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

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

   Result

   Display (DTC Output)	Proceed to
   P0420	A
   P0420 and other DTCs	B

   HINT: 

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

B → See step   6 

A: Go to next step 

1. Connect the Techstream to the DLC3.
2. Start the engine and turn the Techstream on.
3. Warm up the engine at an engine speed of 2,500 RPM for approximately 90 seconds.
4. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.
5. 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).
6. Monitor the voltage outputs of the A/F and HO2 sensors (AFS Voltage B1S1 and O2S B1S2) 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.

   Standard voltage

   Techstream Display (Sensor)	Injection Volume	Status	Voltage
   AFS Voltage B1S1 (A/F)	+25%	Rich	Less than 3.1 V
   AFS Voltage B1S1 (A/F)	-12.5%	Lean	More than 3.4 V
   O2S B1S2 (HO2)	+25%	Rich	More than 0.55 V
   O2S B1S2 (HO2)	-12.5%	Lean	Less than 0.4 V

   Result

   Status AFS Voltage B1S1	Status O2S B1S2	A/F Condition and A/F Sensor Condition	Misfire	Suspected Trouble Area	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	-	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 rich	-	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 output voltage (AFS) 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 → GO TO NEXT STEP AFTER CHECKING ENGINE TO DETERMINE CAUSE OF EXTREMELY RICH OR LEAN ACTUAL AIR FUEL RATIO 

C → See step   5 

B → CHECK AND REPLACE AIR FUEL RATIO SENSOR 

A: Go to next step 

1. Inspect for exhaust gas leaks.

   OK

   No gas leakage.

NG → REPAIR OR REPLACE EXHAUST GAS LEAK POINT 

OK: Go to next step 

1. Replace exhaust manifold converter sub-assembly. Refer to REMOVAL - Step 30 .

NEXT → See step   7 

1. Inspect for exhaust gas leaks.

   OK

   No gas leaks.

NG → REPAIR OR REPLACE EXHAUST GAS LEAK POINT 

OK → See step   8