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 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 is working properly, it used oxygen in the exhaust. The oxygen levels coming out of the catalyst should be lower and a more stable level. This would produce a somewhat level HO2S reading around 700 to 800 mv. 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 of the catalyst. This will give a HO2S reading simular to the upstream sensor.
If the oxygen storage time for Bank 1 is lower than threshold , the ECM determines that a fault exists and a DTC is stored .
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. |
•
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 < 1.2 sec. | |
Diagnosis Time |
•
15 sec. | |
MIL On Condition |
•
1 Driving cycle |
