Code P0420 Catalyst System Efficiency Below Threshold P0420 2ZR-FXE

DTC P0420 Catalyst System Efficiency Below Threshold (Bank 1)

  1. Monitor description

  2. Catalyst location

  3. Monitor strategy

  4. Typical enabling conditions

  5. Confirmation driving pattern

  6. Conditioning for sensor testing

  7. Inspection procedure

  8. Check any other dtcs output (in addition to dtc p0420)

  9. Perform active test using intelligent tester (control the injection volume)

  10. Check for exhaust gas leak

  11. Perform active test using intelligent tester (control the egr step position)

  12. Inspect egr valve assembly

  13. Replace front exhaust pipe assembly (twc: front and rear catalyst)

  14. Replace air fuel ratio sensor (sensor 1)

  15. Check for exhaust gas leak

  16. Replace heated oxygen sensor (sensor 2)

  17. Inspect for exhaust gas leak

  18. Perform active test using intelligent tester (control the egr step position)

  19. Inspect egr valve assembly

  20. Check engine to determine cause of extremely rich or lean actual air fuel ratio

  21. Check whether dtc output recurs

  22. Replace front exhaust pipe assembly (twc: front and rear catalyst)

Monitor description

The ECM uses sensors mounted in front of and behind the three-way catalytic converter to monitor its efficiency. The first sensor, the air fuel ratio sensor, sends pre-catalyst information to the ECM. The second sensor, the heated oxygen sensor, sends post-catalyst information to the ECM. In order to detect any deterioration in the three-way catalytic converter, the ECM calculates the oxygen storage capacity of the three-way catalytic converter. This calculation is based on the voltage output of the heated oxygen sensor while performing active air fuel ratio control. The oxygen storage capacity value is an indication of the oxygen storage capacity of the three-way catalytic converter. When the vehicle is being driven with a warm engine, active air fuel ratio control is performed for approximately 15 to 25 seconds. When it is performed, the ECM deliberately sets the air fuel ratio to lean or rich levels. If the cycle of the waveform for the heated oxygen sensor is long, the oxygen storage capacity is great. There is a direct correlation between the heated oxygen sensor and the oxygen storage capacity of the three-way catalytic converter. The ECM uses the oxygen storage capacity value to determine the state of the three-way catalytic converter. If any deterioration has occurred, it illuminates the MIL and stores the DTC.

DTC No. DTC Detection Condition Trouble Area
P0420 Oxygen storage capacity value smaller than standard value under active air fuel ratio control (2 trip detection logic).
  1. Gas leaks from exhaust system
  2. Air fuel ratio sensor (sensor 1)
  3. Heated oxygen sensor (sensor 2)
  4. Front exhaust pipe assembly (TWC: Front and rear catalyst)
  5. EGR valve assembly

Catalyst location

Lexus DTC P0420 Catalyst location

 

Text in Illustration
*A w/ Exhaust Heat Recirculation System *B w/o Exhaust Heat Recirculation System
*1 Air Fuel Ratio Sensor (Sensor 1) *2 Heated Oxygen Sensor (Sensor 2)
*3 Exhaust Manifold Sub-assembly *4 Front Exhaust Pipe Assembly
*5 Tail Exhaust Pipe Assembly *6 TWC: Front Catalyst
*7 TWC: Rear Catalyst - -

When replacing the front exhaust pipe assembly in order to replace the three-way catalytic converter, it is not necessary to replace the heated oxygen sensor.

Monitor strategy

Required Sensors/Components (Main) Air fuel ratio sensor Heated oxygen sensor
Required Sensors/Components (Related) Intake air temperature sensor Mass air flow meter sub-assembly Crankshaft position sensor Engine coolant temperature sensor
Frequency of Operation Once per driving cycle

TYPICAL ENABLING CONDITIONS

Auxiliary battery voltage 11 V or more
Intake air temperature -10°C (14°F) or higher
Engine coolant temperature 75°C (167°F) or higher
Atmospheric pressure 76 kPa (570 mmHg) or more
Idling OFF
Engine speed Less than 4000 rpm
Air fuel ratio sensor Activated
Fuel system status Closed loop
Engine load 10 to 70%
All of the following conditions (a), (b) and (c) are met -
(a) Mass air flow rate 2.5 to 50 gm/sec
(b) Front catalyst temperature (estimated) 520 to 770°C (968 to 1418°F)
(c) Rear catalyst temperature (estimated) 450 to 700°C (842 to 1292°F)

HINT:

The estimated catalyst temperature can be read in the Data List using the intelligent tester.

