MONITOR 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 30 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, the ECM will illuminate the MIL and store a 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. | Detection Item | DTC Detection Condition | Trouble Area | MIL | Memory |
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P0420 | Catalyst System Efficiency Below Threshold (Bank 1) | The oxygen storage capacity value is less than the standard value under active air fuel ratio control (2 trip detection logic). |
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Comes on (Euro-OBD) / - (Except Euro-OBD) | DTC stored (Euro-OBD) / - (Except Euro-OBD) |
CATALYST LOCATION
*1 | Air Fuel Ratio Sensor (Sensor 1) | *2 | Heated Oxygen Sensor (Sensor 2) |
*3 | TWC: Front Catalyst | *4 | TWC: Rear Catalyst |
*5 | Exhaust Manifold Converter Sub-assembly | *6 | Front Exhaust Pipe Assembly |
*7 | Center Exhaust Pipe Assembly | *8 | Tail Exhaust Pipe Assembly |
Note
Replace the exhaust manifold converter sub-assembly (*5) and the center exhaust pipe assembly (*7) together when catalyst replacement is necessary. (Excluding air fuel ratio sensor*1 and heated oxygen sensor*2)
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
Battery voltage | 11 V or higher |
Intake air temperature | -10°C (14°F) or higher |
Engine coolant temperature | 75°C (167°F) or higher |
Atmospheric pressure | 76 kPa(abs) [570 mmHg(abs)] or higher |
Idling | Off |
Engine speed | Less than 4000 rpm |
Air fuel ratio sensor status | Activated |
Fuel system status | Closed loop |
Engine load | 10% or higher, and less than 90% |
All of the following conditions are met | 1, 2 and 3 |
1. Mass air flow | 2.5 gm/sec or more, and less than 70 gm/sec |
2. Front catalyst temperature (estimated) | 685°C (1265°F) or higher, and less than 875°C (1607°F) |
3. Rear catalyst temperature (estimated) | 490°C (914°F) or higher, and less than 770°C (1418°F) |
Shift position | 5th or higher |
CONFIRMATION DRIVING PATTERN
Tech Tips
Performing this confirmation driving pattern will activate the catalyst efficiency monitor. This is very useful for verifying the completion of a repair.
Connect the GTS to the DLC3.
Turn the engine switch on (IG).
Turn the GTS on.
Clear the DTCs (even if no DTCs are stored, perform the clear DTC procedure).
Turn the engine switch off and wait for at least 30 seconds.
Turn the engine switch on (IG) and turn the GTS on.
Start the engine and warm it up until the engine coolant temperature is 75°C (167°F) or higher [A].
Drive the vehicle at approximately 60 km/h (37 mph) for 10 minutes or more [B].
CAUTION:
When performing the confirmation driving pattern, obey all speed limits and traffic laws.
Tech Tips
Drive the vehicle while keeping the engine load as constant as possible.
Turn the engine switch off and wait for at least 30 seconds [C].
Turn the engine switch on (IG) and turn the GTS on.
Start the engine and warm it up until the engine coolant temperature is 75°C (167°F) or higher [D].
Drive the vehicle at approximately 60 km/h (37 mph) for 10 minutes or more [E].
CAUTION:
When performing the confirmation driving pattern, obey all speed limits and traffic laws.
Tech Tips
Drive the vehicle while keeping the engine load as constant as possible.
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes [F].
Read the pending DTCs.
Tech Tips
If a pending DTC is output, the system is malfunctioning.
If a pending DTC is not output, perform the following procedure.
Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
Input the DTC: P0420.
Check the DTC judgment result.
GTS Display | Description |
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NORMAL |
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ABNORMAL |
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INCOMPLETE |
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N/A |
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Tech Tips
If the judgment result shows NORMAL, the system is normal.
If the judgment result shows ABNORMAL, the system has a malfunction.
If the judgment result shows INCOMPLETE or N/A and no pending DTC is output, perform the following procedure.
Drive the vehicle at a speed between 75 and 100 km/h (47 and 62 mph) for 10 minutes or more [G].
CAUTION:
When performing the confirmation driving pattern, obey all speed limits and traffic laws.
Tech Tips
Drive the vehicle while keeping the engine load as constant as possible.
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes [H].
Read the pending DTCs.
Tech Tips
If a pending DTC is output, the system is malfunctioning.
If a pending DTC is not output, perform the following procedure.
Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
Input the DTC: P0420.
Check the DTC judgment result.
GTS Display | Description |
---|---|
NORMAL |
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ABNORMAL |
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INCOMPLETE |
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N/A |
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Tech Tips
If the judgment result shows NORMAL, the system is normal.
If the judgment result shows ABNORMAL, the system has a malfunction.
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 and heated oxygen sensors. This is to activate the sensors sufficiently to obtain appropriate inspection results.
(a) Connect the GTS to the DLC3.
(b) Start the engine and warm it up with all the accessories switched off until the engine coolant temperature stabilizes.
(c) Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / AFS Voltage B1S1 and O2S B1S2.
(c) Run the engine at an engine speed of between 2500 rpm and 3000 rpm for at least 3 minutes.
