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Introduction
If you’re running a diesel truck or heavy equipment, you know how important the emissions system is for keeping your engine compliant and running efficiently. But these systems can cause major downtime when something goes wrong. At AftertreatmentParts.com, we’ve helped thousands of customers diagnose and solve emissions issues—here are the most common problems they run into and what to do about them.
1. DPF Clogging or Failure
Search terms: "DPF clogged symptoms", "diesel truck black smoke", "how to clean DPF"
A clogged Diesel Particulate Filter (DPF) can cause poor engine performance, increased fuel consumption, and regeneration failure. You might see warning lights or excessive smoke. In many cases, the DPF needs cleaning or full replacement.
✅ Fix: Clean the DPF if caught early, or replace with an OEM-quality aftermarket unit.
2. Failed NOx Sensors
Search terms: "NOx sensor fault code", "NOx sensor location", "how to test NOx sensor"
NOx sensors monitor nitrogen oxide levels in the exhaust. When they fail, you'll likely get codes like 3238, 3242, 5024, or other DEF system faults.
✅ Fix: Replace faulty upstream or downstream NOx sensors with high-quality replacements.
3. DEF Pump or Dosing Valve Issues
Search terms: "DEF pump not working", "DEF dosing valve stuck open", "DEF system failure"
If your DEF pump isn’t working or your dosing valve is clogged, your system won’t inject fluid properly, triggering derate conditions and warning messages.
✅ Fix: Diagnose whether it's the pump, valve, or wiring. Replace components with tested replacements to restore operation.
4. DEF Quality or Contamination Problems
Search terms: "DEF fluid contamination", "bad DEF symptoms", "how to test DEF quality"
Contaminated DEF fluid (often from poor storage or improper topping up) can damage sensors, clog injectors, and trigger costly repairs.
✅ Fix: Drain and flush the system. Always use certified DEF and replace the filter regularly.
5. Faulty Temperature or Pressure Sensors
Search terms: "DPF pressure sensor code", "exhaust temp sensor failure", "how to test temp sensor diesel"
These sensors monitor flow and heat through the emissions system. Faulty readings can trigger false fault codes and cause unnecessary regens.
✅ Fix: Replace damaged sensors promptly to restore accurate system monitoring.
6. Constant Regeneration Cycles
Search terms: "DPF keeps regenerating", "frequent regen cycles", "regen every day diesel truck"
Frequent regenerations often point to an underlying problem like low exhaust temperatures, poor sensor data, or an overloaded DPF.
✅ Fix: Investigate root cause. Cleaning or replacing the DPF and ensuring all sensors are functional is key.
7. Engine Derate Due to Emissions Faults
Search terms: "engine derated due to DEF", "50% power emissions fault", "how to fix engine derate"
A derate is a protective measure when the system detects emissions faults, cutting your power to prevent damage or compliance violations.
✅ Fix: Use a diagnostic tool to pull codes. Replace failing parts—common culprits include NOx sensors, DEF pumps, or pressure sensors.
Conclusion
Emissions system issues are one of the most frustrating problems for diesel operators—but with the right parts and fast shipping, they don’t have to keep you down for long.
👉 Need help identifying your fault code or finding the right part?
Contact us at AftertreatmentParts.com — we offer expert support, fast shipping, and free delivery across North America, including overnight options!