Confirmation driving pattern

HINT:

Performing this confirmation pattern will activate the catalyst monitor. This is very useful for verifying the completion of a repair.

Lexus DTC P0420 Confirmation driving pattern
  1. Connect the intelligent tester to the DLC3.
  2. Turn the power switch on (IG).
  3. Turn the tester on.
  4. Clear the DTCs (even if no DTCs are stored, perform the clear DTC operation).
  5. Turn the power switch off and wait for at least 30 seconds.
  6. Turn the power switch on (IG) and turn the tester on.
  7. Put the engine in inspection mode (maintenance mode) .
  8. Start the engine and warm it up until the engine coolant temperature is 75°C (167°F) or higher [A].
  9. Drive the vehicle at approximately 60 to 100 km/h (37 to 62 mph) for 10 minutes or more [B].

    CAUTION:

    When performing the confirmation driving pattern, obey all speed limits and traffic laws.

    HINT:

    Drive the vehicle while keeping the engine load as constant as possible.

  10. Enter the following menus: Powertrain / Engine and ECT / DTC [C].
  11. Read the pending DTCs.

    HINT:

    1. If a pending DTC is output, system is malfunction.
    2. If a pending DTC is not output, perform the following procedure.
  12. Input the DTC: P0420.
  13. Check the DTC judgment result.
    Tester Display Description
    NORMAL
    1. DTC judgment completed
    2. System normal
    ABNORMAL
    1. DTC judgment completed
    2. System abnormal
    INCOMPLETE
    1. DTC judgment not completed
    2. Perform driving pattern after confirming DTC enabling conditions
    UNKNOWN
    1. Unable to perform DTC judgment
    2. Number of DTCs which do not fulfill DTC preconditions has reached ECU memory limit

    HINT:

    1. If the judgment result shows NORMAL, the system is normal.
    2. If the judgment result shows ABNORMAL, the system has a malfunction.
    3. If the judgment result shows INCOMPLETE or UNKNOWN, perform the following procedure.
  14. Drive the vehicle at a speed between 75 and 100 km/h (47 and 62 mph) for 10 minutes or more [D].

    CAUTION:

    When performing the confirmation driving pattern, obey all speed limits and traffic laws.

    HINT:

    Drive the vehicle while keeping the engine load as constant as possible.

  15. Check the DTC judgment result again [E].

Conditioning for sensor testing

HINT:

Perform the operation with the engine speeds and time durations described below prior to checking the waveforms of the air fuel ratio sensor and heated oxygen sensor. This is in order to activate the sensors sufficiently to obtain the appropriate inspection results.

Lexus DTC P0420 Conditioning for sensor testing
  1. (a) Connect the intelligent tester to the DLC3 [A].
  2. (b) Turn the power switch on (IG) and turn the tester on [B].
  3. (c) Put the engine in inspection mode (maintenance mode) [C].
  4. (d) Start the engine and warm it up with all the accessories switched off until the engine coolant temperature stabilizes [D].
  5. (e) Run the engine at an engine speed of 2500 rpm for at least 3 minutes [E].
  6. (f) While running the engine at 2500 rpm for 2 seconds and then 1500 rpm for 2 seconds, check the waveforms of the air fuel ratio and heated oxygen sensors using the tester [F].

HINT:

  1. If either of the voltage outputs of the air fuel ratio or heated oxygen sensor does not fluctuate, or there is noise in the waveform of either sensor, the sensor may be malfunctioning.
  2. If the voltage outputs of both the sensors remain lean or rich, the air fuel ratio may be extremely lean or rich. In such cases, perform the Active Test operation by entering the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume.
  3. If the three-way catalytic converter has deteriorated, the heated oxygen sensor (located behind the three-way catalytic converter) voltage output fluctuates up and down frequently, even under normal driving conditions (active air fuel ratio control is not performed).

