Repair manual

SULEV 2.0L TFSI Engine
35
Natural Frequency Based Oxygen
Sensor Control
Task
The task of this system is to maximize utilization of the
primary catalytic converter during the conversion of
pollutant gases.
Function
Oxygen Sensor G130 LSF4.2 downstream of the primary
catalytic converter supplies the ECM with a voltage signal
(nonlinear) indicating “rich” or “lean.”
Heated Oxygen Sensor G39 LSU4.9 determines a
frequency from the flow rate and the condition of the
catalytic converter. The ECM provides this frequency with
an amplitude indicating whether the mixture is to be
“rich” or “lean.”
If the primary catalytic converter is supersaturated with
oxygen (lean mixture), Oxygen Sensor G130 will send
the ECM a nonlinear signal indicating the lean mixture
condition.
The mixture is then enriched with fuel until the oxygen
has been “displaced” from the catalytic converter. This
condition, in turn, is registered by Oxygen Sensor G130 as
a nonlinear signal indicating the rich mixture condition.
The mixture is then leaned out by the ECM. If the
nonlinear signal is received again, the mixture will
again be enriched. The frequency, or period, during
which the mixture is enriched or leaned out is variable,
being dependent on the gas flow rate (engine load) at
that moment. However, aging of the catalytic converter
(decrease in conversion rate) also reduces the frequency.
A large proportion of the exhaust gases is converted in
the primary catalytic converter. The remaining exhaust
gas constituents are then converted to non-toxic gases
by the underbody catalytic converter.
Oxygen Sensor 3 Behind Three Way Catalytic Converter
G287 (downstream of underbody catalytic converter)
operates in much the same way as a conventional linear
oxygen sensor.
Its task is to control the fine adjustment of Heated
Oxygen Sensor G39. For this purpose, the characteristic
curve is corrected by the trimming control in the ECM.
It also monitors the conversion process in the catalytic
converters.
Reference
For basic information on exhaust emissions
and engine management systems, please
refer to Self-Study Programs 943003 Motor
Vehicle Exhaust Emissions and 941003
Engine Management Systems.