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

1. Connect the Techstream to the DLC3.
2. Turn the power switch on (IG).
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. Turn the power switch on (IG).
3. Turn the Techstream on.
4. Put the engine in inspection mode (maintenance mode). Refer to INSPECTION MODE PROCEDURE .
5. Start the engine warm it up.
6. Run up the engine at an engine speed of 2500 rpm for approximately 90 seconds.

   HINT: 

   During charging control, the engine speed is set at idle. Therefore, the engine speed does not increase when depressing the accelerator pedal. In this case, warm up the engine after charging control has completed.

7. Enter the following menus: Powertrain/Engine and ECT/Active Test/Control the Injection Volume/Data List/AFS Voltage B1S1 and O2S B1S2.
8. Perform the Active Test operation with the engine idling (press the RIGHT or LEFT button to change the fuel injection volume).
9. Monitor the output voltages 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.

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

   RESULT
   
   

   Status of AFS Voltage B1S1	Status of O2S B1S2	Air Fuel Ratio Condition and Air Fuel Ratio and Heated Oxygen Sensor Condition	Misfire	Suspected Trouble Area	Proceed to
   Lean/Rich	Lean/Rich	Normal	-	Tree-way catalytic converter Gas leaks 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	B
   Lean/Rich	Lean	Heated oxygen sensor malfunction	-	Heated oxygen sensor Gas leaks from exhaust system	C
   Lean/Rich	Rich	Heated oxygen sensor malfunction	-	Heated oxygen sensor Gas leaks from exhaust system	C
   Lean	Lean	Actual air fuel ratio lean	May occur	Extremely rich or lean actual air fuel ratio Gas leaks from exhaust system	D
   Rich	Rich	Actual air fuel ratio rich	-	Extremely rich or lean actual air fuel ratio Gas leaks from exhaust system	D

   • Lean: During the Control the Injection Volume Active Test, the air fuel ratio sensor output voltage (AFS Voltage) is consistently higher than 3.4 V, and the heated oxygen sensor output voltage (O2S) is consistently below 0.4 V.
   • Rich: During the Control the Injection Volume Active Test, the AFS Voltage is consistently below 3.1 V, and the O2S is consistently higher than 0.55 V.
   • Lean/Rich: During the Control the Injection Volume 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 exhaust manifold converter sub-assembly (TWC: Front catalyst). Refer to COMPONENTS .
2. Replace the center exhaust pipe assembly (TWC: 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 power switch on (IG).
3. Turn the Techstream on.
4. Clear the DTCs. Refer to DTC CHECK/CLEAR .
5. Turn the power switch off and wait for at least 30 seconds.
6. Drive the vehicle in accordance with the driving pattern described in 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 (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 .

NEXT → END