First of all, let me explain how that light works. The Engine Computer detected a problem, set a diagnostic fault code, then turned the light on to tell you. Your mechanic can erase the code but that doesn't fix the problem that set the code. The computer is going to see that problem again and set the same code.
There's well over a thousand possible codes, but only those that could adversely affect emissions must turn on the Check Engine light. The place to start is by having the code(s) read. Many auto parts stores will do that for you for free. Understand too that those fault codes never say to replace parts or that they're defective. They only indicate the circuit or system that needs further diagnosis. Those guys understand selling parts, but first we need to know the exact code number.
Another thing that is real frustrating for car owners AND mechanics is there is always a long list of conditions that must be met to set a code, and one of those is that certain other codes are not already set. The computer constantly compares various sensor readings and operating conditions to each other so it knows when one of them is wrong. If a code is already set for one thing, anything else that needs that information for comparison doesn't have anything reliable to go by, so no additional codes will be set. Those codes are all your mechanic has to go on to begin any diagnosis. Once the first problem is diagnosed and repaired, the computer will resume its self-tests. THAT'S when the next code can show up and the Check Engine light will turn on again. You will assume incorrectly that the problem wasn't diagnosed or repaired properly, when in fact, there is a second, different problem the mechanic had no way of knowing about. It doesn't sound like you have this frustrating issue but it's worth mentioning.
The place to start is by having the codes read. You don't want to erase it until the cause is fixed, THEN the light may turn off on its own. Relatively serious codes will keep the Check Engine light turned on even after the cause is fixed. For those, all that is needed is to manually erase it with a scanner or code reader.
Tuesday, October 8th, 2013 AT 12:16 AM