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   7 

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 / Data List / 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: 

   • The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 25%.
   • 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)	+25%	Rich	Less than 3.1
     	-12.5%	Lean	More than 3.4
     O2S B1S2 (Heated Oxygen)	+25%	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 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	A
     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 Control the Injection Volume for A/F Sensor, 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   8 

C → See step   6 

A: Go to next step 

1. Check exhaust system.

   OK

   No gas leaks.

   Result	Proceed to
   OK (2WD)	A
   OK (4WD)	B
   NG	C

B → See step   5 

C → REPAIR OR REPLACE EXHAUST GAS LEAK POINT 

A: Go to next step 

1. Replace exhaust manifold converter sub-assembly. Refer to REMOVAL .

NEXT → See step   9 

1. Replace exhaust manifold converter sub-assembly. Refer to REMOVAL .

NEXT → See step   11 

1. Check exhaust system.

   OK

   No gas leaks.

NG → REPAIR OR REPLACE EXHAUST GAS LEAK POINT 

OK → See step   10