2Az-Fe Engine Control. Dtc P0420 Catalyst System Efficiency Below Threshold (Bank 1)

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 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 20 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, the ECM illuminates the MIL and stored 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 leak from exhaust system Air fuel ratio sensor (sensor 1) Heated oxygen sensor (sensor 2) Exhaust manifold converter sub-assembly (TWC: Front catalyst) and center exhaust pipe assembly (TWC: Rear catalyst)

CATALYST LOCATION

Corolla. Zre142 Aze141.2Az-Fe Engine Control.Sfi System.
Dtc
P0420 Catalyst System Efficiency Below Threshold (Bank 1)

NOTICE:

Replace the exhaust manifold converter sub-assembly and the center exhaust pipe assembly together when catalyst replacement is necessary. (Excluding air fuel ratio sensor and heated oxygen sensor)

MONITOR STRATEGY

Related DTCs	P0420: Catalyst Deterioration
Required Sensors/Components (Main)	Air fuel ratio sensor Heated oxygen sensor
Required Sensors/Components (Related)	Intake air temperature sensor Mass air flow meter Crankshaft position sensor Engine coolant temperature sensor
Frequency of Operation	Once per driving cycle
Duration	About 30 seconds
MIL Operation	2 driving cycles
Sequence of Operation	None

TYPICAL ENABLING CONDITIONS

Monitor runs whenever following DTCs are not present	P0010 (VVT Oil Control Valve) P0011 (VVT System - Advance) P0012 (VVT System - Retard) P0016 (VVT System - Misalignment) P0031, P0032 (Air Fuel Ratio Sensor Heater - Sensor 1) P0037, P0038 (Heated Oxygen Sensor Heater - Sensor 2) P0102, P0103 (Mass Air Flow Meter) P0115, P0117, P0118 (Engine Coolant Temperature Sensor) P0120, P0121 P0122, P0123, P0220, P0222, P0223, P2135 (Throttle Position Sensor) P0125 (Insufficient Engine Coolant Temperature for Closed Loop Fuel Control) P0136, P0137, P0138, P0139 (Oxygen Sensor - Sensor 2) P014C, P014D, P015A, P015B, P2195, P2196, P2237, P2238, P2239, P2252, P2253 (Air Fuel Ratio Sensor - Sensor 1) P0171, P0172 (Fuel System) P0301, P0302, P0303, P0304 (Misfire) P0335 (Crankshaft Position Sensor) P0340 (Camshaft Position Sensor) P0351, P0352, P0353, P0354 (Igniter) P0500 (Vehicle Speed Sensor) P0607 (Heated Oxygen Sensor - Sensor 2)
Battery voltage	11 V or more
Intake air temperature	-10°C (14°F) or more
Engine coolant temperature	75°C (167°F) or more
Atmospheric pressure	76 kPa (570 mmHg) or more
Idle	Off
Engine speed	Less than 4000 rpm
Air fuel ratio sensor	Activated
Fuel system status	Closed loop
Engine load	10 to 80%
All of the following conditions are met	Condition 1, 2 and 3
1. Mass air flow rate	2.5 to 50 g/sec
2. Front catalyst temperature (estimated)	620 to 840°C (1148 to 1544°F)
3. Rear catalyst temperature (estimated)	400 to 770°C (752 to 1418°F)
Shift position	Automatic transaxle models: 4th or higher Manual transaxle models: 3rd or higher

TYPICAL MALFUNCTION THRESHOLDS

Oxygen storage capacity of three-way catalytic converter

Less than 0.07 g

MONITOR RESULT

Refer to Checking Monitor Status (Link).

