SFI SYSTEM, Diagnostic DTC:P0420
| DTC Code | DTC Name |
|---|---|
| P0420 | Catalyst System Efficiency Below Threshold (Bank 1) |
DESCRIPTION
The ECM uses sensors mounted in front of and behind the Three-Way Catalytic Converter (TWC) 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 20 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 sets the DTC.
This system determines the deterioration of the entire catalyst system (including the front and rear catalysts), by using the oxygen storage capacity value of the front catalyst, that is more sensitive than the rear catalyst, as the representative value. Therefore, be sure to replace the front and rear catalysts together when catalyst replacement is necessary.
| 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) |
|
CATALYST LOCATION
| *a | Exhaust Manifold Assembly (TWC: Front catalyst) | *b | Air Fuel Ratio Sensor (Sensor 1) |
| *c | Front Exhaust Pipe Assembly | *d | Heated Oxygen Sensor (Sensor 2) |
| *e | Center Exhaust Pipe Assembly (TWC: Rear catalyst) | *f | Tail Exhaust Pipe Assembly |
Note
Replace the exhaust manifold assembly (*a) and center exhaust pipe assembly (*e) together when catalysts replacement is necessary (Excluding air fuel ratio sensor*b).
CONFIRMATION DRIVING PATTERN
Tech Tips
Performing this confirmation driving pattern will activate the catalyst monitor. This is very useful for verifying the completion of a repair.
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Connect the intelligent tester to the DLC3.
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Turn the engine switch on (IG).
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Turn the tester on.
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Clear DTCs (even if no DTCs are stored, perform the clear DTC operation) Click here.
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Turn the engine switch off and wait for at least 30 seconds.
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Turn the engine switch on (IG) and turn the tester on.
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Start the engine and warm it up until the engine coolant temperature is 75°C (167°F) or higher [A].
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Drive the vehicle at approximately 60 km/h (37 mph) for 10 minutes or more [B].
Tech Tips
Drive the vehicle while keeping the engine load as constant as possible.
CAUTION:
When performing the confirmation driving pattern, obey all speed limits and traffic laws.
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Enter the following menus: Powertrain / Engine / DTC [C].
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Read the pending DTCs.
Tech Tips
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If a pending DTC is output, the system is malfunctioning.
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If a pending DTC is not output, perform the following procedure.
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Enter the following menus: Powertrain / Engine / Utility / All Readiness.
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Input the DTC: P0420.
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Check the DTC judgment result.
Tester Display Description NORMAL
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DTC judgment completed
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System normal
ABNORMAL
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DTC judgment completed
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System abnormal
INCOMPLETE
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DTC judgment not completed
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Perform driving pattern after confirming DTC enabling conditions
N/A
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Unable to perform DTC judgment
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Number of DTCs which do not fulfill DTC preconditions has reached ECU memory limit
Tech Tips
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If the judgment result shows NORMAL, the system is normal.
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If the judgment result shows ABNORMAL, the system has a malfunction.
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If the judgment result shows INCOMPLETE or N/A, perform steps [D] through [E].
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Drive the vehicle at a speed between 75 and 100 km/h (47 and 62 mph) for 10 minutes or more [D].
Tech Tips
Drive the vehicle while keeping the engine load as constant as possible.
CAUTION:
When performing the confirmation driving pattern, obey all speed limits and traffic laws.
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Check the DTC judgment result again [E].
CONDITIONING FOR SENSOR TESTING
Tech Tips
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.
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(a) Connect the intelligent tester to the DLC3 (Step "A").
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(b) Start the engine and warm it up with all the accessories switched off until the engine coolant temperature stabilizes (Step "B").
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(c) Run the engine at an engine speed of between 2500 rpm and 3000 rpm for at least 3 minutes (Step "C").
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(d) While running the engine at 3000 rpm for 2 seconds and 2000 rpm for 2 seconds, check the waveforms of the air fuel ratio and heated oxygen sensors using the intelligent tester (Step "D").
Tech Tips
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If either of the voltage outputs of the air fuel ratio or heated oxygen sensors does not fluctuate, or there is noise in the waveform of either sensor, the sensor may be malfunctioning.
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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 following menu items: Powertrain / Engine / Active Test / Control the Injection Volume.
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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).
INSPECTION PROCEDURE
Tech Tips
Malfunctioning areas can be identified by performing the Control the Injection Volume function provided in the Active Test. The Control the Injection Volume function can help to determine whether the air fuel ratio sensor, heated oxygen sensor and other potential trouble areas are malfunctioning.
