DPF SCR EGR and VGT Explained

  • Exhaust Gas Recirculation (EGR)
  • Diesel Particulate Filter (DPF)
  • Selective catalytic reduction (SCR)

Typical Vehicle Specification and Dates

  • Vehicles 2003-2007 Typically only had EGR
  • Vehicles 2008-2010 Typically had DPF and EGR
    Diesel Particulate Filter (DPF)
    Exhaust Gas Recirculation (EGR)
  • Vehicles 2011-2018 Typically had DPF EGR & SCR
    Diesel Particulate Filter (DPF)
    Exhaust Gas Recirculation (EGR)
    Selective catalytic reduction (SCR)

What is an EGR System (Exhaust Gas Recirculation)

An EGR valve is mounted on the exhaust manifold, its purpose is to regulate exhaust gases that go into the engine. A percentage of the exhaust gases are re-directed from the EGR cooler, through various pipes into the intake manifold where a temperature sensor, differential pressure sensor monitors the flow of the air coming in.

In later model years, the EGR system works with the VGT operation to create the right turbo drive pressures for the right amount of EGR Flow.

EGR systems on the older engine models do not have a VGT Turbo (2003-2007) so on these older models, the EGR operates in the same way, but without regulating the turbocharger.

What is a DPF System (Diesel Particulate Filter)

The exhaust DPF system consists of two parts designed to increase exhaust temperature for proper DPF regeneration. The after-treatment Fuel Injector (AFI), mounted on the exit pipe from the turbocharger, injects diesel into the exhaust stream during a regeneration cycle.

When the fuel meets the (DOC) Diesel Oxidation Catalyst, a chemical reaction is started, and as a result the exhaust system temperature increases to a level that oxidizes the soot in the filter reducing exhaust emissions.

DPF System Failures

Under normal engine operation, the DPF collects the soot and other particulate matter. These will be eventually oxidized using a regeneration process.

The DPF filter can show signs of failure, including but not limited to

  • Temp Regeneration Lockout
  • Forced Regeneration Needed
  • High Soot Load with associated Fault Codes
  • Active DPF Fault Codes
  • Excessive fuel consumption
  • Loss of Performance

DPF System including SCR, EGR and VGT

This system will have the SCR, DPF filter, EGR and VGT turbocharger to regulate emissions.

The SCR technology allows for passive regeneration which is triggered when the EGT (Exhaust Gas Temperature sensor) at the DPF inlet and the NOx to soot ratio are high enough to oxidize the accumulated particulate matter. The process is slow but does not change the engine operation.

With this system, forced regeneration (stationary) is a backup option when passive regeneration is insufficient. The soot ratio will increase and decrease depending on the operation of your system.

VGT Turbo Charger

The VGT regulates the charge pressure and drives the (EGR) system.

Speed of turbocharger is controlled by an electronic actuator and will adjust based on engine load conditions.


  • Lowers emissions
  • Better fuel consumption
  • Increased power output


  • Active Faults for VGT
  • No pulling power (limp mode)
  • Costly repairs
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