Lexus DTC P0420 voltage output fluctuates up and down frequently

Inspection procedure

HINT:

  1. After performing repairs, drive the vehicle in accordance with the driving pattern described in Confirmation Driving Pattern and check if DTC P0420 is output again. If a DTC is output again, replace the catalyst if it has not been replaced already.
  2. Sensor 1 refers to the sensor closest to the engine assembly.
  3. Sensor 2 refers to the sensor farthest away from the engine assembly.
  4. Read freeze frame data using the intelligent tester. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, if the engine was warmed up or not, if the air fuel ratio was lean or rich, and other data from the time the malfunction occurred.

1.CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0420)

  1. Connect the intelligent tester to the DLC3.

  1. Turn the power switch on (IG).

  1. Turn the tester on.

  1. Enter the following menus: Powertrain / Engine and ECT / DTC.

  1. 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  
GO TO DTC CHART
 
OK  
   

2.PERFORM ACTIVE TEST USING INTELLIGENT TESTER (CONTROL THE INJECTION VOLUME)

  1. Connect the intelligent tester to the DLC3.

  1. Turn the power switch on (IG).

  1. Turn the tester on.

  1. Put the engine in inspection mode (maintenance mode) .

  1. Start the engine.

  1. Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.

  1. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume.

  1. Perform the Control the Injection Volume operation with the engine idling.

  1. Monitor the output voltages of the air fuel ratio and heated oxygen sensors (AFS Voltage B1S1 and O2S B1S2) displayed on the tester.

    HINT:

    1. Change the fuel injection volume within the range of -12.0% to +12.0%. The injection volume can be changed in fine gradations.
    2. 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.
    3. If the sensor output voltage does not change (almost no reaction) while performing the Active Test, the sensor may be malfunctioning.
    Standard
    Tester 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 -
    1. Tree-way catalytic converter
    2. Gas leaks from exhaust system
    3. 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 -
    1. Heated oxygen sensor
    2. Gas leaks from exhaust system
    		 C
    Lean/Rich Rich Heated oxygen sensor malfunction -
    1. Heated oxygen sensor
    2. Gas leaks from exhaust system
    		 C
    Lean Lean Actual air fuel ratio lean May occur
    1. Extremely rich or lean actual air fuel ratio
    2. Gas leaks from exhaust system
    3. EGR valve assembly
    		 D
    Rich Rich Actual air fuel ratio rich -
    1. Extremely rich or lean actual air fuel ratio
    2. Gas leaks from exhaust system
    3. EGR valve assembly
    		 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.

    HINT:

    Refer to "Data List / Active Test" [AFS Voltage B1S1 and O2S B1S2] .

  B  
Go to step 7
 
  C  
Go to step 8
 
  D  
Go to step 10
 
OK  
   

3.CHECK FOR EXHAUST GAS LEAK

  1. Inspect for exhaust gas leaks from the exhaust manifold sub-assembly and exhaust pipes.

OK:

No gas leaks.

  NG  
REPAIR OR REPLACE EXHAUST GAS LEAK POINT
 
OK  
   

4.PERFORM ACTIVE TEST USING INTELLIGENT TESTER (CONTROL THE EGR STEP POSITION)

  1. Connect the intelligent tester to the DLC3.

  1. Turn the power switch on (IG).

  1. Turn the tester on.

  1. Put the engine in inspection mode (maintenance mode) .

  1. 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.

  1. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position / Data List / All Data / Throttle Idle Position and MAP.

  1. Confirm that the Throttle Idle Position is ON and check the engine idling condition and MAP values in the Data List while performing the Active Test.

    HINT:

    1. Do not leave the EGR valve open for 10 seconds or more during the Active Test.
    2. Be sure to return the EGR valve to step 0 when the Active Test is completed.
    3. 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 when Throttle Idle Position is ON in Data List.

    Standard:

    - EGR Step Position (Active Test)
    0 Steps 0 to 30 Steps
    Idling condition Steady idling Idling changes from steady to rough idling or stalls
    MAP (Data List) MAP value is 20 to 40 kPa (150 to 300 mmHg) (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  
Go to step 6
 
OK  
   

5.INSPECT EGR VALVE ASSEMBLY

  1. Remove the EGR valve assembly .

  1. Check if the EGR valve is stuck open.

    OK:

    EGR valve is tightly closed.

