SFI SYSTEM, Diagnostic DTC:P0420, P0430

DTC Code	DTC Name
P0420	Catalyst System Efficiency Below Threshold (Bank 1)
P0430	Catalyst System Efficiency Below Threshold (Bank 2)

DESCRIPTION

The ECM uses the sensors mounted in front of and behind the three-way catalytic converter to monitor its efficiency.

The first sensor, the air fuel ratio sensor, sends pre-catalyst information to the ECM. The second sensor, the heated oxygen sensor, sends post-catalyst information to the ECM.

In order to detect any deterioration in the three-way catalytic converter, the ECM calculates the oxygen storage capacity of the three-way catalytic converter. This calculation is based on the voltage output of the heated oxygen sensor while performing active air fuel ratio control, rather than the conventional detecting method, which uses the locus ratio.

The oxygen storage capacity value is an indication of the oxygen storage capacity of the three-way catalytic converter. When the vehicle is being driven with a warm engine, active air fuel ratio control is performed for approximately 15 to 20 seconds. When it is performed, the ECM deliberately sets the air fuel ratio to lean or rich levels. If the rich-lean cycle of the heated oxygen sensor is long, the oxygen storage capacity is large. There is a direct correlation between the oxygen storage capacities of the three-way catalytic converter and the response of the heated oxygen sensor.

The ECM uses the oxygen storage capacity value to determine the state of the three-way catalytic converter. If any deterioration has occurred, the ECM illuminates the MIL and sets a DTC.

DTC No.	DTC Detection Condition	Trouble Area
P0420	Oxygen storage capacity value smaller than standard value under active air fuel ratio control (2 trip detection logic)	Gas leaks from exhaust system Air fuel ratio sensor (bank 1 sensor 1) Heated oxygen sensor (bank 1 sensor 2) Exhaust manifold sub-assembly RH (three-way catalytic converter) Front exhaust pipe assembly
P0430	Oxygen storage capacity value smaller than standard value under active air fuel ratio control (2 trip detection logic)	Gas leaks from exhaust system Air fuel ratio sensor (bank 2 sensor 1) Heated oxygen sensor (bank 2 sensor 2) Exhaust manifold sub-assembly LH (three-way catalytic converter) Front exhaust pipe assembly

Bank 1 refers to the bank that includes cylinder No. 1.
Bank 2 refers to the bank that does not include cylinder No. 1.
Sensor 1 refers to the sensor closest to the engine assembly.
Sensor 2 refers to the sensor farthest away from the engine assembly.

CONDITIONING FOR SENSOR TESTING

Tech Tips

Perform the operation with the engine speeds and time durations described below prior to checking the waveforms of the air fuel ratio and heated oxygen sensors. This is in order to activate the sensors sufficiently to obtain the appropriate inspection results.

Connect the intelligent tester to the DLC3 (Procedure "A").
Start the engine and warm it up with all the accessories switched off, until the engine coolant temperature stabilizes (Procedure "B").
Run the engine at an engine speed of between 2500 rpm and 3000 rpm for at least 3 minutes (Procedure "C").
While running the engine at 3000 rpm and 2000 rpm for 2 seconds, check the waveforms of the air fuel ratio and heated oxygen sensors using the tester (Procedure "D").
Tech Tips
- If either of the voltage outputs of the air fuel ratio or heated oxygen sensor does not fluctuate, or either of the sensors makes a noise, the sensor may be malfunctioning.
- If the voltage outputs of both the sensors remain lean or rich, the air fuel ratio may be extremely lean or rich. In such cases, enter the following menus: Powertrain / Engine / Active Test / Control the Injection Volume for A/F Sensor.
- If the three-way catalytic converter has deteriorated, the heated oxygen sensor (located behind the three-way catalytic converter) voltage output fluctuates up and down frequently, even under normal driving conditions (active air fuel ratio control is not performed).

