The ECM uses dual oxygen sensors to monitor the efficiency of the manifold catalytic converter (warm-up catalytic converter). By monitoring the oxygen storage capacity of a catalyst, its efficiency can be indirectly calculated. The upstream (front) HO2S is used to detect the amount of oxygen in the exhaust gas before it enters the catalytic converter. A low voltage indicates high oxygen contents (lean air mixture). A high voltage indicates low oxygen contents (rich air mixture). When the catalyst efficiency drops, no chemical reaction takes place. This means the concentration of oxygen will be the same at the rear as it is at the front.
If the oxygen storage time for Bank 2 is lower than threshold, the ECM determines that a fault exists and a DTC is stored and MIL(Malfunction Indication Lamp) turns on.
Item | Detecting Condition | Possible cause |
DTC Strategy |
•
Manipulates Airfuel and stores the times it takes for the pre and post converter oxygen sensors to switch. | 1. Catalyst Converter |
EnableConditions |
•
Engine Runtime ≥ 580 sec.
•
Purge Concentration Learned
•
3 g/s ≤ Airflow ≤ 10 g/s
•
Throttle closed ≤ 1.5%
•
70℃(158 °F) ≤ Coolant Temp. ≤ 120℃(248 °F)
•
-7℃(19.4 °F) ≤ Ambient Temp. ≤ 105℃(221 °F)
•
Barometer ≥ 72 kPa
•
Max number of test attempts ≤ 12
•
Closed Loop
•
250℃( 482 °F) ≤ Catalyst Temp. ≤ 950℃(1742 °F)
•
Fuel learning completed
•
Vehicle speed ≤ 3 kph(1.8 mph)
•
Not airfuel ramping
•
Max idle time( about 60 sec.) not exceeded
•
No disabling faults present
•
No instrumentation slews active | |
Threshold value |
•
Oxygen Storage Time < 3.25 sec. | |
Diagnosis Time |
•
15 sec. | |
MIL On Condition |
•
1 Driving cycle |
