My sentiments exactly. I would buy a new car if it didn't have all of these ridiculous, unnecessary, unreliable computers hung onto every possible system, BUT, in the case of air bags, anti-lock brakes, and especially engine controls, there are real benefits and their cost is outweighed by those benefits. In this case you are to blame for your aggravation. Thanks to Chrysler's first use of electronic ignition in 1972 and computer controlled timing in 1976, engines run much cleaner and need fewer tune-ups. Thanks to electronic fuel injection, fuel mileage has gone up substantially. With those computer controls, there are more sensors and more things to go wrong. To make diagnosing a circuit with a defect easier and faster, the Engine Computer constantly runs self-tests on those systems, and it records a diagnostic fault code when it sees a problem. Those codes never say to replace a part or that they're defective, but they do lead you directly to the circuit or system that needs further diagnosis, or they indicate the unacceptable operating condition.
Things got more complicated in 1996 when they started monitoring the efficiency of the catalytic converters in the exhaust system. At the same time they began running self-tests for gas fumes evaporating from the fuel system. That adds another level of complexity by indicating problems related to two systems that have nothing to do with how the engine is running, BUT, it makes the exhaust so clean you can suck on the tail pipe and live to tell about it. That's a real big benefit.
Three things happened when you purposely ignored the Check Engine light. First of all, the majority of the problems detected have very minor causes that if left unrepaired, will turn into major problems. You did yourself a huge disservice by ignoring that warning. Second, even if you have the fault code read and choose to ignore it because it's relatively minor, if a second, totally unrelated, and serious problem develops, you'll never know it until it's too late because the warning light is already on. The problem could be a simple one resulting in too much raw fuel going out the exhaust system, wasted. That can overheat the catalytic converter and over time melt the catalyst and it will become plugged or ineffective. That's a very expensive repair.
Third, and most importantly, to set any fault code there is always a long list of conditions that must be met, and one of those conditions is that certain other codes can't already be set. The computer compares many things to each other to verify they're working properly. For example, it knows that after the engine has been off for at least six hours, the coolant temperature sensor and the intake air temperature sensor had better be reading the same temperature. If they are not, it has to figure out why or which one is wrong. If a problem is detected for the coolant temperature sensor, the computer knows it can't rely on those readings to compare to the intake air temperature sensor, so it suspends those self-tests. If a problem develops with the air temperature sensor, it is possible no fault code will be set, and your mechanic will not know about that second failure. It's not until the coolant temperature circuit is fixed that the self-tests on the air temperature sensor will resume. THAT'S when the problem is detected, the new fault code is set, and the Check Engine light turns on again. Usually the Check Engine light turns on with the new fault code right after the first problem is fixed, and you incorrectly think the mechanic didn't fix the problem properly. In reality, he had no way of knowing that second problem existed. That is your fault for ignoring the warning light for so long. The longer you ignore the warning light, the more time passes for additional problems to occur that no one will know about, ... Yet. A problem could also occur that has a serious affect on how the engine runs or fails to start, but if no fault code sets related to that new problem, there is no chance of knowing which circuit to even start looking in. You have to diagnose and fix the first problem first, (the one you chose to ignore), then HOPE the second problem will set a fault code, so you know where to start looking. Some fault codes related to no-start conditions only set when the engine stalls and the car is coasting to a stop. They may not set after the first problem is fixed and you're cranking the engine. Now you'll be paying for a lot more of your mechanic's time as he tries to figure out where to start looking. That added expense could have been avoided if you had just fixed that first problem years ago.
Also be aware there are well over a thousand potential fault codes the Engine Computer can store, and only about half of them make the Check Engine light turn on. Those are the ones that could adversely affect emissions. That means that by ignoring the light, you were getting worse fuel mileage all that time, and / or your car was polluting the air more than normal. I don't know who told you to ignore the warning light but that is the stupidest thing to tell a car owner. Replacing the fuel filter will definitely not cause the warning light to turn off. The fuel supply system isn't even monitored by the Engine Computer so it has no idea if a problem exists there. Even if it could set a fault code related to the fuel filter, for what possible reason would you not replace it? There are some fault codes that will self-erase if the problem goes away, but that isn't the type of code that was set if the light was on "for years and years". The same defect probably still exists that has always been there, and it's probably relatively minor, and your mechanic probably erased it with a scanner so the light would reset and turn off. Minor problems could easily take a month to show up again, and rather than find out what that simple cause is, you want to ignore it again and complain about it because you're lucky the engine is still running okay. At the very least, find out what the fault code is so I can suggest some possible causes and fixes, and give you some ideas on how to diagnose the cause. Your car has a defect and the Engine Computer knows what is wrong. NO ONE who understands cars would ignore that, especially for years.
Sunday, January 12th, 2014 AT 4:04 PM