Understanding the specific actions that need to be taken when your check engine light comes on has become increasingly challenging for drivers in recent years. Much of the confusion surrounding different dashboard warning lights and light sequences is a result of advanced technologies for engine and emissions systems that were introduced in recent years. However, according to Ken Wilson, Director of Service Centers Development & Compliance , one rule of thumb hasn’t changed. “When the check engine light comes on, pull over.” 

The check engine light generally means the engine has gone through its self-diagnostics and needs to be checked as soon as possible. “While some lights are intermittent—turning on and off, or providing key-on codes or warnings,  continuing to drive with these warnings can lead to what's considered excessive codes, Wilson said. Wilson warns that continuing to operate an impaired engine can result in denied claims because the vehicle has been attempting to warn the driver that there is an issue. “If you’re not sure why the check engine light is coming on, the simplest way to find out is to check the owner’s manual for the particular fault code or warning,” he added. 

Common warning lights and triggers

Modern aftertreatment systems are a leading reason truck check engine lights come on. 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 higher.

Another common warning indicator is the DPF light. The DFP light comes on when the system needs to regenerate. When it’s flashing, the regen must be done while parked. A solid DPF light means you can do a parked regen or a passive one. According to a recent article in Overdrive magazine, to accomplish a passive regen, the exhaust needs to be at a specific temperature, which usually can be attained at highway speed. If the temperature is maintained for about 20 to 40 minutes, the regen will complete, and the light will go off. For the parked regen, ensure nothing is near the stacks where the heated exhaust will emerge. Follow your truck’s instructions to begin the process. The engine speed will increase enough to boost exhaust temperatures and complete the regen. As with a passive regen, it takes about 20 to 40 minutes for a parked regen to complete. 

“However, if you see the check engine light come on during DPF cleaning or regeneration, it’s possible that you could have a problem with fuel injection or the engine air management systems,” Wilson said.

A loose fuel cap is another common problem that can trigger a warning light. Fortunately, this one is an easy fix. If the fuel cap is loose after filling up, simply tightening at your next stop will do the trick. But what if you set it on the roof or to the side while filling up, forgot about it, and drove off? If you don’t replace it, you could find yourself making extra stops at the fuel station to fill up, as fuel leaks out and evaporates. 

What is it? And what does it mean? 

While some warning lights will differ, depending on the make, model and manufacturer of your truck, below is a brief guide to common engine warning lights and what they mean. 

• Check Engine Light - warns the driver to seek service soon. 

• Flashing Check Engine Light -  will flash for 30 seconds at key ON if maintenance is due.

• Malfunction Indicator Light (MIL) - warns the driver to schedule service soon (may light up in addition to other lamps).

• Red Stop Engine Light – the engine must be stopped as soon as it is safe to do so. 

• Flashing Red Stop Engine Light - driver has 30 seconds to stop the vehicle safely before automatic engine shutdown (if the Engine Protection Shutdown feature is enabled).

• High Exhaust System Temperature (HEST) Light - high exhaust temperatures may exist due to aftertreatment regeneration.

• Aftertreatment DPF Light - aftertreatment diesel particulate filter (DPF) requires regeneration. 

• Flashing Aftertreatment DPF Light - aftertreatment DPF requires regeneration; engine power may be reduced automatically. 

• Flashing Aftertreatment DPF Light and Check Engine Light - aftertreatment DPF requires immediate regeneration; engine power will be automatically reduced further.

• Red Stop Engine Lamp and Aftertreatment DPF Light - aftertreatment DPF regeneration has not been completed successfully in a timely manner.

Finally, while it’s rare, the check engine light may be incorrectly triggered without anything being wrong. The only way to be certain is to have your trucked checked out. Remember, ignoring the check engine or another warning light, or waiting too long, can risk further damage, costing you time and money if you experience a breakdown or a resulting claim is denied.