Volvo 960 Owner's Manual page 229

1996 Volvo 960
Heated oxygen sensor
This is an emission control system designed to reduce emissions and improve fuel economy. The heated
oxygen sensors monitor the composition of the exhaust gases leaving the engine. The exhaust gas
analysis is fed into an electronic module. This adjusts the air-fuel ratio to provide optimum conditions
for combustion and efficient reduction of the three major pollutants (hydrocarbons, carbon monoxide
and oxides of nitrogen) by a three-way catalytic converter.
Air pump system
During cold starts, an electric pump is activated which directs air to the exhaust channels. This initiates a
secondary combustion of exhaust gases which helps maximize hydrocarbon and carbon monoxide levels
and reduces warm-up time for the three-way catalytic converter. The pump begins to function when the
engine is started. It remains in operation until the three-way catalytic converter has reached normal
operating temperature. A sound may be audible from the air pump during this warm-up period. This is
normal. When idling, the air pump performs a self-diagnosis. A soft whining noise can be heard, which
is also normal.
pg. 8:11 Servicing
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