Now, I will try and explain another light that is very confusing and that is the CHECK ENGINE or SERVICE ENGINE SOON light. (Usually orange, meaning CAUTION IS REQUIRED.)

This light DOES NOT mean that you are supposed to stop and see if the engine has any oil in it.
This light DOES NOT mean that you should stop and see if the engine is still there.
This light DOES NOT mean that the engine is due for an OIL and FILTER change.

This light is designed as a warning to the driver that the On-Board computer has pick up a problem it one of the systems that it monitors. (Having to do with how the engine runs.) The Computer system constantly monitors the information that it is getting fed from different sensors and as soon as it suspects a problem, the WARNING light is turned on. As the warning light is turned on, the computer registers a TROUBLE CODE in its memory to let a person testing the system know which area MAY have a problem. BUT, (And that is a BIG BUT.) it is very possible that your vehicle may have a problem and the light does not turn on. So, you can NEVER ASSUME that because the light isn't on, that there is NO PROBLEM. (Remember what the BASIC interpretations of assume is.) Nor can a Mechanic ASSUME that there are no problems just because when they scan the On-Board, they could not get any trouble codes.

Let me give you as simple an explanation as I can by using the Coolant Temperature sensor. This sensor tells the Computer what the temperature of the engines coolant is, in degrees. When the sensor picks up a temperature of say 180 degrees, it sends that information to the computer and the computer adjusts fuel control for THAT temperature. BUT, (And again a BIG BUT.) who is to say that the sensor is sending the RIGHT INFORMATION TO THE COMPUTER? However, this situation is very easy to confirm and would just require that a thermometer be placed in the Radiator, to see if the engine coolant was in fact at the same temperature that the sensor is reading. (I have seen coolant sensors telling the computer that the engine is OVER 200 degrees when in fact the engine was at 50 degrees and cold.) This type of situation WOULD NOT REGISTER A TROUBLE CODE AND IT WOULD NOT TURN ON THE ENGINE LIGHT. This works the same for ALL sensors in the system and I know a lot of people have a problem trying to figure that out. I have heard of Mechanics that would tell a customer that there COULDN'T be anything wrong with their car because the computer does not have any trouble codes. A throttle position sensor can think the car is at full throttle, when in fact it is at Idle. An oxygen sensor can think that the fuel mixture is CORRECT, when in fact the engine is using TWICE as much fuel as it should. And I could go on and on but I think you are getting the idea. (Know, Back up and read this AGAIN, just to make sure that you understand what I am trying to explain.) Just like the computer sitting in front of you that you are using to read this, a computer is fed information and then it can be PROGRAMMED to deal with that information. FALSE INFORMATION WILL PRODUCE FALSE RESULTS. Any questions???????????????????

"TOOT" Rick "The Wrench" - July 11th,1999
Copyright of Rick The Wrench, 1999