Jan
31
2010
‘Check Engine’ light
Author: TkWhen the check engine light comes on, you should always have it checked out…
But what does it mean exactly, when the engine light comes on? The main thing your engine light is telling you when it is on is that there is something wrong with the Emission output of your vehicle…
When your engine light comes on it means that something in the drive train of your vehicle (the engine, transmission or differentials) has malfunctioned to the point that it has changed the standard fuel and exhaust emission output, for the year, make and model of your vehicle.
For example, an engine miss would change the output of your emission. When the engine miss-fires (misses) it expels unburned fuel and air out the exhaust, causing more pollution.
The exhaust has oxygen sensors which monitor the amount of oxygen in the exhaust emissions, when the oxygen levels are out of parameters too long the computer in your vehicle, that receives all the information of the performance of your vehicle, turns on the ‘check engine’ light. You may never feel your vehicle run badly and still the check engine light would be on. The computer in your vehicle will also store a trouble code and it will freeze frame data of the event, making it easier for a technician to diagnose your vehicle and see what the exact problem is.
There are numerous emissions monitored that way, for example, the amount of fuel vapor that returns to your fuel tank is also monitored. That system goes through routine testing; it lightly pressurizes the vapor return hoses, piping and fuel tank. If it would leak off pressure (which means raw fuel vapor being emitted into the atmosphere) this system would notice and it would turn on the light as well.
The stored data in the computer of your vehicle, like I mentioned, makes it easier for the technician to find the cause of the problem, with the data of the computer he can pinpoint the location that gives trouble. Understand though that that when someone accesses the trouble codes in the computer of your vehicle, it may have a sensor reference with it that says something like: ‘O2 sensor lean’ or ‘rich’. This does not necessarily mean the sensor itself is lean, rich or bad in any way, in this case the sensor might tell us the oxygen levels are way off, but this is where the technician checks under the hood…
At one point I had a customer call my garage one day frustrated because he had four new oxygen sensors and his check engine light kept coming back on. The part store had sold him new oxygen sensors because their ‘trouble code reader’ said “‘Oxygen sensor too lean” and they thought the sensor were bad… However when he pulled up to my garage I could hear what sounded like a large vacuum leak on his engine (sucking air in where it is not supposed to go in). When he explained his concern, I installed my Diagnostic Computer, and sure enough he had an ‘Oxygen sensor too lean’ code, but when I examined his engine I found the vacuum leak. Al I had to do was a slight repair with a vacuum hose worth 50 cents; clear the code in his computer and a road test after.
In this example the oxygen sensors had been performing properly, but they were not actually ‘lean’, instead that was their way of telling the computer that there was too much oxygen leaving the engine, the cause of this was the vacuum leak. The air inlet sensor did not know that extra air was entering the engine, but the oxygen sensor in the exhaust did notice the extra oxygen that was leaving the engine, from the emission program in the exhaust, this illuminated the ‘check engine’ light.
