Aftertreatment problems are some of the most frustrating issues in diesel repair. They can cause derates, warning lights, failed regens, high repair bills, and repeat shop visits.
The diesel particulate filter, SCR system, DEF system, NOx sensors, temperature sensors, pressure sensors, doser, and related controls all have to work together. When one part of the system fails, the truck may protect itself by limiting power or triggering a derate.
A diagnostic scanner can help technicians evaluate:
- Soot load
- Ash load
- DPF differential pressure
- Exhaust temperature sensor readings
- NOx sensor values
- DEF quality or level data
- Regen status
- SCR efficiency
- Active and inactive aftertreatment codes
The mistake is jumping straight to a forced regen. A regen may be helpful when conditions are correct and the system supports it. But if the truck has active faults, sensor failures, poor engine performance, exhaust leaks, or other unresolved issues, a regen may fail or create more confusion.
Good diagnostics ask better questions:
- Why did the DPF load up?
- Is the engine producing too much soot?
- Are the temperature sensors reading correctly?
- Is the differential pressure sensor accurate?
- Is the DEF system dosing properly?
- Are there active faults blocking regeneration?
- Has the truck already been derated?
For shops, aftertreatment diagnostics can be profitable when handled correctly. For fleets, catching these issues early can prevent roadside failures. For owner-operators, a scanner can provide visibility before the truck ends up in a derate situation.
