Modern diesel vehicles use several systems to control emissions. The Diesel Particulate Filter, Selective Catalytic Reduction and AdBlue/DEF dosing system each have different functions, but faults in one area can affect the others.
DPF: controlling particulate matter
The DPF captures soot from the exhaust. The control system monitors values such as differential pressure, temperature and calculated soot loading to determine when regeneration is required.
SCR and AdBlue/DEF
SCR reduces nitrogen oxides by injecting a urea-based fluid into the exhaust. The system can include pumps, heaters, injectors, NOx sensors, temperature sensors and control modules.
Start with fault codes, not replacement parts
A diagnostic scan provides direction, but a DTC does not always identify the failed part directly. Technicians should review live data and test the related electrical, fluid and exhaust conditions.
Check the physical system
Leaks, damaged wiring, blocked lines, poor connectors, exhaust leaks and sensor contamination can all produce misleading symptoms. Visual inspection remains essential.
Regeneration problems
A DPF that does not regenerate may be the result of another engine or sensor fault. The root cause should be corrected before repeatedly forcing regeneration.
Use correct service procedures
Adaptations, resets and component replacements should be performed only when supported by the diagnostic procedure and after the actual fault has been repaired.
VM DIAG diagnostic support
VM DIAG supplies diagnostic tools and technical support for supported passenger and commercial diesel systems. Our focus is accurate diagnosis and correct workshop procedures, not bypassing emissions-control systems.
