80 Technical Description
Fault criteria, front heated oxygen sensor
The oxygen sensor's ability to react quickly to
changes in the fuel-air mixture is diagnosed once
per trip.
The sensor's transition frequency is measured when
the conditions for diagnosis are fulfilled.
Transition is what happens when the sensor voltage
goes from high to low or from low to high.
If the transition frequency is too low, the sensor is de-
fective.
The number of sensor transitions taking place during
250 engine revolutions is counted.
If the number exceeds 14 the diagnosis is OK.
If the number of transitions is less than 14, two addi-
tional attempts to obtain a "diagnosis OK" result this
trip will be made.
If the sensor is failed on all three diagnostic occa-
sions the fault criteria are satisfied.
In other respects the sensor and its heating element
are monitored according to the On-Board Diagnostic
I model.
Conditions for diagnosis
• Diagnosis not yet performed this trip
• Vehicle speed
= o
• Idling speed
• Closed loop activated
• Coolant temperature above 60°C (140°F)
• Sensor heating current less than 1500 mA
• No load changes
1 2 3 4 5 6 7 8 9 10 1112 13 14 15 16
Rev -+------~-----------.----.---1-.----
0
100 200 250 300
Saab 9000
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