The following instructions describe how to conduct the Control the Injection Volume operation using the intelligent tester.
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Connect the intelligent tester to the DLC3.
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Start the engine.
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Turn the tester on.
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Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.
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Enter the following menus: Powertrain / Engine / Active Test / Control the Injection Volume.
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Perform the Active Test operation with the engine idling (press the RIGHT or LEFT button to change the fuel injection volume).
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Monitor the output voltages of the air fuel ratio and heated oxygen sensors (AFS Voltage B1S1 and O2S B1S2) displayed on the tester.
Tech Tips
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Change the fuel injection volume within the range of -12% to +12%. The injection volume can be changed in fine gradations.
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Each sensor reacts in accordance with increases and decreases in the fuel injection volume.
| Tester Display (Sensor) | Injection Volume | Status | Voltage |
|---|---|---|---|
| AFS Voltage B1S1 (Air fuel ratio) |
+12% | Rich | Below 3.1 V |
| -12% | Lean | Higher than 3.4 V | |
| O2S B1S2 (Heated oxygen) |
+12% | Rich | Higher than 0.55 V |
| -12% | Lean | Below 0.4 V |
Note
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.
| Case | Air Fuel Ratio Sensor (Sensor 1) Output Voltage | Heated Oxygen Sensor (Sensor 2) Output Voltage | Main Suspected Trouble Area |
|---|---|---|---|
| 1 |   |
 |
- |
| 2 |  |
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| 3 | |
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| 4 | |
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Following the Control the Injection Volume procedure enables technicians to check and graph the voltage outputs of both the air fuel ratio and heated oxygen sensors.
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To display the graph, enter the following menus: Powertrain / Engine / Active Test / Control the Injection Volume / AFS Voltage B1S1 and O2S B1S2; and then press the graph button on the Data List view.
Tech Tips
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If a malfunction cannot be found when troubleshooting DTC P0420, a lean or rich abnormality may be the cause. Perform troubleshooting by following the inspection procedure for P0171 (System Too Lean) and P0172 (System Too Rich).
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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.
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Sensor 1 refers to the sensor closest to the engine assembly.
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Sensor 2 refers to the sensor farthest away from the engine assembly.
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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 be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.
PROCEDURE
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CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0420)
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Connect the intelligent tester to the DLC3.
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Turn the engine switch on (IG).
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Turn the tester on.
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Enter the following menus: Powertrain / Engine / DTC.
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Read the DTCs.
Result Result Proceed to DTC P0420 is output A DTC P0420 and other DTCs are output B Tech Tips
If any DTCs other than P0420 are output, troubleshoot those DTCs first.
B 
GO TO DTC CHART Click here
A 
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PERFORM ACTIVE TEST USING INTELLIGENT TESTER (CONTROL THE INJECTION VOLUME)
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Connect the intelligent tester to the DLC3.
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Start the engine and warm it up.
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Turn the tester on.
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Run the engine at an engine speed of 2500 rpm for approximately 90 seconds.
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Enter the following menus: Powertrain / Engine / Active Test / Control the Injection Volume / All Data / AFS Voltage B1S1 and O2S B1S2.
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Perform the Active Test operation with the engine idling (press the RIGHT or LEFT button to change the fuel injection volume).
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Monitor the voltage outputs of the air fuel ratio sensor and heated oxygen sensor (AFS Voltage B1S1 and O2S B1S2) displayed on the tester.
Tech Tips
-
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.
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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 -12% Lean Higher than 3.4 V O2S B1S2
(Heated oxygen)
+12% Rich Higher than 0.55 V -12% Lean Below 0.4 V Result Status
AFS Voltage B1S1
Status
O2S B1S2
Actual air fuel ratio, air fuel ratio sensor and
heated oxygen sensor condition
Misfire Main Suspected Trouble Area Proceed to Lean/Rich Lean/Rich Normal -
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Three-way catalytic converter
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Gas leak from exhaust system
A Lean Lean/Rich Air fuel ratio sensor malfunction -
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Air fuel ratio sensor
B Rich Lean/Rich Air fuel ratio sensor malfunction -
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Air fuel ratio sensor
Lean/Rich Lean Heated oxygen sensor malfunction -
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Heated oxygen sensor
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Gas leak from exhaust system
C Lean/Rich Rich Heated oxygen sensor malfunction -
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Heated oxygen sensor
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Gas leak from exhaust system
Lean Lean Actual air fuel ratio lean May occur
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Extremely lean actual air fuel ratio
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Gas leak from exhaust system
D Rich Rich Actual air fuel ratio rich -
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Extremely rich actual air fuel ratio
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Gas leak from exhaust system
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Lean: During Control the Injection Volume, the air fuel ratio sensor output voltage (AFS Voltage B1S1) is consistently higher than 3.4 V, and the heated oxygen sensor output voltage (O2S B1S2) is consistently below 0.4 V.