CONFIRMATION DRIVING PATTERN

HINT:

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

Connect the Techstream to the DLC3.
Turn the ignition switch to ON.
Turn the Techstream on.
Clear the DTCs (even if no DTCs are stored, perform the clear DTC procedure).
Turn the ignition switch off and wait for at least 30 seconds.
Turn the ignition switch to ON and turn the Techstream on.
Enter the following menus: Powertrain / Engine and ECT / Monitor / Current Monitor.
Check that Catalyst Efficiency / Current is Incomplete.
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.
HINT:
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 Techstream 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.
HINT:
1. Drive the vehicle while keeping the engine load as constant as possible.
2. The monitor item change to Complete as the Catalyst Efficiency monitor operates.
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes [F].
Check if any DTCs (pending DTCs) are stored.
HINT:
If the monitor item does not change to Complete, and no pending DTCs are stored, 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.
HINT:
1. Drive the vehicle while keeping the engine load as constant as possible.
2. The monitor item will change to Complete as the Catalyst Efficiency monitor operates.
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes [H].
Check if any DTCs (pending DTCs) are stored.
HINT:
If the monitor item does not change to Complete, and no pending DTCs are stored, extend the driving time.
If no pending DTC is output, perform a universal trip and check for permanent DTCs (COROLLA_ZRE142 RM000000PDK0ZBX.html).
HINT:
1. If a permanent DTC is output, the system is malfunctioning.
2. If no permanent DTC is output, the system is normal.

CONDITIONING FOR SENSOR TESTING

HINT:

Perform the operation with the engine speeds and time durations described below prior to checking the waveforms of the air fuel ratio and heated oxygen sensors. This is to activate the sensors sufficiently to obtain appropriate inspection results.

(a) Connect the Techstream 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 for 2 seconds, and then 2000 rpm for 2 seconds, check the waveforms of the air fuel ratio and heated oxygen sensors using the Techstream.

HINT:

If the voltage output of either the air fuel ratio or heated oxygen 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, perform the Control the Injection Volume Active Test using the Techstream.
If the Three-way Catalytic Converter (TWC) has deteriorated, the heated oxygen sensor (located behind the Three-way Catalytic Converter [TWC]) voltage output fluctuates up and down frequently, even under normal driving conditions (active air fuel ratio control is not performed).

INSPECTION PROCEDURE

HINT:

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 Techstream. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.
Sensor 1 refers to the sensor closest to the engine assembly.
Sensor 2 refers to the sensor farthest away from the engine assembly.

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

Connect the Techstream to the DLC3.

Turn the ignition switch to ON.

Turn the Techstream on.

Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

Read DTCs.

Result:

Result
Proceed to
P0420
A
P0420 and other DTCs
B
HINT:
If any DTCs other than P0420 are output, troubleshoot those DTCs first.

GO TO DTC CHART (COROLLA_ZRE142 RM000000PDF0G9X.html)

A

2.PERFORM ACTIVE TEST USING TECHSTREAM (CONTROL INJECTION VOLUME)

Connect the Techstream to the DLC3.

Start the engine and warm it up.

Turn the Techstream on.

Run 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 / GAS AF Control / AFS Voltage B1S1 and O2S B1S2.

Perform the Active Test operation with the engine idling (press the RIGHT or LEFT button to change the fuel injection volume).

Monitor the voltage outputs of the air fuel ratio sensor and heated oxygen sensor (AFS Voltage B1S1 and O2S B1S2) displayed on the Techstream.

HINT:

Change the fuel injection volume within the range of - 12% to +12%. The injection volume can be changed in fine gradations.
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:

Techstream Display (Sensor)	Injection Volume	Status	Voltage
AFS Voltage B1S1 (Air fuel ratio)	+12%	Rich	Below 3.1 V
AFS Voltage B1S1 (Air fuel ratio)	-12%	Lean	Higher than 3.4 V
O2S B1S2 (Heated oxygen)	+12%	Rich	Higher than 0.55 V
O2S B1S2 (Heated oxygen)	-12%	Lean	Below 0.4 V

Result
Status AFS Voltage B1S1	Status O2S B1S2	Actual air fuel ratio, air fuel ratio sensor and heated oxygen sensor condition	Misfire	Main Suspected Trouble Area	Proceed to
Lean/Rich	Lean/Rich	Normal	-	Three-way catalytic converter Gas leak 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 leak from exhaust system	C
Lean/Rich	Rich	Heated oxygen sensor malfunction	-	Heated oxygen sensor Gas leak from exhaust system	C
Lean	Lean	Actual air fuel ratio lean	May occur	Extremely lean actual air fuel ratio Gas leak from exhaust system	D
Rich	Rich	Actual air fuel ratio rich	-	Extremely rich actual air fuel ratio Gas leak from exhaust system	D

Lean: During Control the Injection Volume, 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 Control the Injection Volume, the AFS Voltage B1S1 is consistently below 3.1 V, and the O2S B1S2 is consistently higher than 0.55 V.
Lean/Rich: During Control the Injection Volume of the Active Test, the output voltage of the air fuel ratio sensor and heated oxygen sensor alternate correctly.

