Self Study Program 622 – Second generation Audi clean diesel

VAG SSP 622. This Self Study Programme describes the design and function of an exhaust gas aftertreatment system adapted for the use of AdBlue reducing agent.

Reducing the nitrous oxide content (NOx) in exhaust emissions is a global challenge facing automobile manufacturers, who are required to meet the new statutory limits set by the Euro 6 standard and equivalent international regulations on exhaust emission limits.

A modern “Selective Catalytic Reduction” (SCR) emission control system utilises the chemical synthesis product of urea (AdBlue) to reduce NOx emissions. In SCR systems, AdBlue reacts with the NOx  emissions to produce water vapour and nitrogen. NOx is short for nitrous oxide gases; they occur during the combustion process in diesel engines and are reduced by means of SCR  technology. ”

AdBlue is manufactured by a solution of a chemical called urea (also called carbamide) in water. Urea is a synthetic product which usually is made from natural gas and used in fertilizers, plastics and cosmetics. AdBlue is not made from recycled agricultural products. For exhaust gas aftertreatment in the AdBlue SCR system, the exhaust system requires additional components such as the heated catalyst1), the water-cooled metering valve, the diesel particulate filter with integrated DeNOx catalytic converter and the ammonia blocking catalytic converter.

AdBlue is a registered trademark of Verband der Automobilindustrie (VDA).

Learning objectives of this self study programme:

Once you have completed this Self Study Programme you will be able to answer the following questions:

Installed in a limited number of models only.

  • What is the function of the heated catalyst?
  • Which new sensors are integrated in the reduction system?
  • Why does the exhaust gas temperature have to be relatively high?
  • What is the function of the ammonia blocking catalytic converter?


  • Introduction
    • Emission standard
    • Audi models based on the Modular Longitudinal Matrix (MLB) with SCR system
  • Exhaust gas aftertreatment by an SCR system
    • Basic design (overall system)
  • Exhaust systems
    • Introduction
    • 1.6l / 2.0l TDI engine (EA288)
    • 3.0l V6 TDI engine
    • 4.2l V8 TDI engine
  • Fuel and reducing agent tank
    • Reducing agent tank
    • Audi Q7
    • Audi A6 ’11 and Audi A7 Sportback
    • Audi A4 ’14
    • Audi A8 ’10 and Audi A8 ’14
    • Swirlpot in active tank
  • Sensors and actuators
    • System overview (shown using the 3.0l V6 TDI engine as an example)
    • Reducing agent pump V437
    • Reducing agent tank sender G684 (level sender)
    • Particulate sensor G784 with control unit
    • Reducing agent injector N474 (metering valve)
  • Display strategy
    • Overview
    • Messages relating to reducing agent fill level
    • Fault warnings
  • Service
    • Tools
  • Annex
    • Self Study Programmes

The Self Study Programme teaches a basic knowledge of the design and mode of operation of new models, new automotive components or new technologies.
It is not a Repair Manual! Figures are given for explanatory purposes only and refer to the data valid at the time of preparation of the SSP. This content is not updated.
For further information on maintenance and repair work, always refer to the current technical literature.

Language: English
Format: PDF
Pages: 40

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