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

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

   Result

   Result	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   13 

A: Go to next step 

1. Connect the Techstream to the DLC3.
2. Start the engine and warm it up.
3. Turn the Techstream on.
4. Run the engine at an engine speed of 2500 rpm for approximately 90 seconds.
5. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume / GAS AF Control / AFS Voltage B1S1 and O2S B1S2.
6. Perform the Active Test operation with the engine idling (press the RIGHT or LEFT button to change the fuel injection volume).
7. Monitor the voltage outputs of the air fuel ratio sensor and heated oxygen sensor (AFS Voltage B1S1 and O2S B1S2) displayed on the Techstream.

   HINT: 

   • Change the fuel injection volume within the range of - 12% to +12%. The injection volume can be changed in fine gradations.
   • Each sensor reacts in accordance with increases and decreases in the fuel injection volume.
   • 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.
   • If the sensor output voltage does not change (almost no reaction) while performing the Active Test, the sensor may be malfunctioning.

   Standard

   Techstream Display (Sensor)	Injection Volume	Status	Voltage
   AFS Voltage B1S1 (Air fuel ratio)	+12%	Rich	Below 3.1 V
   	-12%	Lean	Higher than 3.4 V
   O2S B1S2 (Heated oxygen)	+12%	Rich	Higher than 0.55 V
   	-12%	Lean	Below 0.4 V

   RESULT
   
   

   Status AFS Voltage B1S1	Status O2S B1S2	Actual air fuel ratio, air fuel ratio sensor and heated oxygen sensor condition	Misfire	Main Suspected Trouble Area	Proceed to
   Lean/Rich	Lean/Rich	Normal	-	Three-way catalytic converter Gas leak 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
   Lean/Rich	Lean	Heated oxygen sensor malfunction	-	Heated oxygen sensor Gas leak from exhaust system	C
   Lean/Rich	Rich	Heated oxygen sensor malfunction	-	Heated oxygen sensor Gas leak from exhaust system
   Lean	Lean	Actual air fuel ratio lean	May occur	Extremely lean actual air fuel ratio Gas leak from exhaust system	D
   Rich	Rich	Actual air fuel ratio rich	-	Extremely rich actual air fuel ratio Gas leak from exhaust system

   • Lean: During Control the Injection Volume, the air fuel ratio sensor output voltage (AFS Voltage B1S1) is consistently higher than 3.4 V, and the heated oxygen sensor output voltage (O2S B1S2) is consistently below 0.4 V.
   • Rich: During Control the Injection Volume, the AFS Voltage B1S1 is consistently below 3.1 V, and the O2S B1S2 is consistently higher than 0.55 V.
   • Lean/Rich: During Control the Injection Volume of the Active Test, the output voltage of the air fuel ratio sensor and heated oxygen sensor alternate correctly.

B → See step   5 

C → See step   6 

D → See step   8 

A: Go to next step 

1. Check for exhaust gas leaks.

   OK

   No gas leaks.

NG → See step   10 

OK: Go to next step 

HINT: 

Confirm the replacement parts, referring to the illustration in the Catalyst Location.

1. Replace the exhaust manifold converter sub-assembly (TWC: Front catalyst). Refer to COMPONENTS .
2. Replace the center exhaust pipe assembly (TWC: Rear catalyst). Refer to COMPONENTS for 2WD. Refer to COMPONENTS for 4WD).

NEXT → END 

1. Replace the air fuel ratio sensor. Refer to COMPONENTS .

NEXT → See step   11 

1. Check for exhaust gas leaks.

   OK

   No gas leaks.

NG → See step   10 

OK: Go to next step 

1. Replace the heated oxygen sensor. Refer to COMPONENTS .

NEXT → See step   11 

1. Check for exhaust gas leaks.

   OK

   No gas leaks.

NG → See step   10 

OK: Go to next step 

1. Check the cause of extremely rich or lean actual air fuel ratio, referring to the DTC P0171 Inspection Procedure. Refer to DTC P0171: System Too Lean (Bank 1); DTC P0172: System Too Rich (Bank 1) .

NEXT → See step   11 

1. Repair or replace exhaust gas leak point.

NEXT: Go to next step 

1. Connect the Techstream to the DLC3.
2. Turn the ignition switch to ON.
3. Turn the Techstream on.
4. Clear the DTCs. Refer to DTC CHECK / CLEAR .
5. Turn the ignition switch off and wait for at least 30 seconds.
6. Turn the ignition switch to ON.
7. Turn the Techstream on.
8. Start the engine.
9. Drive the vehicle in accordance with the driving pattern described in Confirmation Driving Pattern.
10. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
11. Read the DTCs.
    RESULT
    
    

    Result	Proceed to
    DTC P0420 is output	A
    DTC is not output (No pending DTCs output)	B

B → END 

A: Go to next step 

HINT: 

Confirm the replacement parts, referring to the illustration in the Catalyst Location.

1. Replace the exhaust manifold converter sub-assembly (TWC: Front catalyst). Refer to COMPONENTS .
2. Replace the center exhaust pipe assembly (TWC: Rear catalyst). Refer to COMPONENTS for 2WD. Refer to COMPONENTS for 4WD).

NEXT → END