Go to step 5

Go to step 6

Go to step 8

A

3.CHECK FOR EXHAUST GAS LEAK

Check for exhaust gas leaks.

OK:: No gas leaks.

Go to step 10

OK

4.REPLACE EXHAUST MANIFOLD CONVERTER SUB-ASSEMBLY (TWC: FRONT CATALYST) AND CENTER EXHAUST PIPE ASSEMBLY (TWC: REAR CATALYST)

NOTICE:

Replace the exhaust manifold converter sub-assembly (TWC: Front catalyst) and the center exhaust pipe assembly (TWC: Rear catalyst) together when catalyst replacement is necessary.

HINT:

Confirm the replacement parts, referring to the illustration in the Catalyst Location.

Replace the exhaust manifold converter sub-assembly (TWC: Front catalyst) (COROLLA_ZRE142 RM000002CR300BX.html).

Replace the center exhaust pipe assembly (TWC: Rear catalyst) (COROLLA_ZRE142 RM000002WV003NX.html).

END

5.REPLACE AIR FUEL RATIO SENSOR

Replace the air fuel ratio sensor (COROLLA_ZRE142 RM0000033D700IX.html).

Go to step 11

6.CHECK FOR EXHAUST GAS LEAK

Check for exhaust gas leaks.

OK:: No gas leaks.

Go to step 10

OK

7.REPLACE HEATED OXYGEN SENSOR

Replace the heated oxygen sensor (COROLLA_ZRE142 RM0000033D300QX.html).

Go to step 11

8.CHECK FOR EXHAUST GAS LEAK

Check for exhaust gas leaks.

OK:: No gas leaks.

Go to step 10

OK

9.CHECK CAUSE OF EXTREMELY RICH OR LEAN ACTUAL AIR FUEL RATIO

Check the cause of extremely rich or lean actual air fuel ratio, referring to the DTC P0171 Inspection Procedure (COROLLA_ZRE142 RM000000WC30N4X.html).

Go to step 11

10.REPAIR OR REPLACE EXHAUST GAS LEAK POINT

Repair or replace exhaust gas leak point.

NEXT

11.CHECK WHETHER DTC OUTPUT RECURS (DTC P0420)

Connect the Techstream to the DLC3.

Turn the ignition switch to ON.

Turn the Techstream on.

Clear the DTCs (COROLLA_ZRE142 RM000000PDK0ZBX.html).

Turn the ignition switch off and wait for at least 30 seconds.

Turn the ignition switch to ON.

Turn the Techstream on.

Start the engine.

Drive the vehicle in accordance with the driving pattern described in Confirmation Driving Pattern.

Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

Read the DTCs.

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

END

A

12.REPLACE EXHAUST MANIFOLD CONVERTER SUB-ASSEMBLY (TWC: FRONT CATALYST) AND CENTER EXHAUST PIPE ASSEMBLY (TWC: REAR CATALYST)

NOTICE:

Replace the exhaust manifold converter sub-assembly (TWC: Front catalyst) and the center exhaust pipe assembly (TWC: Rear catalyst) together when catalyst replacement is necessary.

HINT:

Confirm the replacement parts, referring to the illustration in the Catalyst Location.

Replace the exhaust manifold converter sub-assembly (TWC: Front catalyst) (COROLLA_ZRE142 RM000002CR300BX.html).

Replace the center exhaust pipe assembly (TWC: Rear catalyst) (COROLLA_ZRE142 RM000002WV003NX.html).

END

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