This class covers emission control system mandated on today’s modern diesel engines. The diesel oxidation catalysis (DOC), Diesel Particulate Filter (DPF), and the Selective Catalysis Reduction (SCR) (DEF) systems are plagued with problems. When a DPF regenerates too often, not at all, or has chronic Diagnostic Trouble Codes (DTC’s) what diagnostics procedures will help the technician find the root cause of the problem? How about the SCR system’s faults? Ammonia Slip problems can cause a vehicle to be down for days, what causes Ammonia Slip? Normal regeneration and NOx reduction begins upstream of the after treatment.


In class, we cover:

  • How a small amount of face loading causes DOC’s, DPF’s, and SCR’s to be inefficient, setting multiple DTC’s that you have to deal with.

  • The operation of the DOC, DFP, and SCR systems as well as their components.

  • How the DOC efficiency is tested and what to do about DOC efficiency DTC’s.

  • DPF regeneration detection.

  • Soot loading faults.

  • How DOC problems cause the DFP to fail.

  • Why the DFP won’t passively, actively, manually, or force regen.

  • Why the computer fails to see regeneration requirements.

  • What goes wrong when regeneration can’t complete.

  • The root causes of ammonia slip and its effects on the system.

  • DEF delivery problems.

  • How the system fails to reduce NOx by crystallization of the DEF.

  • How the DPF can cause crystallization.

  • Why the system fails to reduce NOx in the SCR catalyst.

  • The reasons the dosing valve fails to inject the correct amount of DEF.


Normal Selective Catalysis Reduction is dependent upon a normally working Diesel Particulate Filter which is dependent upon a normally working Diesel Oxidation catalysis. All three after treatment systems are dependent upon normal up stream operation. The entire system is linear. Small upstream problems cause large after treatment problems. Attend the training class to avoid diesel emission headaches.


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