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Rich: During Control the Injection Volume, the AFS Voltage B1S1 is consistently below 3.1 V, and the O2S B1S2 is consistently higher than 0.55 V.
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Lean/Rich: During Control the Injection Volume of the Active Test, the output voltage of the air fuel ratio sensor and heated oxygen sensor alternate correctly.
Tech Tips
Refer to "Data List / Active Test" [AFS Voltage B1S1 and O2S B1S2] Click here.
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B 
REPLACE AIR FUEL RATIO SENSOR Click here
C
CHECK FOR EXHAUST GAS LEAK Click here
D
CHECK FOR EXHAUST GAS LEAK Click here
A
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CHECK FOR EXHAUST GAS LEAK
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Check for exhaust gas leaks.
OK No gas leaks.
NG
REPAIR OR REPLACE EXHAUST GAS LEAK POINT Click here
OK
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REPLACE EXHAUST MANIFOLD ASSEMBLY (TWC: FRONT CATALYST) AND CENTER EXHAUST PIPE ASSEMBLY (TWC: REAR CATALYST)
Note
Replace the exhaust manifold assembly (TWC: Front catalyst) and the center exhaust pipe assembly (TWC: Rear catalyst) together when catalyst replacement is necessary.
Tech Tips
Confirm the replacement parts, referring to the illustration in the Catalyst Location.
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Replace the exhaust manifold assembly (TWC: Front catalyst) Click here.
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Replace the center exhaust pipe assembly (TWC: Rear catalyst) Click here.
NEXT 
END
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REPLACE AIR FUEL RATIO SENSOR
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Replace the air fuel ratio sensor Click here.
NEXT
CHECK WHETHER DTC OUTPUT RECURS (DTC P0420) Click here
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CHECK FOR EXHAUST GAS LEAK
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Check for exhaust gas leaks.
OK No gas leaks.
NG
REPAIR OR REPLACE EXHAUST GAS LEAK POINT Click here
OK
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REPLACE OXYGEN SENSOR
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Replace the heated oxygen sensor Click here.
NEXT
CHECK WHETHER DTC OUTPUT RECURS (DTC P0420) Click here
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CHECK FOR EXHAUST GAS LEAK
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Check the exhaust gas leaks.
OK No gas leaks.
NG
REPAIR OR REPLACE EXHAUST GAS LEAK POINT Click here
OK
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CHECK CAUSE OF EXTREMELY RICH OR LEAN ACTUAL AIR FUEL RATIO
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Check the cause of extremely rich or lean actual air fuel ratio, referring to the DTC P0171 Inspection Procedure Click here.
NEXT
CHECK WHETHER DTC OUTPUT RECURS (DTC P0420) Click here
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REPAIR OR REPLACE EXHAUST GAS LEAK POINT
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Repair or replace exhaust gas leak point.
NEXT
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CHECK WHETHER DTC OUTPUT RECURS (DTC P0420)
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Connect the intelligent tester to the DLC3.
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Turn the engine switch on (IG).
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Turn the tester on.
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Clear the DTCs Click here.
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Turn the engine switch off and wait for at least 30 seconds.
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Turn the engine switch on (IG).
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Turn the tester on.
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Start the engine.
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Drive the vehicle in accordance with the driving pattern described in Confirmation Driving Pattern.
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Enter the following menus: Powertrain / Engine / DTC.
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Read the DTCs.
Result Result Proceed to DTC P0420 is output A DTC is not output
(No pending DTCs output)
B
B
END
A
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INSPECT EXHAUST MANIFOLD ASSEMBLY (TWC: FRONT CATALYST) AND CENTER EXHAUST PIPE ASSEMBLY (TWC: REAR CATALYST)
Note
Replace the exhaust manifold assembly (TWC: Front catalyst) and the center exhaust pipe assembly (TWC: Rear catalyst) together when catalyst replacement is necessary.
Tech Tips
Confirm the replacement parts, referring to the illustration in the Catalyst Location.
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Replace the exhaust manifold assembly (TWC: Front catalyst) Click here.
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Replace the center exhaust pipe assembly (TWC: Rear catalyst) Click here.
NEXT
END
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