INSPECTION PROCEDURE

Tech Tips

Intelligent tester only:

Malfunctioning areas can be identified by performing the Control the Injection Volume for A/F Sensor function provided in the Active Test. The Control the Injection Volume for A/F Sensor function can help to determine whether the air fuel ratio sensor, heated oxygen sensor and other potential trouble areas are malfunctioning.

The following instructions describe how to conduct the Control the Injection Volume for A/F Sensor operation using the intelligent tester.

Start the engine and turn the tester on.
Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.
Enter the following menus: Powertrain / Engine / Active Test / Control the Injection Volume for A/F Sensor.
Perform the Active Test operation with the engine in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume).

Monitor the voltage outputs of the air fuel ratio and heated oxygen sensors (AFS Voltage B1S1 and O2S B1S2 or AFS Voltage B2S1 and O2S B2S2) displayed on the tester.

Tech Tips

The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 12.5%.
Each sensor reacts in accordance with increases and decreases in the fuel injection volume.

Tester Display (Sensor)	Injection Volume	Status	Voltage
AFS Voltage B1S1 or AFS Voltage B2S1 (Air fuel ratio)	12.5%	Rich	Less than 3.1
AFS Voltage B1S1 or AFS Voltage B2S1 (Air fuel ratio)	-12.5%	Lean	More than 3.4
O2S B1S2 or O2S B2S2 (Heated oxygen)	12.5%	Rich	More than 0.55
O2S B1S2 or O2S B2S2 (Heated oxygen)	-12.5%	Lean	Less than 0.4

Note

The air fuel ratio sensor has an output delay of a few seconds and the heated oxygen sensor has a maximum output delay of approximately 20 seconds.

Case	Air Fuel Ratio Sensor (Sensor 1) Output Voltage	Heated Oxygen Sensor (Sensor 2) Output Voltage	Main Suspected Trouble Area
1			-
2			Air fuel ratio sensor Air fuel ratio sensor heater Air fuel ratio sensor circuit
3			Heated oxygen sensor Heated oxygen sensor heater Heated oxygen sensor circuit Exhaust gas leaks
4			Fuel pressure Exhaust gas leaks (Air fuel ratio extremely lean or rich)

Connect the intelligent tester to the DLC3.
Following the Control the Injection Volume for A/F Sensor procedure enables technicians to check and graph the voltage outputs of both the air fuel ratio and heated oxygen sensors.
To display the graph, enter the following menus: Powertrain / Engine / Active Test / Control the Injection Volume for A/F Sensor / A/F Control System / AFS Voltage B1S1 and O2S B1S2 or AFS Voltage B2S1 and O2S B2S2.

Tech Tips

Read freeze frame data using the intelligent tester. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.

PROCEDURE

CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0420 AND/OR P0430)

Connect the intelligent tester to the DLC3.
Turn the engine switch on (IG) and turn the tester on.
Enter the following menus: Powertrain / Engine / DTC.

Read the DTCs.

Result

Result	Proceed to
DTC P0420 and/or P0430 are output	A
DTC P0420 and/or P0430 and other DTCs are output	B

Tech Tips

If any DTCs other than P0420 or P0430 are output, troubleshoot those DTCs first.

GO TO DTC CHART Click here

PERFORM ACTIVE TEST USING INTELLIGENT TESTER (AIR FUEL RATIO CONTROL)

Connect the intelligent tester to the DLC3.
Start the engine and turn the tester on.
Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.
Enter the following menus: Powertrain / Engine / Active Test / Control the Injection Volume for A/F Sensor.
Perform the Control the Injection Volume for A/F Sensor operation with the engine in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume).

Monitor the voltage outputs of the air fuel ratio and heated oxygen sensors (AFS Voltage B1S1 and O2S B1S2 or AFS Voltage B2S1 and O2S B2S2) displayed on the tester.

Tech Tips

The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 12.5%.
Each sensor reacts in accordance with increases and decreases in the fuel injection volume.