  NG  
REPLACE EGR VALVE ASSEMBLY
 
OK  
   

6.REPLACE FRONT EXHAUST PIPE ASSEMBLY (TWC: FRONT AND REAR CATALYST)

NOTICE:

When replacing the front exhaust pipe assembly in order to replace the three-way catalytic converter, it is not necessary to replace the heated oxygen sensor.

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) .

NEXT  
   
END

7.REPLACE AIR FUEL RATIO SENSOR (SENSOR 1)

  1. Replace the air fuel ratio sensor .

  NEXT  
Go to step 14
 

8.CHECK FOR EXHAUST GAS LEAK

  1. Inspect for exhaust gas leaks from the exhaust manifold sub-assembly and exhaust pipes.

OK:

No gas leaks.

  NG  
REPAIR OR REPLACE EXHAUST GAS LEAK POINT
 
OK  
   

9.REPLACE HEATED OXYGEN SENSOR (SENSOR 2)

  1. Replace the heated oxygen sensor .

  NEXT  
Go to step 14
 

10.INSPECT FOR EXHAUST GAS LEAK

  1. Inspect for exhaust gas leaks from the exhaust manifold sub-assembly and exhaust pipes.

OK:

No gas leaks.

  NG  
REPAIR OR REPLACE EXHAUST GAS LEAK POINT
 
OK  
   

11.PERFORM ACTIVE TEST USING INTELLIGENT TESTER (CONTROL THE EGR STEP POSITION)

  1. Connect the intelligent tester to the DLC3.

  1. Turn the power switch on (IG).

  1. Turn the tester on.

  1. Put the engine in inspection mode (maintenance mode) .

  1. 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.

  1. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position / Data List / All Data / Throttle Idle Position and MAP.

  1. Confirm that the Throttle Idle Position is ON and check the engine idling condition and MAP values in the Data List while performing the Active Test.

    HINT:

    1. Do not leave the EGR valve open for 10 seconds or more during the Active Test.
    2. Be sure to return the EGR valve to step 0 when the Active Test is completed.
    3. 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 when Throttle Idle Position is ON in Data List.

    Standard:

    - EGR Step Position (Active Test)
    0 Steps 0 to 30 Steps
    Idling condition Steady idling Idling changes from steady to rough idling or stalls
    MAP (Data List) MAP value is 20 to 40 kPa (150 to 300 mmHg) (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  
Go to step 13
 
OK  
   

12.INSPECT EGR VALVE ASSEMBLY

  1. Remove the EGR valve assembly .

  1. Check if the EGR valve is stuck open.

    OK:

    EGR valve is tightly closed.

  NG  
REPLACE EGR VALVE ASSEMBLY
 
OK  
   

13.CHECK ENGINE TO DETERMINE CAUSE OF EXTREMELY RICH OR LEAN ACTUAL AIR FUEL RATIO

  1. Check the case of extremely rich or lean actual air fuel ratio, referring to the DTC P0171 Inspection Procedure .

NEXT  
   

14.CHECK WHETHER DTC OUTPUT RECURS

  1. Connect the intelligent tester to the DLC3.

  1. Turn the power switch on (IG).

  1. Turn the tester on.

  1. Clear the DTCs.

  1. Turn the power switch off and wait for at least 30 seconds.

  1. Drive the vehicle in accordance with the driving pattern described in Confirmation Driving Pattern.

  1. Enter the following menus: Powertrain / Engine and ECT / DTC.

  1. Read the DTCs.

    Result
    Result Proceed to
    DTC P0420 is output A
    DTC is not output (No pending DTCs output) B
  B  
END
 
OK  
   

15.REPLACE FRONT EXHAUST PIPE ASSEMBLY (TWC: FRONT AND REAR CATALYST)

NOTICE:

When replacing the front exhaust pipe assembly in order to replace the three-way catalytic converter, it is not necessary to replace the heated oxygen sensor.

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) .

NEXT  
   
END
p0420 toyota