2Zr-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 leaks from exhaust system Air fuel ratio sensor (sensor 1) Heated oxygen sensor (sensor 2) Front exhaust pipe assembly (TWC: Front and rear catalyst)

CATALYST LOCATION

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

NOTICE:

When replacing the front exhaust pipe assembly in order to replace the three-way catalytic converter, it is not necessary to replace the 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 not present	P0010 (VVT Oil Control Valve) P0011 (VVT System - Advance) P0012 (VVT System - Retard) P0013 (Exhaust VVT Oil Control Valve) P0014 (Exhaust VVT System - Advance) P0015 (Exhaust VVT System - Retard) P0016 (VVT System - Misalignment) P0017 (Exhaust 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 (Rear Oxygen sensor - Sensor 2) P0171, P0172 (Fuel System) P0301, P0302, P0303, P0304 (Misfire) P0335 (Crankshaft Position Sensor) P0340, P0342, P0343 (Camshaft Position Sensor) P0351, P0352, P0353, P0354 (Igniter) P0365, P0367, P0368 (Exhaust Camshaft Position Sensor) P0500 (Vehicle Speed Sensor) P0607 (Heated Oxygen Sensor - Sensor 2) P2195, P2196, P2237, P2238, P2239, P2252, P2253, P2A00 (Air Fuel Ratio Sensor - Sensor 1) P219A (Air Fuel Ratio Imbalance)
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(abs) [570 mmHg(abs)] or more
Idling	Off
Engine speed	Less than 4000 rpm
Air fuel ratio sensor status	Activated
Fuel system status	Closed loop
Engine load	10% or more, and less than 80%
All of the following conditions are met	Condition 1, 2 and 3
1. Mass air flow rate	2.5 gm/sec or more, and less than 50 gm/sec
2. Front catalyst temperature (estimated)	655°C (1211°F) or more, and less than 860°C (1580°F) (Automatic Transaxle models) 675°C (1247°F) or more, and less than 860°C (1580°F) (Manual Transaxle models)
3. Rear catalyst temperature (estimated)	400°C (752°F) or more, and less than 760°C (1400°F)
Heated oxygen sensor monitor	Completed
Shift position	4th or more

TYPICAL MALFUNCTION THRESHOLDS

Oxygen Storage Capacity (OSC) of catalyst

Less than 0.068 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 RM000000PDK0ZAX.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 sensor and heated oxygen sensor. This is in order to activate the sensors sufficiently to obtain the 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 2000 rpm for 2 seconds, check the waveforms of the air fuel ratio and heated oxygen sensors using the Techstream.

HINT:

If either of the voltage outputs of the air fuel ratio or heated oxygen 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 the sensors remain lean or rich, the air fuel ratio may be extremely lean or rich. In such cases, perform the following menu items: Powertrain / Engine and ECT / Active Test / Control the Injection Volume.
If the three-way catalytic converter has deteriorated, the heated oxygen sensor (located behind the three-way catalytic converter) 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 the DTCs.

Result:

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

GO TO DTC CHART (COROLLA_ZRE142 RM000000PDF0G8X.html)

A

2.PERFORM ACTIVE TEST USING TECHSTREAM (CONTROL THE 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 / All Data / AFS Voltage B1S1 and O2S B1S2.

Perform the Active Test 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 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 there is almost no response from the air fuel ratio sensor, a malfunction of the air fuel ratio sensor is suspected.

Standard:

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

Result:

Status AFS Voltage B1S1	Status O2S B1S2	Air Fuel Ratio Condition and Air Fuel Ratio and Heated Oxygen Sensors Condition	Misfire	Main Suspected Trouble Area	Proceed to
Lean/Rich	Lean/Rich	Normal	-	Three-way catalytic converter Gas leakage 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 leakage from exhaust system	C
Lean/Rich	Rich	Heated oxygen sensor malfunction	-	Heated oxygen sensor Gas leakage from exhaust system	C
Lean	Lean	Actual air fuel ratio lean	May occur	Extremely rich or lean actual air fuel ratio Gas leakage from exhaust system	D
Rich	Rich	Actual air fuel ratio rich	-	Extremely rich or lean actual air fuel ratio Gas leakage from exhaust system	D

Lean: During Control the Injection Volume, the air fuel ratio sensor output voltage (AFS Voltage) is consistently more than 3.4 V, and the heated oxygen sensor output voltage (O2S) is consistently less than 0.4 V.
Rich: During the AFS Voltage is consistently less than 3.1 V, and the O2S is consistently more than 0.55 V.
Lean/Rich: During Control the Injection Volume of the Active Test, the output voltage of the heated oxygen sensor alternates 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 FRONT EXHAUST PIPE ASSEMBLY (TWC: FRONT AND REAR CATALYST)

NOTICE:

When replacing the front exhaust pipe assembly in order to replace the three-way catalytic converter, it is not necessary to replace the heated oxygen sensor.

HINT:

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

Replace the front exhaust pipe assembly (TWC: Front and rear catalyst) (COROLLA_ZRE142 RM000002WV003MX.html).

END

5.REPLACE AIR FUEL RATIO SENSOR (SENSOR 1)

Replace the air fuel ratio sensor (COROLLA_ZRE142 RM00000306S01AX.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 OXYGEN SENSOR (SENSOR 2)

Replace the heated oxygen sensor (COROLLA_ZRE142 RM00000306V015X.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 case of extremely rich or lean actual air fuel ratio, referring to the DTC P0171 Inspection Procedure (COROLLA_ZRE142 RM000000WC30N3X_07.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 RM000000PDK0ZAX.html).

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

Drive the vehicle in accordance with the driving pattern described in the 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
(Pending DTC is not output)
B

END

A

12.REPLACE FRONT EXHAUST PIPE ASSEMBLY (TWC: FRONT AND REAR CATALYST)

NOTICE:

When replacing the front exhaust pipe assembly in order to replace the three-way catalytic converter, it is not necessary to replace the heated oxygen sensor.

HINT:

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

Replace the front exhaust pipe assembly (TWC: Front and rear catalyst) (COROLLA_ZRE142 RM000002WV003MX.html).

END

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