(d) While running the engine at 3000 rpm for 2 seconds, and then 2000 rpm for 2 seconds, check the waveforms of the air fuel ratio and heated oxygen sensors using the GTS.
Tech Tips
If the voltage output of either the air fuel ratio or heated oxygen sensor does not fluctuate, or there is a noise in the waveform of either sensor, the sensor may be malfunctioning.
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 Control the Injection Volume for A/F Sensor Active Test using the GTS.
If the Three-way Catalytic Converter (TWC) has deteriorated, the heated oxygen sensor (located behind the Three-way Catalytic Converter [TWC]) voltage output fluctuates up and down frequently, even under normal driving conditions (active air fuel ratio control is not performed).
CAUTION / NOTICE / HINT
Tech Tips
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).
Sensor 1 refers to the sensor closest to the engine assembly.
Sensor 2 refers to the sensor farthest away from the engine assembly.
Read freeze frame data using the GTS. 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.
PROCEDURE
CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0420)
Connect the GTS to the DLC3.
Turn the engine switch on (IG).
Turn the GTS on.
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
Read the DTCs.
Result | ||||||
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Tech Tips
If any DTCs other than P0420 are output, troubleshoot those DTCs first.
B |
GO TO DTC CHART Click here |
A |
PERFORM ACTIVE TEST USING GTS (CONTROL THE INJECTION VOLUME FOR A/F SENSOR)
Connect the GTS to the DLC3.
Start the engine and warm it up.
Turn the GTS on.
Run the engine at an engine speed of 2500 rpm for approximately 90 seconds.
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.
Active Test Display |
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Control the Injection Volume for A/F Sensor |
Data List Display |
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AFS Voltage B1S1 |
O2S B1S2 |
Perform the Active Test operation with the engine idling (press the RIGHT or LEFT button to change the fuel injection volume).
Monitor the voltage outputs of the air fuel ratio sensor and heated oxygen sensor (AFS Voltage B1S1 and O2S B1S2) displayed on the GTS.
Tech Tips
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.
Standard | ||||||||||||||||||
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Result | |||||||||||||||||||||||||||||||||||||||||||||
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Lean: During Control the Injection Volume for A/F Sensor Active Test, 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.
Rich: During Control the Injection Volume for A/F Sensor Active Test, AFS Voltage B1S1 is consistently below 3.1 V, and O2S B1S2 is consistently higher than 0.55 V.
Lean/Rich: During Control the Injection Volume for A/F Sensor Active Test, the output voltage of the air fuel ratio sensor and heated oxygen sensor alternate correctly.
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 |
CHECK FOR EXHAUST GAS LEAK
Check for exhaust gas leaks.
OK |
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No gas leaks. |
Result | |||
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OK |
GO TO STEP 11 Click here |
NG |
GO TO STEP 9 Click here |
REPLACE AIR FUEL RATIO SENSOR
Replace the air fuel ratio sensor.
Result | ||
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NEXT |
GO TO STEP 10 Click here |
CHECK FOR EXHAUST GAS LEAK
Check for exhaust gas leaks.
OK |
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No gas leaks. |
Result | |||
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NG |
GO TO STEP 9 Click here |
OK |
REPLACE HEATED OXYGEN SENSOR
Replace the heated oxygen sensor.
Result | ||
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NEXT |
GO TO STEP 10 Click here |
CHECK FOR EXHAUST GAS LEAK
Check for exhaust gas leaks.
OK |
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No gas leaks. |
Result | |||
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NG |
REPAIR OR REPLACE EXHAUST GAS LEAK POINT Click here |
OK |
CHECK CAUSE OF EXTREMELY RICH OR LEAN ACTUAL AIR FUEL RATIO
Check the cause of extremely rich or lean actual air fuel ratio, referring to the DTC P0171 and P0172 Inspection Procedure.
Result | ||
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NEXT |
GO TO STEP 10 Click here |
REPAIR OR REPLACE EXHAUST GAS LEAK POINT
Repair or replace exhaust gas leak point.
Tech Tips
Perform "Inspection After Repair" after repairing or replacing the exhaust system.
Result | ||
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NEXT |
CHECK WHETHER DTC OUTPUT RECURS (DTC P0420)
Connect the GTS to the DLC3.
Turn the engine switch on (IG).
Turn the GTS on.
Clear the DTCs.
Turn the engine switch off and wait for at least 30 seconds.
Start the engine.
Turn the GTS on.
Drive the vehicle in accordance with the driving pattern described in Confirmation Driving Pattern.
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
Read the DTCs.
Result | ||||||
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B |
END |
A |
REPLACE EXHAUST MANIFOLD CONVERTER SUB-ASSEMBLY (TWC: FRONT CATALYST) AND CENTER EXHAUST PIPE ASSEMBLY (TWC: REAR CATALYST)
Note
Replace the exhaust manifold converter sub-assembly (TWC: Front catalyst) and 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.
Replace the exhaust manifold converter sub-assembly (TWC: Front catalyst).
Replace the center exhaust pipe assembly (TWC: Rear catalyst).
Result | ||
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NEXT |
END |