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 the 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 / All Data / AFS Voltage B1S1 and O2S B1S2.
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 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 there is almost no response from the air fuel ratio sensor, a malfunction of the air fuel ratio sensor is suspected.

     Standard

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

     Result

     Status AFS Voltage B1S1	Status O2S B1S2	Air Fuel Ratio Condition and Air Fuel Ratio and Heated Oxygen Sensors 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	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) is consistently more than 3.4 V, and the heated oxygen sensor output voltage (O2S) is consistently less than 0.4 V.

     Rich: During the AFS Voltage 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 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 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 front exhaust pipe assembly (TWC: Front and rear catalyst). Refer to COMPONENTS .

NEXT → END 

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

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 REMOVAL .

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 case 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.

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. Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.
7. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
8. Read the DTCs.
   RESULT
   
   

   Result	Proceed to
   DTC P0420 is output	A
   DTC is not output (Pending 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 and rear catalyst). Refer to COMPONENTS .

NEXT → END