Why Does Your Diesel Truck Keep Throwing Aftertreatment Codes?

If you’re constantly battling aftertreatment codes, you’re not alone. Today’s diesel trucks are loaded with emissions controls designed to reduce pollution—but they come with a price: complexity. And when something goes wrong in that system, your dashboard lights up like a Christmas tree. 

At Performance Diesel in Jackson, GA, we specialize in diagnosing and repairing the root causes behind those frustrating and persistent aftertreatment codes. Before you throw another sensor at it or schedule yet another regen, here’s what you need to know. 

What Is the Aftertreatment System? 

Your truck’s aftertreatment system is responsible for reducing emissions like nitrogen oxides (NOx) and soot. It works by processing exhaust gases through a combination of: 

● Diesel Oxidation Catalyst (DOC) 

● Diesel Particulate Filter (DPF) 

● Selective Catalytic Reduction (SCR) 

● Diesel Exhaust Fluid (DEF) system 

● Numerous sensors and controllers 

When even one of these components goes out of spec, your truck will throw a code—usually tied to performance loss, regen failure, or emissions non-compliance. 

7 Common Reasons Your Truck Keeps Throwing Aftertreatment Codes 

1. Clogged or Inefficient DPF 

A saturated diesel particulate filter is one of the most common causes of persistent codes like: 

● P2463 (DPF soot accumulation) 

● P2002 (DPF efficiency below threshold) 

Why it happens: 

● Too much idling or short trips 

● Passive regens not completing 

● Failed active or forced regen attempts

What to do: 

Schedule a DPF cleaning or replacement, depending on ash load and mileage. At Performance Diesel, we provide full DPF flow testing and regeneration services in-house. 

2. DEF Quality or Delivery Issues 

Faults like P207F or P20E8 often point to low-quality DEF, frozen lines, or a failing DEF injector. 

Why it happens: 

● Using off-brand or expired DEF 

● Contaminated tanks or crystallized DEF 

● Faulty DEF pump or level sensor 

What to do: 

Flush the system, use only certified DEF, and clean or replace sensors and injectors. We test DEF quality with digital refractometers to ensure it meets ISO standards. 

3. EGR System Malfunctions 

Though technically upstream of aftertreatment, a clogged or sticking EGR valve affects exhaust temperatures and composition, which can confuse DPF and SCR sensors. 

Codes it triggers: 

● P0401 (insufficient EGR flow) 

● P1403 (EGR performance issue) 

What to do: Clean or replace the EGR valve and inspect the EGR cooler for restrictions. Pair with a DOC inspection for full system health. 

4. Failed Temperature or Pressure Sensors 

Aftertreatment systems rely on precise exhaust temperature and pressure readings. If sensors fail or drift out of spec, you’ll get false codes like: 

● P0544 (exhaust gas temp sensor circuit) 

● P2459 (regen frequency abnormal) 

What to do: 

Use OEM-grade diagnostics to verify sensor readings. We never guess—we test first, replace only when verified. 

5. Incomplete or Interrupted Regeneration 

If regen cycles aren’t completing due to load changes or shutdowns, soot builds up and triggers codes like P242F or P244A.

What to do: 

Allow full regens on the highway when possible. Schedule forced regenerations at Performance Diesel when soot levels exceed passive or active limits. 

6. Software Calibration or ECM Glitches 

Sometimes, repeated codes aren’t from bad parts—but from outdated ECM software or improper calibration following component replacement. 

What to do: 

Check for manufacturer updates and reflash your ECM when needed. We offer full OEM-grade calibration and reprogramming at our Jackson shop. 

7. Tampering or Deleted Components 

If your system has been previously “tuned” or deleted, sensors may behave unpredictably—especially if not properly recalibrated. 

What to do: 

Have your system evaluated by a compliant shop like Performance Diesel. We don’t just clear codes—we ensure your truck meets EPA and Georgia DOT standards. 

What Happens If You Ignore Aftertreatment Codes?

Driving with unresolved codes isn’t just risky—it’s expensive. Here's what can happen: 

● Engine derate or shutdown 

● Failed DOT inspections 

● Fuel economy drops 

● Component damage (especially DPF and SCR systems) 

● Legal issues in emissions-regulated areas like Georgia 

Don’t Guess—Diagnose 

The biggest mistake we see is throwing parts at a problem without proper diagnostics. DPF issues, DEF faults, and SCR sensor problems can mimic each other—so guessing wastes time and money. 

At Performance Diesel, we use dealer-level software and emissions flow testing to trace the exact source of the code—and fix it right the first time. 

Learn More 

If your truck keeps throwing aftertreatment codes, it’s not just annoying—it’s a signal that your emissions system needs attention. With dozens of sensors and components working together, one failure can spiral into many. The good news? Most of these issues are fixable with the right diagnostics and service approach.

Trust Performance Diesel in Jackson, GA to find and fix the root cause of your aftertreatment codes—before they cost you a load, a fine, or an engine.