By now we’re all aware of the infamous check-engine light, as well as other annoying dash lights. But do we really know what they mean? Let me help. The MIL, or malfunction indicator lamp, is a dash light which can only come on if a problem exists which could cause higher-than-allowable tailpipe emissions. The car may or may not exhibit symptoms noticeable to the driver. Many problems can exist which won’t affect the drivability. The federal government mandates what can and can’t illuminate the light. There’s enabling criteria for each specific vehicle which must be met before the light turns on, and once it’s illuminated the vehicle’s on-board diagnostic system stores trouble-codes which indicate the problem area. A very common myth we experience at the shop is when the customer thinks the technician can simply hook up the computer and be told which part to replace. It certainly doesn’t help this myth when large, national-chain auto parts stores offer free code-reading in hopes of selling the customer a part which they may or may not need. There are so many different possibilities which can turn on the light, and the code only refers to the circuit which is having the problem. Think of it like a doctor visit. When we go to the doctor we tell them what symptoms we’re having. Often, the doctor then has to run a few tests to determine the exact cause, and even then, it’s sometimes only an educated guess, albeit a very good guess. With cars, we use the same approach. Once we’ve communicated with the vehicle and researched the code or codes, we then perform a few tests. Depending on the symptoms, we examine data using our computer interface with the car running or not. We measure voltages, amperages, and volumes. We drive the car. We visually inspect areas which are often hidden and require removal of other components for access. These tests take time, tools, and education, and therefore cost money. Finally, we can create an estimate for the cost of repair once we determine the actual problem. It really is as complicated as it sounds, and our technicians deserve a lot of credit. Their job is incredibly difficult, and no amount of schooling can quite prepare them for the complexity of their job.
As I mentioned, the vehicle often doesn’t show symptoms when there’s a problem, but it’s still important to fix the problem. With nearly 250 million cars on the road in the U.S., it’s imperative we all do our part to reduce the footprint our vehicles make. I know how annoying that light is, and the relief I feel when I get it to turn off. As an Audi driver, I sometimes think my MIL won’t ever turn off! But it will, once it’s tested and fixed properly. We want to be warned when there’s a problem, and we may not know if a serious problem is developing if we are constantly ignoring the light. As always, a solid relationship with your professional and certified shop will serve you well. They can advise you and give you the assurance you need to move on to your next destination.