SFI SYSTEM (w/o EGR System), Diagnostic DTC:P0420

DTC Code	DTC Name
P0420	Catalyst System Efficiency Below Threshold (Bank 1)

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.

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).	Gas leaks from exhaust system Air fuel ratio sensor (sensor 1) Heated oxygen sensor (sensor 2) Front exhaust pipe assembly (TWC: Front and rear catalyst)

CATALYST LOCATION

Text in Illustration
*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	-	-

Note

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% or more, and less than 70%
All of the following conditions (a), (b) and (c) are met	-
(a) Mass air flow rate	2.5 gm/sec or more, and less than 50 gm/sec
(b) Front catalyst temperature (estimated)	520°C (968°F) or higher, and below 770°C (1418°F)
(c) Rear catalyst temperature (estimated)	450°C (842°F) or higher, and below 700°C (1292°F)

Tech Tips

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

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 intelligent tester to the DLC3.
Turn the power switch on (IG).
Turn the tester on.
Clear the DTCs (even if no DTCs are stored, perform the clear DTC procedure).
Turn the power switch off and wait for at least 30 seconds.
Turn the power switch on (IG) and turn the tester on.
Put the engine in inspection mode (maintenance mode) Click here.
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 75 km/h (47 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 power switch off and wait for at least 30 seconds [C].
Turn the power switch on (IG) and turn the tester on.
Put the engine in inspection mode (maintenance mode) Click here.
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 75 km/h (47 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.
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, the system is normal.

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.

(a) Connect the intelligent tester to the DLC3 [A].
(b) Turn the power switch on (IG) and turn the tester on [B].
(c) Put the engine in inspection mode (maintenance mode) Click here [C].
(d) Start the engine and warm it up with all the accessories switched off until the engine coolant temperature stabilizes [D].
(e) Run the engine at an engine speed of 2500 rpm for at least 3 minutes [E].

Tech Tips

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, perform step [E] after charging control has completed.
(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].

Tech Tips

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.
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 for A/F Sensor.
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

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 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.

PROCEDURE

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

Connect the intelligent tester to the DLC3.
Turn the power switch on (IG).
Turn the tester on.
Enter the following menus: Powertrain / Engine and ECT / DTC.

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.

GO TO DTC CHART Click here

PERFORM ACTIVE TEST USING INTELLIGENT TESTER (CONTROL THE INJECTION VOLUME FOR A/F SENSOR)

Connect the intelligent tester to the DLC3.
Turn the power switch on (IG).
Turn the tester on.
Put the engine in inspection mode (maintenance mode) Click here.
Start the engine.
Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.

Tech Tips

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.
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.
Perform the Control the Injection Volume for A/F Sensor operation with the engine idling.

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

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
Tester Display (Sensor)	Injection Volume	Status	Voltage
AFS Voltage B1S1 (Air fuel ratio)	12.5%	Rich	Less than 3.1 V
AFS Voltage B1S1 (Air fuel ratio)	-12.5%	Lean	More than 3.4 V
O2S B1S2 (Heated oxygen)	12.5%	Rich	More than 0.55 V
O2S B1S2 (Heated oxygen)	-12.5%	Lean	Less than 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	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	D
Rich	Rich	Actual air fuel ratio rich	-	Extremely rich actual air fuel ratio Gas leaks from exhaust system	D

Lean: During the 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 the Control the Injection Volume for A/F Sensor Active Test, the AFS Voltage B1S1 is consistently below 3.1 V, and the O2S B1S2 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 heated oxygen sensor alternates correctly.

REPLACE AIR FUEL RATIO SENSOR (SENSOR 1) Click here

CHECK FOR EXHAUST GAS LEAK Click here

CHECK FOR EXHAUST GAS LEAK
1. Check for exhaust gas leaks.
  
  OK
  
  No gas leaks.
NG
REPAIR OR REPLACE EXHAUST GAS LEAK POINT Click here

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

Note

When replacing the front exhaust pipe assembly (TWC: Front and rear catalyst) in order to replace the three-way catalytic converter, it is not necessary to replace the heated oxygen sensor.

Tech Tips

Confirm the replacement parts, referring to the illustration in the Catalyst Location.
1. Replace the front exhaust pipe assembly (TWC: Front and rear catalyst) Click here.
NEXT

END
REPLACE AIR FUEL RATIO SENSOR (SENSOR 1)
1. Replace the air fuel ratio sensor Click here.
NEXT
CHECK WHETHER DTC OUTPUT RECURS (DTC P0420) Click here
CHECK FOR EXHAUST GAS LEAK
1. Check for exhaust gas leaks.
  
  OK
  
  No gas leaks.
NG
REPAIR OR REPLACE EXHAUST GAS LEAK POINT Click here

OK
REPLACE HEATED OXYGEN SENSOR (SENSOR 2)
1. Replace the heated oxygen sensor Click here.
NEXT
CHECK WHETHER DTC OUTPUT RECURS (DTC P0420) Click here
CHECK FOR EXHAUST GAS LEAK
1. Check for exhaust gas leaks.
  
  OK
  
  No gas leaks.
NG
REPAIR OR REPLACE EXHAUST GAS LEAK POINT Click here

OK
CHECK 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 Click here.
NEXT
CHECK WHETHER DTC OUTPUT RECURS (DTC P0420) Click here
REPAIR OR REPLACE EXHAUST GAS LEAK POINT
1. Repair or replace exhaust gas leak point.
NEXT

OK
No gas leaks.

OK
No gas leaks.

OK
No gas leaks.

CHECK WHETHER DTC OUTPUT RECURS (DTC P0420)

Connect the intelligent tester to the DLC3.
Turn the power switch on (IG).
Turn the tester on.
Clear the DTCs Click here.
Turn the power switch off and wait for at least 30 seconds.
Drive the vehicle in accordance with the driving pattern described in Confirmation Driving Pattern.
Enter the following menus: Powertrain / Engine and ECT / DTC.

Read the DTCs.

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

END

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

Note

When replacing the front exhaust pipe assembly (TWC: Front and rear catalyst) in order to replace the three-way catalytic converter, it is not necessary to replace the heated oxygen sensor.

Tech Tips

Confirm the replacement parts, referring to the illustration in the Catalyst Location.
1. Replace the front exhaust pipe assembly (TWC: Front and rear catalyst) Click here.
NEXT

END