Diagnostic Trouble Code P0420 1AZ-FE

DTC P0420 Catalyst System Efficiency Below Threshold (Bank 1)

1. Description

2. Confirmation driving pattern

3. Conditioning for sensor testing

4. Inspection procedure

5. Check any other dtcs output (in addition to dtc p0420)

Description DTC P0420

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 sets the DTC.

Toyota fault codes

DTC No.	DTC Detection Condition	Trouble Area
P0420	OSC value smaller than standard value under active air-fuel ratio control (2 trip detection logic)	Front exhaust pipe (with TWC) Gas leakage from exhaust system Air-Fuel Ratio (A/F) sensor (sensor 1) Heated Oxygen (HO2) sensor (sensor 2)

Confirmation driving pattern

HINT:

Performing this confirmation pattern will activate the catalyst monitor. This is very useful for verifying the completion of a repair.

1. (a) Connect the intelligent tester to the DLC3.
2. (b) Turn the ignition switch on (IG).
3. (c) Turn the tester ON.
4. (d) Clear DTCs (if set).
5. (e) Enter Check Mode.
6. (f) Select the following menu items: Powertrain / Engine and ECT / Utility / Monitor Status.
7. (g) Check that Catalyst is Incomplete.
8. (h) Start the engine and warm it up.
9. (i) Drive the vehicle at between 40 mph and 70 mph (64 km/h and 113 km/h) for at least 10 minutes.
10. (j) Note the state of the Readiness Tests items. Those items will change to Complete as Catalyst monitor operates.
11. (k) On the tester, select the following menu items: Powertrain / Engine and ECT / DTC.

HINT:

If Catalyst does not change to Complete, and any pending DTCs fail to set, extend the driving time.

Conditioning for sensor testing

HINT:

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.

1. (a) Connect the intelligent tester to the DLC3.
2. (b) Start the engine and warm it up with all the accessories switched OFF, until the engine coolant temperature stabilizes.
3. (c) Run the engine at an engine speed of between 2,500 rpm and 3,000 rpm for at least 3 minutes.
4. (d) While running the engine at 3,000 rpm and 2,000 rpm alternating at 2 second intervals, check the waveforms of the A/F and HO2 sensors using the tester.

HINT:

1. If either voltage output of the Air-Fuel Ratio (A/F) or Heated Oxygen (HO2) sensor does not fluctuate, or there is a noise in the waveform of either sensor, the sensor may be malfunctioning.
2. 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 following Control the Injection Volume for A/F Sensor using the intelligent tester.
3. 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 DTC P0420

HINT:

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.

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

1. Connect the intelligent tester to the DLC3.

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

3. Select the following menu items: Powertrain / Engine and ECT / DTC.

4. Read DTCs.

   Result:

   Display (DTC Output)	Proceed to
   P0420	A
   P0420 and other DTCs	B

   HINT:

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

B	GO TO DTC CHART

A

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

1. Connect the intelligent tester to the DLC3.

2. Start the engine and turn the tester ON.

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

4. On the tester, select the following menu items: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.

5. 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).

6. Monitor the voltage outputs of the A/F and HO2 sensors (AFS B1 S1 and O2S B1 S2) displayed on the tester.

   Result:

   A/F sensor reacts in accordance with increases and decreases in fuel injection volume:

   +25% = Rich output:

   Less than 3.0 V

   -12.5% = Lean output:

   More than 3.35 V

NOTICE:

The A/F sensor has an output delay of a few seconds and the HO2 sensor has a maximum output delay of approximately 20 seconds.

Case	A/F Sensor (Sensor 1) Output Voltage		HO2 Sensor (Sensor 2) Output Voltage		Main Suspected Trouble Area
1	Injection Volume +25% -12.5%		Injection Volume +25% -12.5%		Catalyst Exhaust gas leakage
	Output Voltage More than 3.35 V Less than 3.0 V		Output Voltage More than 0.5 V Less than 0.4 V
2	Injection Volume +25% -12.5%		Injection Volume +25% -12.5%		A/F sensor A/F sensor heater A/F sensor circuit
	Output Voltage Almost no reaction		Output Voltage More than 0.5 V Less than 0.4 V
3	Injection Volume +25% -12.5%		Injection Volume +25% -12.5%		HO2 sensor HO2 sensor heater HO2 sensor circuit
	Output Voltage More than 3.35 V Less than 3.0 V		Output Voltage Almost no reaction
4	Injection volume +25% -12.5%		Injection Volume +25% -12.5%		Extremely rich or lean actual air-fuel ratio Injector Fuel pressure Gas leakage from exhaust system
	Output Voltage Almost no reaction		Output Voltage Almost no reaction

1. Following the Control the Injection Volume for A/F Sensor procedure enables technicians to check and graph the voltage outputs of both the A/F and HO2 sensors.
2. To display the graph, select the following menu items on the tester: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / Enter / View / AFS B1 S1 and O2S B1 S2.

Result:

Result	Proceed to
Case 1	A
Case 2	B
Case 3	C
Case 4	D

B	REPLACE AIR FUEL RATIO SENSOR
C	Go to step 4
D	CHECK CAUSE OF EXTREMELY RICH OR LEAN ACTUAL AIR-FUEL RATIO, REPLACE FAULTY AREA AND GO TO NEXT STEP

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 (BOTH FRONT AND REAR CATALYSTS (FRONT EXHAUST PIPE))

4.CHECK FOR EXHAUST GAS LEAKAGE

OK:

No gas leakage.

NG	REPAIR OR REPLACE EXHAUST GAS LEAKAGE POINT

OK
REPLACE HEATED OXYGEN SENSOR