Tester Display (Sensor)	Injection Volume	Status	Voltage
AFS Voltage B1S1 or AFS Voltage B2S1 (Air fuel ratio)	12.5%	Rich	Less than 3.0 V
AFS Voltage B1S1 or AFS Voltage B2S1 (Air fuel ratio)	-12.5%	Lean	More than 3.35 V
O2S B1S2 or O2S B2S2 (Heated oxygen)	12.5%	Rich	More than 0.55 V
O2S B1S2 or O2S B2S2 (Heated oxygen)	-12.5%	Lean	Less than 0.4 V

Result

Status AFS Voltage B1S1 or AFS Voltage B2S1	Status O2S B1S2 or O2S B2S2	Air Fuel Ratio Condition and Air Fuel Ratio and Heated Oxygen Sensor Condition	Misfire	Suspected Trouble Area	Proceed to
Lean/Rich	Lean/Rich	Normal	-	Three-way catalytic converter Gas leaks from exhaust system	A
Lean	Lean/Rich	Air fuel ratio sensor malfunction	-	Air fuel ratio sensor	B
Rich	Lean/Rich	Air fuel ratio sensor malfunction	-	Air fuel ratio sensor	B
Lean/Rich	Lean	Heated oxygen sensor malfunction	-	Heated oxygen sensor Gas leaks from exhaust system	C
Lean/Rich	Rich	Heated oxygen sensor malfunction	-	Heated oxygen sensor Gas leaks from exhaust system	C
Lean	Lean	Actual air fuel ratio lean	May occur	Extremely rich or lean actual air fuel ratio Gas leaks from exhaust system	A
Rich	Rich	Actual air fuel ratio rich	-	Extremely rich or lean actual air fuel ratio Gas leaks from exhaust system	A

Lean: During the Control the Injection Volume for A/F Sensor Active Test, the air fuel ratio sensor output voltage (AFS) is consistently more than 3.35 V, and the heated oxygen sensor output voltage (O2S) is consistently less than 0.4 V.

Rich: During the Control the Injection Volume for A/F Sensor Active Test, the AFS is consistently less than 3.0 V, and the O2S is consistently more than 0.55 V.

Lean/Rich: During the Control the Injection Volume for A/F Sensor Active Test, the output voltage of the heated oxygen sensor alternates correctly.

REPLACE AIR FUEL RATIO SENSOR Click here

INSPECT FOR EXHAUST GAS LEAK Click here

INSPECT FOR EXHAUST GAS LEAK
1. Inspect for exhaust gas leak from the exhaust manifold sub-assembly and exhaust pipe.
  
  OK
  
  No gas leaks.
NG
REPAIR OR REPLACE EXHAUST GAS LEAK POINT

OK

OK
No gas leaks.

CHECK DTC OUTPUT (DTC P0420 AND/OR P0430)

Connect the intelligent tester to the DLC3.
Turn the engine switch on (IG).
Turn the tester on.
Enter the following menus: Powertrain / Engine / DTC.

Read the DTCs.

Result

Result	Proceed to
DTC P0420 is output	A
DTC P0430 is output	B
DTCs P0420 and P0430 are output	A and B

REPLACE EXHAUST MANIFOLD SUB-ASSEMBLY LH Click here

REPLACE EXHAUST MANIFOLD SUB-ASSEMBLY RH
1. Replace the exhaust manifold sub-assembly RH Click here.
NEXT

REPLACE FRONT EXHAUST PIPE ASSEMBLY Click here
REPLACE EXHAUST MANIFOLD SUB-ASSEMBLY LH
1. Replace the exhaust manifold sub-assembly LH Click here.
NEXT

REPLACE FRONT EXHAUST PIPE ASSEMBLY Click here
INSPECT FOR EXHAUST GAS LEAK
1. Inspect for exhaust gas leak from the exhaust manifold sub-assembly and exhaust pipe.
  
  OK
  
  No gas leaks.
NG
REPAIR OR REPLACE EXHAUST GAS LEAK POINT

OK

REPLACE HEATED OXYGEN SENSOR Click here