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 1 is lower than threshold , the PCM 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. | ● 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. | |
DiagnosisTime | ● 15 sec. | |
MIL On Condition | ● 1 Driving cycle |
Check DTC Status
Connect scantool to Data Link Connector(DLC).
IG "ON".
Select "Diagnostic Trouble Codes(DTCs)" mode, and then Press F4(DTAL) to check DTC's information from the DTCs menu
Read "DTC Status" parameter.
Is parameter displayed "Present fault"?
▶ Substitute with a known - good Catalyst Converter and check for proper operation. If the problem is corrected, Go to "Verification of Vehicle Repair" procedure.
▶ Go to "Component Inspection" procedure.
Monitor the Catalyst Converter
IG "OFF" and then reset the PCM.
Start the engine and warm it up until the radiator fan comes on( more than at least 10 minutes).
Drive at a steady speed between 45-55 mph(72-88 km/h) for 30 seconds.
Stop and then maintain idle state for 30 seconds in D-position.
Repeat step 3 once again.
Stop and then keep it in idle state( D-positon) for 30 seconds.
IG "OFF"
Repeat steps 3 through 7 three times.
Check if catalyst monitoring readiness is complete. so, if the readiness is incomplete, repeat steps 2 through 8.
Does the scan tool show DTC P0420?
▶ Substitute with a known - good Catalyst Converter and check the signal waveform of HO2S for proper operation. If the problem is corrected, Go to "Verification of Vehicle Repair" procedure.
▶ It was intermittent failure.
After a repair, it is essential to verify that the fault has been corrected.
Monitor and record the Freeze Frame Data for the Diagnostic Trouble Code(DTC) which has been diagnosed.
Using a Scantool, Clear the DTCs
Operate the vehicle within conditions noted in the freeze frame data or enable conditions
Monitor that all rediness test have been verified as " Complete "
Are any DTCs present ?
▶ Go to the applicable troubleshoooting procedure.
▶ System is performing to specification at this time.
