Dtc P0420 Catalyst System Efficiency Below Threshold (Bank 1)

Lexus IS250 IS220d GSE20 ALE20 4GR-FSE ENGINE CONTROL SYSTEM

MONITOR DESCRIPTION

CONDITIONING FOR SENSOR TESTING

INSPECTION PROCEDURE

CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0420 AND/OR P0430)

PERFORM ACTIVE TEST BY INTELLIGENT TESTER (A/F CONTROL)

CHECK FOR EXHAUST GAS LEAKAGE

DTC P0420 Catalyst System Efficiency Below Threshold (Bank 1)

DTC P0430 Catalyst System Efficiency Below Threshold (Bank 2)

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 (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 a 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 sets a DTC.

DTC No.DTC Detection ConditionTrouble Area
P0420OSC value smaller than standard value under active air-fuel ratio control (2 trip detection logic)
Gas leakage from exhaust system
A/F sensor (bank 1 sensor 1)
HO2 sensor (bank 1 sensor 2)
Exhaust manifold (TWC)
P0430OSC value smaller than standard value under active air-fuel ratio control (2 trip detection logic)
Gas leakage from exhaust system
A/F sensor (bank 2 sensor 1)
HO2 sensor (bank 2 sensor 2)
Exhaust manifold (TWC)
  • HINT:
Bank 1 refers to the bank that includes cylinder No. 1.
Bank 2 refers to the bank that does not include cylinder No. 1.
Sensor 1 refers to the sensor closest to the engine assembly.
Sensor 2 refers to the sensor farthest away from the engine assembly.

CONDITIONING FOR SENSOR TESTING

Perform the operation with the engine speeds and time durations described below prior to checking the waveforms of the A/F and HO2 sensors. This is in order to activate the sensors sufficiently to obtain the appropriate inspection results.


Dtc P0420 Catalyst System Efficiency Below Threshold (Bank 1). 4GR-FSE ENGINE CONTROL SYSTEM. Lexus IS250 IS220d GSE20 ALE20

Connect the intelligent tester to the DLC3 (Procedure "A").
Start the engine and warm it up with all the accessories switched OFF, until the engine coolant temperature stabilizes (Procedure "B").
Run the engine at engine speed of between 2,500 rpm and 3,000 rpm for at least 3 minutes (Procedure "C").
While running the engine at 3,000 rpm for 2 seconds and 2,000 rpm for 2 seconds, check the waveforms of the A/F and HO2 sensors using the tester or scan tool (Procedure "D").
  • NOTICE:
  • The Air-Fuel Ratio (A/F) sensor has an output delay of a few seconds and the Heated Oxygen (HO2) sensor has a maximum output delay of approximately 20 seconds.
CaseA/F Sensor (Sensor 1)
Output Voltage		HO2 Sensor (Sensor 2)
Output Voltage		Main Suspected Trouble Area
1Injection Volume
+25 %
-12.5 %		Dtc P0420 Catalyst System Efficiency Below Threshold (Bank 1). 4GR-FSE ENGINE CONTROL SYSTEM. Lexus IS250 IS220d GSE20 ALE20Injection Volume
+25 %
-12.5 %		Dtc P0420 Catalyst System Efficiency Below Threshold (Bank 1). 4GR-FSE ENGINE CONTROL SYSTEM. Lexus IS250 IS220d GSE20 ALE20-
Output Voltage
More than 3.35 V
Less than 3.0 V		Dtc P0420 Catalyst System Efficiency Below Threshold (Bank 1). 4GR-FSE ENGINE CONTROL SYSTEM. Lexus IS250 IS220d GSE20 ALE20Output Voltage
More than 0.55 V
Less than 0.4 V		Dtc P0420 Catalyst System Efficiency Below Threshold (Bank 1). 4GR-FSE ENGINE CONTROL SYSTEM. Lexus IS250 IS220d GSE20 ALE20
2Injection Volume
+25 %
-12.5 %		Dtc P0420 Catalyst System Efficiency Below Threshold (Bank 1). 4GR-FSE ENGINE CONTROL SYSTEM. Lexus IS250 IS220d GSE20 ALE20Injection Volume
+25 %
-12.5 %		Dtc P0420 Catalyst System Efficiency Below Threshold (Bank 1). 4GR-FSE ENGINE CONTROL SYSTEM. Lexus IS250 IS220d GSE20 ALE20
A/F sensor
A/F sensor heater
A/F sensor circuit
Output Voltage
Almost
no reaction		Dtc P0420 Catalyst System Efficiency Below Threshold (Bank 1). 4GR-FSE ENGINE CONTROL SYSTEM. Lexus IS250 IS220d GSE20 ALE20Output Voltage
More than 0.55 V
Less than 0.4 V		Dtc P0420 Catalyst System Efficiency Below Threshold (Bank 1). 4GR-FSE ENGINE CONTROL SYSTEM. Lexus IS250 IS220d GSE20 ALE20
3Injection Volume
+25 %
-12.5 %		Dtc P0420 Catalyst System Efficiency Below Threshold (Bank 1). 4GR-FSE ENGINE CONTROL SYSTEM. Lexus IS250 IS220d GSE20 ALE20Injection Volume
+25 %
-12.5 %		Dtc P0420 Catalyst System Efficiency Below Threshold (Bank 1). 4GR-FSE ENGINE CONTROL SYSTEM. Lexus IS250 IS220d GSE20 ALE20
HO2 sensor
HO2 sensor heater
HO2 sensor circuit
Output Voltage
More than 3.35 V
Less than 3.0 V		Dtc P0420 Catalyst System Efficiency Below Threshold (Bank 1). 4GR-FSE ENGINE CONTROL SYSTEM. Lexus IS250 IS220d GSE20 ALE20Output Voltage
Almost
no reaction		Dtc P0420 Catalyst System Efficiency Below Threshold (Bank 1). 4GR-FSE ENGINE CONTROL SYSTEM. Lexus IS250 IS220d GSE20 ALE20
4Injection volume
+25 %
-12.5 %		Dtc P0420 Catalyst System Efficiency Below Threshold (Bank 1). 4GR-FSE ENGINE CONTROL SYSTEM. Lexus IS250 IS220d GSE20 ALE20Injection Volume
+25 %
-12.5 %		Dtc P0420 Catalyst System Efficiency Below Threshold (Bank 1). 4GR-FSE ENGINE CONTROL SYSTEM. Lexus IS250 IS220d GSE20 ALE20
Injector
Fuel pressure
Gas leakage from exhaust system
(Air-fuel ratio extremely lean or rich)
Output Voltage
Almost
no reaction		Dtc P0420 Catalyst System Efficiency Below Threshold (Bank 1). 4GR-FSE ENGINE CONTROL SYSTEM. Lexus IS250 IS220d GSE20 ALE20Output Voltage
Almost
no reaction		Dtc P0420 Catalyst System Efficiency Below Threshold (Bank 1). 4GR-FSE ENGINE CONTROL SYSTEM. Lexus IS250 IS220d GSE20 ALE20
Following the A/F CONTROL procedure enables technicians to check and graph the output voltages of both the A/F and HO2 sensors.
To display the graph, enter the following menus on the tester: Power train / Engine / Active Test / Control the Injection Volume for A/F Sensor and Data List / AFS B1 S1 and O2S B1 S2 or AFS B2 S1 and O2S B2 S2, and press the YES button and then the ENTER button followed by the F4 button.

