The Check Engine light means the Engine Computer detected a problem, set a diagnostic fault code, and since it is a problem that could adversely affect emissions, it turned the Check Engine light on to tell you. The first problem with continuing to drive it with that light on is there is always a long list of conditions that must be met to set a fault code, and one of those conditions is that certain other codes can't already be set. Many of the hundreds of tests the Engine Computer runs require sensor readings or operating conditions to be compared to each other. If something used for comparison has a problem and a fault code has been set, the tests that need that information will be suspended. There can be new problems that have occurred, but they won't be detected, and no fault code for them will be set.
Once you diagnose and repair the first problem, all of those suspended tests will resume. That's when any previously-unknown problems will finally be detected, fault codes will be set, and the Check Engine light will turn right back on again. Mechanics hate that because they can only provide a preliminary repair estimate for the fault codes they know about. They have no way of knowing there are additional undetected problems that need to be addressed. Car owners are frustrated because they wrongly assume the problem wasn't diagnosed properly or repaired properly. That frustration is much less likely to occur when problems are diagnosed and repaired right away.
The next issue is driving with the Check Engine light flashing. You can tell the relative severity of the problem by the way that light acts. If it goes out while you're driving, it's an intermittent problem, and it stopped acting up when the light went out. Those have relatively minor causes. If it's a little more severe intermittent problem, and it stops acting up while you're driving, the light will stay on until you stop the engine and restart it. With even more sever problems, the light will be on any time the engine is running, even when the problem is no longer occurring.
By far the most severe problems are when the Check Engine light is flashing. That means stop the engine as soon as you can to let the exhaust system cool down. Too much unburned gas is going into the exhaust where it will burn in the catalytic converter and overheat it. That can turn a minor problem into a really expensive one very quickly. The most common cause of too much unburned fuel is a spark-related misfire, and that would correlate with some of your other symptoms, mainly the hesitation.
Adding a can of some magic product to the gas is not going to solve a mechanical problem.
Monday, June 19th, 2017 AT 11:13 PM