Q – The check engine light came on in my 2001 Boxster and I wonder why. The car still seems to run well and with no symptom present, I think it is OK to drive but that light bugs me. When I called the shop, they said as long as it is not flashing, I could drive it in.
A – When the “Check Engine” light is on but not flashing you are usually correct. With no symptom I would not worry about it. I would call it more of a justifiable concern. When you take it in, you should expect your advisor to test drive the car and note their observations and recommend a “computer scan” and reset.
The technician will access the vehicles OBD II interface, extract & save the stored codes and print out a report. If your advisor is knowledgeable about the topic they will then recommend a proper course of diagnosis appropriate for the fault codes. When there is no symptom present, the best course of action might be to clear the codes and attempt a reset, sort of like closing a program on your computer and restarting it.
Following a reset, then your adviser should test drive to confirm that the symptom is gone and that the codes do not immediately reassert themselves. When codes come back right away, I call that a “hard fault” and I would suggest that those be investigated using technical service bulletins and a diagnostic trouble tree provided by the manufacturer. Hard faults are sometimes easier to track down.
The tricky ones are the “soft faults” or intermittent faults where the code may not come back for a number of miles, days, weeks, or longer. Occasionally I will drive a car with the computer attached and take live readings from various sensors during a road test to try and catch the car “in the act”. I do not actually take the readings, I have an assistant do it. Multi-tasking while driving is not an acceptable diagnostic process!! The tricky soft faults sometimes involve 10 to hundreds of miles. To have a client with the understanding of this process and a desire to get to the bottom of the problem is most appreciated.
The important thing to remember is that the code extraction and reset operation is intended to access the vehicles fault memory, retrieve and analyze stored codes and it is just the first step in a diagnostic process. Unless there is a “phantom” code, it will not correct most issues.
So the good news is that your car is still running well and the bad news is that in most cases, the check engine light will come on again. If and when it does, I would then recommend spending some diagnostic time to determine why. I usually do not suggest spending any more time on a check engine light unless the fault is repeatable, if further problems can occur if ignored, and if you have the budget for it.
If you ever notice that warning light flashing that is another story. A flashing check engine light indicates a problem that could potentially damage the car, and
In that case, pull over and strongly consider other options for getting the car in to the shop. If that flashing light is accompanied by reduced performance, odd thrashing noises or smoke, you already know the answer to this one. MC