How Do You Know If Your Truck’s DEF Injector Is Faulty?

If you drive a relatively new truck, you probably already know that your rig uses a diesel exhaust fluid (DEF) system to reduce emissions. These systems may also go by other names, such as selective catalytic reduction (SCR) or aftertreatment. Whatever the name, these systems all work by utilizing a consumable fluid to convert your truck's nitrogen oxide (NOx) emissions into water and nitrogen.

Aftertreatment systems consist of several separate filters that help reduce and convert the harmful gases in your truck's emissions. The SCR system is the final stage, and this is where your exhaust fluid mixes with NOx gases to reduce them into harmless substances. The whole system relies on a DEF injector to add a fine mist of exhaust fluid into the exhaust gas stream.

What Happens If Your DEF Injector Goes Bad?

Your truck's DEF injector works by delivering a precise amount of exhaust fluid to create the necessary chemical reactions in the SCR system. Unfortunately, DEF injectors can suffer from similar failures to fuel injectors. If the nozzle becomes clogged or corroded, it can no longer deliver the appropriate amount of exhaust fluid to keep your DEF system working correctly.

DEF fluid that doesn't correctly mix with your exhaust stream can cause numerous problems for your truck's emission system. Without enough fluid entering the exhaust, your SCR system will take longer to convert nitrogen oxide and ammonia into nitrogen and water. The system will also fail to reach the correct temperatures, increasing regen time for your diesel particulate filter (DPF).

Faulty DEF injectors can produce a range of symptoms, including excessive DEF usage and various check engine codes relating to the aftertreatment system. While the aftertreatment system isn't necessary to keep your engine running, your truck's computer will likely "de-rate" if the problem is severe enough. This mode will prevent you from driving at highway speed or may even disable the engine.

What Should You Do About a Faulty Injector?

Your truck's DEF injector is a relatively inexpensive component that's usually accessible and easy to repair. While any failure can be frustrating, having your truck de-rate itself can be a far more severe (and costly) inconvenience. If you notice an increase in DEF usage or you begin to receive aftertreatment-related check engine codes, it's crucial to get your truck into a service shop as soon as possible.

In addition to risking an engine de-rate, waiting too long to fix this problem can cause more problems with your aftertreatment system or create clogs in your particular filter. Fortunately, a qualified diesel mechanic should be able to quickly identify a faulty DEF injector and get your truck running again. 

For more info, contact a local semi-truck repair services company.