It’s no secret that the modern automobile is more complicated than ever. All one needs to do is open the hood and see the maze of wiring that controls these complex beasts. Such complexity is to be expected, however, as today’s engines are more powerful and more efficient than they’ve ever been.
For example, the 2.9-liter four-cylinder engine that powered the 1912 Ford Model T Runabout produced a scant 20 horsepower. On the other hand, a modern-day experimental Nissan engine, the 1.5-liter three-cylinder DIG-T R, with half the displacement of the Ford, puts out 400 horsepower. Even the 2012 Toyota Camry’s 2.5-liter four-cylinder produces 178 horsepower, nine times greater than that of the Ford. That’s not bad for a century of automotive development, but such advancements only have been possible as a result of advanced fuels, engineering, lubricants and fine computer controls, which brings us to nearly every car owner’s lament, the check engine light.
What is the Check Engine Light?
Having electronic controls is one thing, but how does a driver know that the vehicle is functioning properly? Usually, a diagnosis would be tied to symptoms, such as rough idle, misfire or excessive fuel consumption. But what about non-drivability problems, such as those related to evaporative emissions, nitrogen oxides and fuel trim? The check engine light, also known as malfunction indicator lamp or service engine soon light, is a visual indicator to the driver that one of the electronic controllers has detected a malfunction.
In the late-1960s and early 1970s, the first electronic controls with on-board diagnostics (OBD) became available, which allowed technicians access to basic engine data. These early systems were specific to each automaker, however. Eventually, standardized OBD systems began to appear, through the 1980s and early-1990s, with expanded capabilities and diagnostics, but still unique to each automaker. On vehicles produced since 1996, industry-standard OBD-II (OBD 2nd Generation) was standardized across automakers, making diagnostics easier to access across the board.
With a diagnostic scan tool, a technician or DIYer can read diagnostic trouble codes from the engine control module or other modules, depending on the capabilities of the scan tool. Any retrieved trouble codes can lead the technician on a certain diagnostic path, but they do not tell the technician what to replace, merely what the engine control module is seeing. For example, P0301 is defined as “Cylinder #1 Misfire,” but it would be up to the technician to determine the cause and corrective measures necessary.
My Check Engine Light Came On. Now What?
If the check engine light comes on, don’t panic. At the same time, even if the engine and transmission seem to be “running fine,” don’t ignore it. Usually, when the light comes on, it will put the engine in “limp-home mode,” also called open-loop or fuel backup mode. In this case, the engine control module goes into a basic mode of operation that may reduce engine power, limit automatic transmission function or increase fuel consumption. Driving around in this mode will cost you more in fuel and will increase emissions. In states that require an emissions inspection, the vehicle will fail.
If the check engine light is blinking, you should pull to the side of the road safely and shut the engine off. The blinking light means that the malfunction is significant enough to cause damage to the catalytic converter. Shutting off the engine at this point might save you hundreds, even thousands, of dollars in catalytic converter replacement costs. Have your vehicle towed to a trusted technician for diagnosis and repair. Whatever repairs are necessary will almost certainly be cheaper than replacing an expensive catalytic converter.
If the check engine light is steady, you should call your trusted mechanic to set up an appointment for diagnosis and repair. It’s not an emergency, but the EPA reports that every mile you drive could cost you as much as 40 percent more, depending on the fault.
Were you Paying Attention?
Many times, simply being observant can go a long way toward an efficient and successful diagnosis. To the best of your ability, try to recall the events leading up to the check engine light coming on.
Some questions to ask yourself:
- Was this first thing in the morning, or after sitting all day?
- Did you just fill up the fuel tank?
- What was the fuel level?
- Have you been in city traffic or on the highway?
- Were you towing or hauling?
- What’s the weather like – hot, cold, sunny, rainy?
It’s OK if you can’t answer all these questions, but it can be surprising sometimes how even small details can affect the direction your technician might take to get to a successful diagnosis. The more information you can provide, in addition to the information the technician can extract, the faster you’ll get back on the road.