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.
6. Perform the Active Test operation with the engine in an idling condition (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 B1S1AFS 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 (A/F)	+12%	Rich	Less than 3.1
   	-12%	Lean	More than 3.4
   O2S B1S2 (HO2)	+12%	Rich	More than 0.55
   	-12%	Lean	Less than 0.4

   RESULT
   
   

   Status AFS Voltage B1S1	Status O2S B1S2	A/F Condition and A/F and HO2 Sensor Condition	Misfire	Main Suspected Trouble Area	Proceed to
   Lean/Rich	Lean/Rich	Normal	-	Three-Way Catalytic Converter 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
   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
   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, the A/F sensor output voltage (AFS Voltage B1S1) is consistently more than 3.4 V, and the HO2 sensor output voltage (O2S B1S2) is consistently less than 0.4 V.

   Rich: During Control the Injection Volume, 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 of the Active Test, the output voltage of the HO2 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 to ON.
6. Turn the Techstream on.
7. Start the engine.
8. Drive the vehicle in accordance with the driving pattern described in Confirmation Driving Pattern.
9. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
10. 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