Audi 4.2-litre V8 FSI, Service Training

Page: 34 / 48

34
377_043
Operating mode in the Q7
During the warm-up phase, the engine control
unit J623 activates secondary air pump V101 via the
secondary air pump relay J299.
The air flow from the secondary air pump opens the
combination valve for secondary air and admits air
into the exhaust system upstream of the catalytic
converter.
Secondary air system
The secondary air system ensures that the catalytic
converter heats up more quickly and is available
sooner after a cold start.
Principle
Due to the richer air-fuel mixture in the cold start
and warm-up phases, a higher concentration of
unburned hydrocarbons occurs in the exhaust gas.
Post-oxidation in the manifold and headpipe is
promoted by secondary-air injection.
The heat dissipated during this process heats the
catalytic converter to operating temperature within
approx. 30 seconds after engine start.
Exhaust system
Air filter
Combination valves
(self-opening)
Secondary air system in the Q7
Secondary air pump