Saab 9000 - Page 87

84 Technical Description
Fault criteria, catalyst
The three way catalytic converter is diagnosed once
per trip.
The three way catalytic converter's ability to store
oxygen is proportional to its efficiency.
If the ability of the three way catalytic converter to
store oxygen is poor, the closed loop's natural fuel-
air ratio oscillations
will
also
be noticed after the three
way catalytic converter.
An oxygen sensor is also mounted after the three
way catalytic converter (rear heated oxygen sensor).
When the conditions for diagnosis are fulfilled, the
voltage changes emanating from the rear heated
oxygen sensor are analyzed. If the voltage changes
are excessive, having regard to engine load and spe-
ed, the three way catalytic converter is defective.
The voltage changes emanating from the rear hea-
ted oxygen sensor are corrected in regard to engine
load and speed and totalled in 50 individual, appro-
ved periods for the front heated oxygen sensor
*).
If the total exceeds a calibrated value, the fault crite-
ria are satisfied.
*)
An approved period is when the pulse ratio of the
sensor voltage is 30-80% (
+).
Conditions for diagnosis
• Diagnosis not yet performed this trip
Ox1
Cycles
Ox2
.L\mV
40
50
Heating of the three way catalytic converter:
• Vehicle speed
>
O
mph (>
O
km/h)
• Open throttle
• Engine speed (rpm) x load (kPa)
=
>
60,000
•
Aggregate acceleration
> 15
sec.
•
Above conditions fulfilled for
120
sec.
•
No idling period
>
40
sec.
• No fuel shut-of> 1
O
sec.
Evaluation
of
the
three way catalytic converter
• Speed 19-62mph (30-100km/h).
• Open throttle
• Closed loop activated
• Engine speed (rpm) x load (kPa)
=
60,000 -
260,000
• Coolant temperature
>
60°
C (> 140° F)
• Rear heated oxygen sensor
>
0.4
V at any time in
this driving cycle.
30
25
Saab 9000