INSPECTION PROCEDURE

  • HINT:
  • Read freeze frame data using the intelligent tester. Freeze frame data records the engine conditions when malfunctions are detected. When troubleshooting, freeze frame data can help determine if the vehicle was running or stopped, 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 .
1.CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0420 AND/OR P0430)

Connect the intelligent tester to the DLC3.

Turn the engine switch on (IG) and turn the tester ON.

Enter the following menus: Power train / Engine / DTC.

Read DTCs.

  • Result:
  • Display (DTC output)Proceed to
    P0420 and/or P0430A
    P0420 and/or P0430 and other DTCsB
  • HINT:
  • If any DTCs other than P0420 or P0430 are output, troubleshoot those DTCs first.
B
GO TO DTC CHART
A
2.PERFORM ACTIVE TEST BY INTELLIGENT TESTER (A/F CONTROL)

Connect the intelligent tester to the DLC3.

Start the engine and turn the tester ON.

Warm up the engine at engine speed of 2,500 rpm for approximately 90 seconds.

On the tester, enter the following menus: Power train / Engine / Active Test / Control the Injection Volume for A/F Sensor.

Perform the A/F CONTROL operation with the engine in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume.)

Monitor the output voltages of the A/F and HO2 sensors (AFS B1 S1 and O2S B1 S2 or AFS B2 S1 and O2S B2 S2) displayed on the tester.

  • HINT:
The A/F CONTROL 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.
Tester Display
(Sensor)		Injection VolumeStatusVoltage
AFS B1 S1 or AFS B2 S1
(A/F)		+25 %RichLess than 3.0
AFS B1 S1 or AFS B2 S1
(A/F)		-12.5 %LeanMore than 3.35
O2S B1 S2 or O2S B2 S2
(HO2)		+25 %Rich More than 0.55
O2S B1 S2 or O2S B2 S2
(HO2)		-12.5 %LeanLess than 0.4
  • Result:
  • Status
    AFS B1 S1
    or
    AFS B2 S1    		Status
    O2S B1 S2
    or
    O2S B2 S2    		A/F Condition and A/F and
    HO2 Sensor Conditions    		MisfireMain Suspected Trouble AreasProceed to
    Lean/RichLean/RichNormal-
    Three-Way Catalytic Converter (TWC)
    Gas leakage from exhaust system
    		A
    LeanLean/RichA/F sensor malfunction-
    A/F sensor
    		B
    RichLean/RichA/F sensor malfunctionMay occur
    A/F sensor
    		B
    Lean/RichLeanHO2 sensor malfunction-
    HO2 sensor
    Gas leakage from exhaust system
    		C
    Lean/RichRichHO2 sensor malfunction-
    HO2 sensor
    Gas leakage from exhaust system
    		C
    LeanLeanActual air-fuel ratio leanMay occur
    Extremely rich or lean actual air-fuel ratio
    Gas leakage from exhaust system
    		A
    RichRichActual air-fuel ratio lean-
    Extremely rich or lean actual air-fuel ratio
    Gas leakage from exhaust system
    		A
Lean:
During A/F CONTROL, the A/F sensor (AFS) output voltage is consistently more than 3.35 V, and the HO2 sensor output voltage (O2S) is consistently less than 0.4 V.
Rich:
During A/F CONTROL, the AFS is consistently less than 3.0 V, and the O2S is consistently more than 0.55 V.
Lean/Rich:
During A/F CONTROL of the ACTIVE TEST, the output voltage of the HO2 sensor alternates correctly.
B
CHECK AND REPLACE AIR FUEL RATIO SENSOR
C
CHECK AND REPLACE HEATED OXYGEN SENSOR, AND CHECK AND REPAIR EXHAUST GAS LEAKAGE
A
3.CHECK FOR EXHAUST GAS LEAKAGE
  • OK:
  • No gas leakage.
NG
REPAIR OR REPLACE EXHAUST GAS LEAKAGE POINT
OK
REPLACE THREE-WAY CATALYTIC CONVERTER