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.

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.

Text in Illustration
*1	Exhaust Manifold	*2	Front Exhaust Pipe Assembly (TWC: Front Catalyst and Rear Catalyst)
*3	Tail Exhaust Pipe Assembly	-	-

DTC No.	DTC Detection Condition	Trouble Area
P0420	The Oxygen Storage Capacity (OSC) value is smaller 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)

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.

(a) Connect the intelligent tester to the DLC3.
(b) Turn the ignition switch to ON and turn the intelligent tester on.
(c) Enter the following menus: Powertrain / Engine and ECT / DTC / Clear.
(d) Clear DTCs (if output).
(e) Enter the following menus: Powertrain / Engine and ECT / Data List / Catalyst Monitor.
(f) Check that Catalyst Monitor is INCMPL (incomplete).
(g) Start the engine and warm it up.
(h) Drive the vehicle at between 64 km/h and 113 km/h (40 mph and 70 mph) for at least 10 minutes.
(i) The monitor items will change to COMPL (Complete) as Catalyst Monitor operates.
(j) Enter the following menus: Powertrain / Engine / DTC / Pending; and then check if any DTCs (any pending DTCs) are output.

Tech Tips

If Catalyst Monitor does not change to Compl (Complete), and no pending DTCs are stored, extend the driving time.

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 (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 intelligent tester 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 tester.

Tech Tips

If either voltage output of the A/F or HO2 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 sensors remain lean or rich, the air fuel ratio may be extremely lean or rich. In such cases, enter the following menus: Powertrain / Engine / 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).

INSPECTION PROCEDURE

Tech Tips

Read freeze frame data using the intelligent tester. 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.

PROCEDURE

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

Connect the intelligent tester to the DLC3.
Turn the ignition switch to ON and turn the tester on.
Enter the following menus: Powertrain / Engine and ECT / DTC.

Read 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 (INJECTION VOLUME CONTROL)

Connect the intelligent tester to the DLC3.
Start the engine and turn the tester on.
Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.
Enter the following menus: Powertrain / Engine / Active Test / Control the Injection Volume for A/F sensor.
Perform the Control the Injection Volume for A/F sensor operation with the engine idling (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 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 25%.

Each sensor reacts in accordance with increases and decreases in the fuel injection volume.

Standard

Tester Display (Sensor)	Injection Volume	Status	Voltage
AFS Voltage B1S1 (A/F)	+25%	Rich	Below 3.1 V
AFS Voltage B1S1 (A/F)	-12.5%	Lean	Higher than 3.4 V
O2S B1S2 (HO2)	+25%	Rich	Higher than 0.55 V
O2S B1S2 (HO2)	-12.5%	Lean	Below 0.4 V

Result
Status AFS Voltage B1S1	Status O2S B1S2	A/F Condition and A/F and HO2 Sensors Conditions	Misfires	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	May occur	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 voltage is consistently below 3.1 V, and the O2S voltage 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.

REPLACE AIR FUEL RATIO SENSOR Click here

INSPECT FOR EXHAUST GAS LEAK Click here

CHECK EXTREMELY RICH OR LEAN ACTUAL AIR FUEL RATIO, REPAIR CAUSE AND GO TO STEP 3 Click here

INSPECT FOR EXHAUST GAS LEAK
1. Inspect for exhaust gas leakage.
  
  OK
  
  No gas leakage.
NG
REPAIR OR REPLACE EXHAUST GAS LEAK POINT

OK
REPLACE FRONT EXHAUST PIPE ASSEMBLY (TWC: FRONT CATALYST AND REAR CATALYST)
1. Replace the front exhaust pipe assembly Click here.
NEXT

OK
No gas leakage.

CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED

Tech Tips

Immediately after replacing the Three Way Catalytic Converter (TWC) with a new one, drive the vehicle as specified below and check that Pending DTC P0420, P0136, P0137 and P0138 are not output. If any of these DTCs are output after driving the vehicle, perform the same driving pattern again.

Connect the intelligent tester to the DLC3.
Turn the ignition switch to ON and turn the tester on.
Clear the DTCs Click here.
Drive the vehicle at between 64 km/h and 113 km/h (40 mph and 70 mph) for at least 10 minutes.
Enter the following menus: Powertrain / Engine / DTC.

Read the DTCs (Pending DTCs).

Result
Result	Proceed to
Pending DTC P0136, P0137, P0138 or P0420 is output	A
Pending DTC is not output	B

END

CHECK WHETHER DTC OUTPUT RECURS
1. Connect the intelligent tester to the DLC3.
2. Turn the ignition switch to ON and turn the tester on.
3. Clear the DTCs Click here.
4. Drive the vehicle at between 64 km/h and 113 km/h (40 mph and 70 mph) for at least 10 minutes.
5. Enter the following menus: Powertrain / Engine / DTC.
6. Read the DTCs (Pending DTCs).
  
  Result
  
  Pending DTC is not output
NEXT

END
INSPECT FOR EXHAUST GAS LEAK
1. Inspect for exhaust gas leakage.
  
  OK
  
  No gas leakage.
NG
REPAIR OR REPLACE EXHAUST GAS LEAK POINT

OK

REPLACE HEATED OXYGEN SENSOR Click here