byproduct of its real job which is to keep harmful emissions within limits set by good old Uncle Sam.  When something goes wrong, it’s the computer’s job to try to compensate for it to keep emissions as low as possible and often masking any symptoms that might have been present had there been no compensation. The government isn’t gonna put the smack down on a car manufacturer if it doesn’t make all the power it possibly can but you can bet law suits all around if the emissions aren’t within check (think Volkswagen)!  Modern engines could make TONS more power if they weren’t forced to meet the strict emissions requirement the EPA has set forth and its a good thing.  Have you ever been driving behind an older vehicle and smell exhaust fumes?  I bet you have.  But you won’t if you are behind a vehicle produced within the last 15-20 years thanks to strict emissions requirements as long as nothing’s wrong that is.

So if the computer compensates for the problem and I don’t feel anything different in the way the car runs, why worry about it?  Glad you asked!  There are several reasons.

Scenario #1: Check engine light is on.  No symptoms.  The problem the computer saw was an incorrect up stream oxygen sensor signal.  Upstream oxygen sensors are responsible for telling the computer whether or not it’s getting the amount of fuel it’s putting through the fuel injectors right.  The computer has complete control over the amount of fuel that it injects into the engine through the fuel injectors and it decides how much by looking at several other sensors and then coming to a conclusion based on those sensors.  The Oxygen sensor tells the computer if it got it right.  Usually it does, the check engine light is off and everyone is happy.

But what if it’s not getting it right?  Lets say we have developed a vacuum leak.  The O2 sensor says HEY!!! WHAT IS GOING ON!!  NOT ENOUGH FUEL FOR THE AMOUNT OF AIR COMING THROUGH!!!  Computer says, well look Mr. O2… the air flow sensor says this is how much air I’m getting, so this is how much fuel I’m putting in.  O2 says sorry bud, but it’s not right.  Computer says ok fine and makes the compensation to keep the O2 sensor happy and the driver is none the wiser except for the check engine light that has recently illuminated.  A vacuum or air leak is air that is getting into the engine that the airflow sensor can’t sense.  All air entering the engine must go through this sensor.  If it gets in elsewhere, we have a problem.  So now the computer is having to add more fuel than it normally would to compensate for this extra air entering the engine somewhere.  The computer is no longer in complete control of the fuel system.  Reduced fuel mileage, higher emissions, and undue stress on the engine can and likely will result if this problem is left unchecked.  There is also a limit to which the computer can compensate and if the air leak becomes large enough, the engine will begin to run bad and/or not at all.  Why not get this fixed for less money BEFORE you are stranded?  Makes sense to me!

Scenerio #2:  This time we will use a different warning light, the Antilock Brake System (ABS) light.  The ABS system is designed to prevent the wheels from locking up during hard braking.  When the wheels are locked up and the car is still moving, you have absolutely NO control over where that vehicle goes.  If we can prevent the wheels from locking up, then at least you can still maintain some control over the vehicle and possibly avoid hitting something.  ABS does not really help you stop sooner.  Just with more control.  WITH THAT SAID…  ABS light is on.  Brakes still work, car stops when the brake pedal is pressed.  It’s just an ABS light, why worry about it?  It’s not like I’ll be left stranded over an ABS light.  It has nothing to do with the engine.  All true statements.

In this situation the reason the ABS light is on is that the ABS computer is not receiving a signal from the left front wheel speed sensor.  The wheel speed sensors are critical for the proper and SAFE operation of the ABS system.  I mean, the system needs to know if a wheel is locking up and if the wheel speed sensor isn’t working, how’s it gonna know that?  It won’t.  So at that point the ABS system is largely disabled as the computer has determined that it no longer can accurately determine when the wheels lock up so rather than activate the ABS when it’s not needed (which could be potentially catastrophic) it just disables the entire system and turns on the warning light to alert the driver that there is a problem.

Ok, big deal.  I can still stop..  Yea you can but your driving along one day and your neighbor’s dog runs out in front of you.  You slam on the brakes and turn the wheel hard to miss him, but your ABS isn’t working and the front wheels lock up.  Even though you have the steering wheel cranked as far as it will go, the wheels are just sliding so it doesn’t matter which way you WANT to go, the car plows on straight ahead and… well…  I think you know the rest.  Had the ABS been working, the wheels wouldn’t have locked up therefore the car would respond to your request for a direction change and likely the collision could have been avoidable.  Thankfully it was a dog and not a person.  Would the repair have been worth it?  Yep.

I’m not trying to scare anyone here.  But as cars get more and more complicated and people become more and more unaware of what is going on behind the scenes in the modern vehicle, we all have sort of an obligation to keep not only ourselves but those around us safe by not polluting the air we all have to breathe and by not running over our neighbors dog (or worse).  Accidents happen.  That’s a given. By keeping your vehicle repaired and well maintained we can drastically reduce the amount and severity of vehicle related safety concerns not to mention save tons of money in the long run!

Call us or visit us online today and schedule that warning light diagnostic and repair.  Your kid’s and grandkid’s lungs and your neighbor’s dog will thank you for it!