Why is My Truck’s Check Engine Light On?

You’re driving down the highway, when you realize that the check engine light is illuminated. Maybe you saw it light up at that very moment, or perhaps it has been illuminated for some time and you’re just now noticing it. Oftentimes, the reason for seeing the check engine light is minor. Regardless, the issue requires an inspection and resolution.

Pinpointing the Cause

There are many different reasons for a check engine light to illuminate, and the list continues to grow as electronics and emissions controls in trucks become more sophisticated. The Electronic Engine Control System functions on fault codes, meaning that the system essentially monitors itself and illuminates the check engine light when it finds a problem. Some fault codes are proprietary to the make of the engine and truck. If either the engine controller or some other module senses something wrong, a specific fault code will trigger the check engine light. These codes make it easier to identify the problem system.

Aftertreatment Issues

One of the most common reasons for seeing the check engine light is the aftertreatment system. Diesel trucks have a nitrogen oxide (NOx) sensors, similar to the oxygen sensors in a car. Before the catalyst, the NOx sensor measures parts per million of NOx being produced by the engine. To ensure the catalyst is performing properly, the NOx sensor compares the reading taken after the catalyst. If the engine does not see a sufficient change in NOx ppms, it will set a code for NOx efficiency. This will cause the engine light to illuminate and the engine will eventually reduce engine power until the problem is resolved.

In 2007, the United States Environmental Protection Agency (US EPA) regulations caused engine manufacturers to add diesel particulate filters (DPFs) to its aftertreatment standards. In 2011, more changes in regulations prompted engine manufacturers to add diesel exhaust fluid to lower NOx levels. These regulations have made engine electronics and engine management more complex, which means more things can go wrong. In turn, the chances of seeing the check engine light are inherently higher.

Passive DPF Regeneration

DPF cleaning or regeneration normally happens when you are driving under certain conditions. If you are driving on a highway at a specified load, vehicle speed and the soot levels or pressure differential across your filter are high, fuel will be injected into the exhaust to clean help burn out the soot collected by the particulate filter. While this helps to burn the particulate being gathered, it can also raise exhaust temperatures and trigger a different light in newer models. Don’t confuse a high exhaust systems temperature (HEST) light with the check engine light; the former simply tells you that a regen is occurring and the exhaust temperature is high. Manufacturers want you to know this out of an abundance of caution, so you avoid fire and heat hazards (such as parking on a pile of leaves or next to a car with a plastic bumper). Nevertheless, if you do see the check engine light come on, it is possible that a problem with fuel injection or engine air management can also be a potential factor.

Don’t Ignore It

The check engine light is rarely an urgency, but always requires attention. If you see it illuminated in your truck or bus, visit the repair specialists at On-Site Fleet Service. With four locations throughout New Jersey, we’re always nearby when you’re driving the Garden State roads and highways. Click here to learn more about our services.

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