P0420 Catalyst System Efficiency below Threshold (Bank 1) - Automotive Repair Guides & Equipment

COMPONENT LOCATION

GENERAL DESCRIPTION

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.

DTC DESCRIPTION

If the oxygen storage time for Bank 1 is lower than threshold, the ECM determines that a fault exists and a DTC is stored .

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.

1.	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

No instrumentation slews active

Threshold value

Oxygen Storage Time < 1.2 sec.

Diagnosis Time

15 sec.

MIL On Condition

1 Driving cycle

MONITOR GDS DATA

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

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.

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.

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.

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