Fuel System > Engine Control System > P0420 Catalyst System Efficiency below Threshold (Bank 1)

General Description

The PCM 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.

DTC Description

If the oxygen storage time for Bank 1 is lower than threshold , the PCM determines that a fault exists and a DTC is stored. MIL(Malfunction Indication Lamp) turns on.

DTC Detecting Condition

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°C(158 °F) ≤ Coolant Temp. ≤ 120°C(248 °F)

•	-7°C(19.4 °F) ≤ Ambient Temp. ≤ 105°C(221 °F)

•	Barometer ≥ 72 kPa

•	Max number of test attempts ≤ 12

•	Closed Loop

•	250°C( 482 °F) ≤ Catalyst Temp. ≤ 950°C(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

Threshold value

•	Oxygen Storage Time < 3.25 sec.

DiagnosisTime

•

15 sec.

MIL On Condition

•	1 Driving cycle

Monitor Scantool Data

Check DTC Status

(1)	Connect scantool to Data Link Connector(DLC).

(2)

IG "ON".

(3)	Select "DTC" button, and then Press "DTC Status" to check DTC's information from the DTCs menu.

(4)	Read "DTC Status" parameter.

(5)

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.

Component Inspection

Monitor the Catalyst Converter

(1)	Clear DTC.

(2)	Start the engine and warm it up until the radiator fan comes on( more than at least 10 minutes).

(3)	Drive at a steady speed between 45-55 mph(72-88 km/h) for 30 seconds.

(4)	Stop and then maintain idle state for 120 seconds in D-position.

(5)	Repeat step 3 once again.

(6)	Stop and then keep it in idle state( D-positon) for 120 seconds.

(7)	Repeat step 3 once again.

(8)	Stop and then maintain idle state for 120 seconds in D-position.

(9)

IG "OFF"

(10)	Repeat steps 3 through 9 three times.

(11)	Check if catalyst monitoring readiness is complete. so, if the readiness is incomplete, repeat steps 2 through 10.

(12)

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.

Verification Of Vehicle Repair

After a repair, it is essential to verify that the fault has been corrected.

1.	Connect scantool and select "DTC" button.

2.	Press "DTC Status" button and confirm that "DTC Readiness Flag" indicates "Completed". If not, drive the vehicle within conditions noted in the freeze frame data or enable conditions

3.	Read "DTC Status" parameter

Is parameter displayed "History(Not Present) fault"?

	▶ System performing to specification at this time. Clear the DTC
	▶ Go to the applicable troubleshooting procedure.