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   17 

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 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 for A/F Sensor / Data List / Gas AF Control / 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: 

   • The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by -12.5% or increases the injection volume by 12.5%.
   • 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)	12.5%	Rich	Below 3.1 V
   AFS Voltage B1S1 (Air fuel ratio)	-12.5%	Lean	Higher than 3.4 V
   O2S B1S2 (Heated oxygen)	12.5%	Rich	Higher than 0.55 V
   O2S B1S2 (Heated oxygen)	-12.5%	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 EGR valve assembly	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 lean actual air fuel ratio Gas leaks from exhaust system EGR valve assembly	D
   Rich	Rich	Actual air fuel ratio rich	-	Extremely rich actual air fuel ratio Gas leaks from exhaust system EGR valve assembly	D

   Lean: During the Control the Injection Volume for A/F Sensor 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 for A/F Sensor 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 for A/F Sensor Active Test, the output voltage of the air fuel ratio sensor and the heated oxygen sensor alternates correctly.

B → See step   7 

C → See step   8 

D → See step   10 

A: Go to next step 

1. Check for exhaust gas leaks.

   OK

   No gas leaks.

NG → See step   14 

OK: 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 and warm it up until the engine coolant temperature reaches 75°C (167°F) or higher.

   HINT: 

   The A/C switch and all accessory switches should be off.

6. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position / Data List / Primary / MAP.
7. Check the engine idling condition and MAP values in the Data List while performing the Active Test.

   HINT: 

   • Do not leave the EGR valve open for 10 seconds or more during the Active Test.
   • Be sure to return the EGR valve to step 0 when the Active Test is completed.
   • Do not open the EGR valve 30 steps or more during the Active Test.

   OK

   MAP and idling condition change in response to EGR step position.

   Standard

   -	EGR Step Position (Active Test)
   	0 Steps	0 to 30 Steps
   Idling condition	Steady idling	Idling changes from steady to rough idling or engine stalls
   MAP (Data List)	MAP value is 20 to 40 kPa(abs) [150 to 300 mmHg(abs)] (EGR valve is fully closed)	MAP value is at least +10 kPa (75 mmHg) higher than when EGR valve is fully closed

   HINT: 

   During Active Test, if the idling condition does not change in response to EGR step position, then there is probably a malfunction in the EGR valve.

   RESULT
   
   

   Result	Proceed to
   Outside of standard range	A
   Within standard range	B

B → See step   6 

A: Go to next step 

1. Remove the EGR valve assembly. Refer to REMOVAL .
2. Check if the EGR valve is stuck open.

   OK

   EGR valve is tightly closed.

NG → See step   18 

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   15 

1. Check for exhaust gas leaks.

   OK

   No gas leaks.

NG → See step   14 

OK: Go to next step 

1. Replace the heated oxygen sensor. Refer to REMOVAL .

NEXT → See step   15 

1. Check for exhaust gas leaks.

   OK

   No gas leaks.

NG → See step   14 

OK: 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 and warm it up until the engine coolant temperature reaches 75°C (167°F) or higher.

   HINT: 

   The A/C switch and all accessory switches should be off.

6. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position / Data List / Primary / MAP.
7. Check the engine idling condition and MAP values in the Data List while performing the Active Test.

   HINT: 

   • Do not leave the EGR valve open for 10 seconds or more during the Active Test.
   • Be sure to return the EGR valve to step 0 when the Active Test is completed.
   • Do not open the EGR valve 30 steps or more during the Active Test.

   OK

   MAP and idling condition change in response to EGR step position.

   Standard

   -	EGR Step Position (Active Test)
   	0 Steps	0 to 30 Steps
   Idling condition	Steady idling	Idling changes from steady to rough idling or engine stalls
   MAP (Data List)	MAP value is 20 to 40 kPa(abs) [150 to 300 mmHg(abs)] (EGR valve is fully closed)	MAP value is at least +10 kPa (75 mmHg) higher than when EGR valve is fully closed

   HINT: 

   During Active Test, if the idling condition does not change in response to EGR step position, then there is probably a malfunction in the EGR valve.

   RESULT
   
   

   Result	Proceed to
   Outside of standard range	A
   Within standard range	B

B → See step   13 

A: Go to next step 

1. Remove the EGR valve assembly. Refer to REMOVAL .
2. Check if the EGR valve is stuck open.

   OK

   EGR valve is tightly closed.

NG → See step   18 

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 DTC P0171: System Too Lean (Bank 1); DTC P0172: System Too Rich (Bank 1) .

NEXT → See step   15 

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. Turn the power switch on (IG).
7. Turn the Techstream on.
8. Put the engine in inspection mode (maintenance mode). Refer to INSPECTION MODE PROCEDURE .
9. Start the engine.
10. Drive the vehicle in accordance with the driving pattern described in Confirmation Driving Pattern.
11. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
12. 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 front exhaust pipe assembly (TWC: Front and rear catalyst). Refer to COMPONENTS .

NEXT → END