DTC P0420: Catalyst System Efficiency Below Threshold (Bank 1); DTC P0430: Catalyst System Efficiency Below Threshold (Bank 2): Procedure

1. Connect Techstream to the DLC3.
2. Turn the ignition switch to ON and turn the Techstream on.
3. Enter the following menus: Powertrain / Engine / Trouble Codes.
4. Read the DTCs.

   Result

   Display (DTC output)	Proceed to
   P0420 and/or P0430	A
   P0420 and/or P0430 and other DTCs	B

   HINT: 

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

B → See step   9 

A: Go to next step 

1. Connect Techstream to the DLC3.
2. Start the engine and turn the Techstream on.
3. Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.
4. On the Techstream, enter the following menus: Powertrain / Engine / Active Test / Control the Injection Volume for A/F Sensor.
5. Perform the A/F CONTROL operation with the engine in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume).
6. Monitor the output voltages of the A/F and HO2 sensors (AFS Voltage B1 S1 and O2S B1 S2 or AFS Voltage B2 S1 and O2S B2 S2) displayed on the Techstream.

   HINT: 

   • The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 25%.
   • Each sensor reacts in accordance with increases and decreases in the fuel injection volume.

   Techstream Display (Sensor)	Injection Volume	Status	Voltage
   AFS Voltage B1 S1 or AFS Voltage B2 S1 (A/F)	+25%	Rich	Less than 3.1 V
   AFS Voltage B1 S1 or AFS Voltage B2 S1 (A/F)	-12.5%	Lean	More than 3.4 V
   O2S B1 S2 or O2S B2 S2 (HO2)	+25%	Rich	More than 0.55 V
   O2S B1 S2 or O2S B2 S2 (HO2)	-12.5%	Lean	Less than 0.4 V

   Result

   Status AFS Voltage B1 S1 or AFS Voltage B2 S1	Status O2S B1 S2 or O2S B2 S2	A/F Condition and A/F and HO2 Sensor Conditions	Misfire	Main Suspected Trouble Areas	Proceed to
   Lean/Rich	Lean/Rich	Normal	-	Three-Way Catalytic Converter (TWC) Gas leakage from exhaust system	A
   Lean	Lean/Rich	A/F sensor malfunction	-	A/F sensor	B
   Rich	Lean/Rich	A/F sensor malfunction	May occur	A/F sensor	B
   Lean/Rich	Lean	HO2 sensor malfunction	-	HO2 sensor Gas leakage from exhaust system	C
   Lean/Rich	Rich	HO2 sensor malfunction	-	HO2 sensor Gas leakage from exhaust system	C
   Lean	Lean	Actual air-fuel ratio lean	May occur	Extremely rich or lean actual air-fuel ratio Gas leakage from exhaust system	D
   Rich	Rich	Actual air-fuel ratio lean	-	Extremely rich or lean actual air-fuel ratio Gas leakage from exhaust system	D

   • Lean:
     • During Control the Injection Volume for A/F Sensor, the A/F sensor (AFS) output voltage is consistently more than 3.4 V, and the HO2 sensor output voltage (O2S) is consistently less than 0.4 V.
   • Rich:
     • During Control the Injection Volume for A/F Sensor, the AFS is consistently less than 3.1 V, and the O2S is consistently more than 0.55 V.
   • Lean/Rich:
     • During Control the Injection Volume for A/F Sensor of the Active Test, the output voltage of the HO2 sensor alternates correctly.

D → See step   8 

C → See step   7 

B → CHECK AND REPLACE AIR FUEL RATIO SENSOR 

A: Go to next step 

OK

No gas leakage.

NG → REPAIR OR REPLACE EXHAUST GAS LEAKAGE POINT 

OK: Go to next step 

1. Connect Techstream to the DLC3.
2. Turn the ignition switch to ON and turn the Techstream on.
3. Enter the following menus: Powertrain / Engine / Trouble Code.
4. Read the DTCs.

   Result

   Display (DTC output)	Proceed to
   P0420	A
   P0430	B
   P0420 and P0430	A and B

B → See step   6 

A → See step   5 

1. Replace the exhaust manifold sub-assembly RH.

NEXT → REPLACE FRONT EXHAUST PIPE ASSEMBLY 

1. Replace the exhaust manifold sub-assembly LH.

NEXT → REPLACE FRONT EXHAUST PIPE ASSEMBLY 

OK

No gas leakage.

NG → REPAIR OR REPLACE EXHAUST GAS LEAKAGE POINT 

OK → REPLACE HEATED OXYGEN SENSOR 

OK

No gas leakage.

NG → REPAIR OR REPLACE EXHAUST GAS LEAKAGE POINT 

OK → CHECK ENGINE TO DETERMINE CAUSE OF EXTREMELY RICH OR LEARN ACTUAL AIR FUEL RATIO