Fuel injection ·{contd.)
Rear heated oxygen sensor (after three way ca-
talytic converter)
An oxygen sensor is mounted in the exhaust system
after the three way catalytic converter for the pur-
pose of diagnosing it.
The oxygen sensor is connected to pin 70 of the elec-
tronic control module and grounded via pin 47.
The sensor heating element is supplied with current
(B+ circuit) from the fuel pump relay via fuse 28 and
grounded via pin
51
of
the engine control module.
The control module cuts off the current to the heating
element when the engine coolant temperature drops
below 50°C
(122°F)
and
when the estimated exhaust
temperature is high.
To improve exhaust emissions still further, the value
from the sensor is used to correct the closed loop.
The most favourable emission values are obtained
when the oxygen sensor voltage is 0.6 V.
If sensor voltage is 0.3 V, for instance, the engine is
running on a slightly lean mixture. The closed loop
will then be corrected so that the fuel-air mixture is
Technical Description 49
µp
µp
kept rich for a longer time than it is kept lean, thus in-
creasing the sensor voltage.
Important
The oxygen sensor obtains reference oxygen from
the ambient air via the connecting cables. For this
reason, contact cleaner or grease must
not
be
used on the oxygen sensor connector.
Saab 9000
I
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