Volkswagen Passat 2012 Service Training page 25

Selective Catalyst Reduction
The 2012 Passat uses a Selective Catalyst Reduction (SCR) system for treatment of the exhaust gases. The
system is very similar in components and function to the 2011 Touareg 3.0L TDI Engine.
When the exhaust gases exit the engine, they pass through the oxidation catalyst and diesel particulate fi lter. This
component converts gases and traps the soot in the oil. The soot is burned off through regeneration cycles.
After exiting the oxidation catalyst/diesel particulate fi lter assembly, the gases are sprayed with a reduction agent
(urea) using the SCR injection valve. The gases then enter the SCR reduction catalysts where the Nitrogen Oxide
(NOx) emissions are reduced substantially.
A NOx sensor downstream of the SCR reduction catalysts monitors the effectiveness of the NOx reduction and is
used to infl uence the amount of reduction agent used.
The exhaust throttle pictures is not used for the SCR process. It is used for the low-pressure exhaust gas
recirculation process. More information on the operation of the low pressure EGR can be found in the 2.0L CR
TDI BIN5 SSP 826803.
Oxygen Sensor
Low Pressure EGR
Recirculation Filter
SCR Injection Valve
Oxidation Catalyst
Particulate Filter
Exhaust Temperature Sensor
Exhaust Throttle
Engines
SCR Reduction Catalyst
NOx Sensor
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