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
   DTC P0420 is output	A
   DTC P0420 and other DTCs are output	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 for A/F Sensor.
6. Change the fuel injection volume using the Techstream and monitor the voltage output of the air fuel ratio and heated oxygen sensors displayed on the Techstream.

   HINT: 

   • The Control the Injection Volume for A/F Sensor operation lowers or increases the fuel injection volume by 12.5%.
   • The air fuel ratio sensor is displayed as AFS Voltage B1S1, and the heated oxygen sensor is displayed as O2S B1S2, on the Techstream.
   • 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)	12.5%	Rich	Less than 3.1
   	-12.5%	Lean	More than 3.4
   O2S B1S2 (Heated oxygen)	12.5%	Rich	More than 0.55
   	-12.5%	Lean	Less than 0.4

   RESULT
   
   

   Status AFS Voltage B1S1	Status O2S B1S2	Air Fuel Ratio Condition and Air Fuel Ratio and Heated Oxygen Sensor Condition	Misfire	Main Suspected Trouble Area	Proceed to
   Lean/Rich	Lean/Rich	Normal	-	Three-Way Catalytic Converter (TWC) Gas leakage 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 leakage from exhaust system	C
   Lean/Rich	Rich	Heated oxygen sensor malfunction	-	Heated oxygen sensor Gas leakage from exhaust system
   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

   Lean: During Control the Injection Volume for A/F Sensor, the air fuel ratio sensor output voltage (AFS Voltage B1S1) is consistently more than 3.4 V, and the heated oxygen sensor output voltage (O2S B1S2) is consistently less than 0.4 V.

   Rich: During Control the Injection Volume for A/F Sensor, the AFS Voltage B1S1 is consistently less than 3.1 V, and the O2S B1S2 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 air fuel ratio sensor and heated oxygen sensor alternates correctly.

B → See step   5 

C → See step   6 

D → See step   8 

A: Go to next step 

1. Check for exhaust gas leak.

   OK

   No gas leak.

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 front exhaust pipe assembly (TWC: Front catalyst and rear catalyst). Refer to REMOVAL .

NEXT → END 

1. Replace the air fuel ratio sensor (sensor 1). Refer to REMOVAL .

NEXT → See step   11 

1. Check for exhaust gas leak.

   OK

   No gas leak.

NG → See step   10 

OK: Go to next step 

1. Replace the heated oxygen sensor (sensor 2). Refer to REMOVAL .

NEXT → See step   11 

1. Check for exhaust gas leak.

   OK

   No gas leak.

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 INSPECTION PROCEDURE .

NEXT → See step   11 

1. Repair or replace exhaust gas leak point. Refer to COMPONENTS .

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 pending DTCs.
    RESULT
    
    

    Result	Proceed to
    DTC P0420 is output	A
    DTC is not 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 front exhaust pipe assembly (TWC: Front catalyst and rear catalyst). Refer to COMPONENTS .

NEXT → END