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 (A/F) sensor, sends pre-catalyst information to the ECM. The second sensor, the Heated Oxygen (HO2) sensor, sends post-catalyst information to the ECM.

In order to detect any deterioration in the TWC, the ECM calculates the Oxygen Storage Capacity (OSC) of the TWC. This calculation is based on the voltage output of the HO2 sensor while performing active air fuel ratio control, rather than the conventional detecting method, which uses the locus ratio.

The OSC value is an indication of the oxygen storage capacity of the TWC. 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 rich-lean cycle of the HO2 sensor is long, the OSC becomes greater. There is a direct correlation between the OSCs of the HO2 sensor and the TWC.

The ECM uses the OSC value to determine the state of the TWC. If any deterioration has occurred, it illuminates the MIL and stores the DTC.


DTC No.	DTC Detection Condition	Trouble Area
P0420	The Oxygen Storage Capacity (OSC) value is less than the standard value under active air fuel ratio control (2 trip detection logic).	Front exhaust pipe (TWC: Front catalyst and rear catalyst) Gas leak from exhaust system Air fuel ratio sensor (sensor 1) Heated oxygen sensor (sensor 2)

CATALYST LOCATION

Table 1. Text in Illustration
*1	Exhaust Manifold	*2	TWC: Front Catalyst
*3	Front Exhaust Pipe	*4	TWC: Rear Catalyst
*5	Tail Exhaust Pipe	-	-

CONFIRMATION DRIVING PATTERN

Tip:

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 ignition switch to ON.
Turn the GTS on.
Clear DTCs (even if no DTCs are stored, perform the clear DTC operation).
Turn the ignition switch off and wait for at least 30 seconds.
Turn the ignition switch to ON 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.

Tip:
Drive the vehicle while keeping the engine load as constant as possible.
Turn the ignition switch off and wait for at least 30 seconds [C].
Turn the ignition switch to ON 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.

Tip:
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.
Tip:
- 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 63 mph) for 10 minutes or more [G].

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

Tip:
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.
Tip:
- If a pending DTC is output, the system is malfunctioning.
- If a pending DTC is not output, system is normal.

CONDITIONING FOR SENSOR TESTING

Tip:

Perform the operation with the engine speeds and time durations described below prior to checking the waveforms of the Air Fuel Ratio (A/F) and Heated Oxygen (HO2) sensors. This is in order to activate the sensors sufficiently to obtain the 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) 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 and 2000 rpm alternating at 2 second intervals, check the waveforms of the A/F and HO2 sensors using the GTS.

Tip:

If either voltage output of the A/F or HO2 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, enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.
If the Three-Way Catalytic Converter (TWC) has deteriorated, the HO2 sensor (located behind the TWC) voltage output fluctuates up and down frequently, even under normal driving conditions (active air fuel ratio control is not performed).

CAUTION / NOTICE / HINT

Tip:

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).
Read freeze frame data using the GTS. Freeze frame data records the engine condition when malfunctions are detected. 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.
Sensor 1 refers to the sensor closest to the engine assembly.
Sensor 2 refers to the sensor farthest away from the engine assembly.

PROCEDURE

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

Connect the GTS to the DLC3.
Turn the ignition switch to ON and turn the GTS on.
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

Read the DTCs.

Table 2. Result
Result	Proceed to
DTC P0420 is output	A
DTC P0420 and other DTCs are output	B

Tip:

If any DTCs other than P0420 are output, troubleshoot those DTCs first.

GO TO DTC CHART

(Click here)

PERFORM ACTIVE TEST USING GTS (INJECTION VOLUME CONTROL)

Connect the GTS to the DLC3.
Start the engine and turn the GTS on.
Warm up 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.
Perform the Control the Injection Volume for A/F Sensor operation with the engine in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume).

Monitor the voltage outputs of the A/F and HO2 sensors (AFS Voltage B1S1 and O2S B1S2) displayed on the GTS.

Tip:

The Control the Injection Volume for A/F Sensor operation decreases 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.
If the sensor output voltage does not change (almost no reaction) while performing the Active Test, the sensor may be malfunctioning.

Standard


GTS Display (Sensor)	Injection Volume	Status	Voltage
AFS Voltage B1S1 (A/F)	12.5%	Rich	Below 3.1 V
AFS Voltage B1S1 (A/F)	-12.5%	Lean	Higher than 3.4 V
O2S B1S2 (HO2)	12.5%	Rich	Higher than 0.55 V
O2S B1S2 (HO2)	-12.5%	Lean	Below 0.4 V

Table 3. Result
Status AFS Voltage B1S1	Status O2S B1S2	A/F Condition and A/F and HO2 Sensors Conditions	Main Suspected Trouble Area	Proceed to
Lean/Rich	Lean/Rich	Normal	Three-Way Catalytic Converter (TWC) Gas leak from exhaust system	A
Lean	Lean/Rich	A/F sensor malfunction	A/F sensor	B
Rich	Lean/Rich	A/F sensor malfunction	A/F sensor	B
Lean/Rich	Lean	HO2 sensor malfunction	HO2 sensor Gas leak from exhaust system	C
Lean/Rich	Rich	HO2 sensor malfunction	HO2 sensor Gas leak from exhaust system	C
Lean	Lean	Actual air fuel ratio lean	Extremely rich or lean actual air fuel ratio Gas leak from exhaust system	D
Rich	Rich	Actual air fuel ratio rich	Extremely rich or lean actual air fuel ratio Gas leak from exhaust system	D

Lean: During Control the Injection Volume for A/F Sensor, the air fuel ratio sensor output voltage (AFS) is consistently higher than 3.4 V, and the heated oxygen sensor output voltage (O2S) is consistently below 0.4 V.

Rich: During Control the Injection Volume for A/F Sensor, the AFS is consistently below 3.1 V, and the O2S is consistently higher than 0.55 V.

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

Tip:

Perform "Inspection After Repair" after replacing the air fuel ratio sensor (Click here).

REPLACE AIR FUEL RATIO SENSOR

(Click here)

CHECK FOR EXHAUST GAS LEAKClick here

CHECK EXTREMELY RICH OR LEAN ACTUAL AIR FUEL RATIO, REPAIR CAUSE AND GO TO NEXT STEP

(Click here)

CHECK FOR EXHAUST GAS LEAK
1. Check for exhaust gas leaks.
  
  OK
  
  No gas leaks.
  
  Tip:
  Perform "Inspection After Repair" after repairing or replacing the exhaust system (Click here).
REPLACE FRONT EXHAUST PIPE ASSEMBLY (TWC: FRONT CATALYST AND REAR CATALYST)

(Click here)

REPAIR OR REPLACE EXHAUST GAS LEAK POINT
CHECK FOR EXHAUST GAS LEAK
1. Check for exhaust gas leaks.
  
  OK
  
  No gas leaks.
  
  Tip:
  Perform "Inspection After Repair" after repairing or replacing the exhaust system (Click here).
REPLACE HEATED OXYGEN SENSOR

(Click here)

REPAIR OR REPLACE EXHAUST GAS LEAK POINT