1Nz-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 stores 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.

DTC No.	DTC Detection Condition	Trouble Area
P0420	The oxygen storage capacity value is less than the standard value under active air fuel ratio control (2 trip detection logic).	Gas leak from exhaust system Air fuel ratio sensor (bank 1 sensor 1) Heated oxygen sensor (bank 1 sensor 2) Exhaust pipe assembly front (TWC: Front catalyst and rear catalyst)

CATALYST LOCATION

Yaris. Ncp93, 131.1Nz-Fe Engine Control.Sfi System (For Sedan).
Dtc
P0420 Catalyst System Efficiency Below Threshold (Bank 1)

Text in Illustration
*1	Exhaust Manifold Assembly	*2	Air Fuel Ratio Sensor
*3	Exhaust Pipe Assembly Front	*4	Heated Oxygen Sensor
*5	Exhaust Pipe Assembly Tail	*6	TWC: Front Catalyst
*7	TWC: Rear Catalyst	-	-

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	Approximately 30 seconds
MIL Operation	2 driving cycles
Sequence of Operation	None

TYPICAL ENABLING CONDITIONS

Monitor runs whenever following DTCs not present	P0010 (Camshaft Timing Oil Control Valve) P0011 (VVT System - Advance) P0012 (VVT System - Retard) P0016 (VVT System - Misalignment) P0031, P0032, P101D (Air Fuel Ratio Sensor Heater) P0037, P0038, P102D (Heated Oxygen Sensor Heater) P2195, P2196, P2237, P2238, P2239, P2252, P2253, P014C, P014D, P015A, P015B (Air Fuel Ratio Sensor) P0136, P0137, P0138, P0139, P0607 (Rear Oxygen Sensor) P0102, P0103 (Mass Air Flow Meter) P0115, P0117, P0118 (Engine Coolant Temperature Sensor) P0125 (Insufficient Coolant Temperature for Closed Loop Fuel Control) P0120, P0121, P0122, P0123, P0220, P0222, P0223, P2135 (Throttle Position Sensor) P0171, P0172 (Fuel System) P0301 - P0304 (Misfire) P0335 (Crankshaft Position Sensor) P0340 (Camshaft Position Sensor) P0351 - P0354 (Igniter) P0500 (Vehicle Speed Sensor)
Battery voltage	11 V or higher
Intake air temperature	-10°C (14°F) or higher
Engine coolant temperature	75°C (167°F) or higher
Atmospheric pressure	76 kPa(abs) [570 mmHg(abs)] or higher
Idling	OFF
Engine speed	Less than 4000 rpm
Air fuel ratio sensor status	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	1.3 to 40 gm/sec
2. Front catalyst temperature (estimated)	620 to 805°C (1148 to 1481°F): for Automatic Transaxle 590 to 800°C (1094 to 1472°F): for Manual Transaxle
3. Rear catalyst temperature (estimated)	480 to 750°C (896 to 1382°F): for Automatic Transaxle 470 to 750°C (878 to 1382°F): for Manual Transaxle
Shift position	3rd or higher

TYPICAL MALFUNCTION THRESHOLDS

Oxygen Storage Capacity (OSC) of Three-Way Catalytic Converter (TWC)

Less than 0.10742 g

MONITOR RESULT

Refer to detailed information in Checking Monitor Status (YARIS_NCP93 RM000000PDR0B4X.html).

P0420: Catalyst Efficiency / O2 STORAGE B1
Monitor ID	Test ID	Scaling	Unit	Description
$21	$A9	Multiply by 0.0003	No dimension	Oxygen storage capacity of catalyst bank 1

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 DTCs (even if no DTCs are stored, perform the clear DTC operation).
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 (38 mph) for 10 minutes or more [B].
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 [C].
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
Check if any DTCs (pending DTCs) are stored.
HINT:
If the monitor 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 63 mph) for 10 minutes or more [D].
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 [E].
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
Check if any DTCs (pending DTCs) are stored.
HINT:
If Catalyst 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 (YARIS_NCP93 RM000000PDK0T5X.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:

Sensor 1 refers to the sensor closest to the engine assembly.
Sensor 2 refers to the sensor farthest away from the engine assembly.
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 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)

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
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.

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

GO TO DTC CHART (YARIS_NCP93 RM000000PDF0EWX.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.

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 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, 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 PIPE ASSEMBLY FRONT (TWC: FRONT CATALYST AND REAR CATALYST)

HINT:

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

Replace the exhaust pipe assembly front (TWC: front catalyst and rear catalyst) (YARIS_NCP93 RM000002WUZ00KX.html).

END

5.REPLACE AIR FUEL RATIO SENSOR (BANK 1 SENSOR 1)

Replace the air fuel ratio sensor (bank 1 sensor 1) (YARIS_NCP93 RM000003VIL00HX.html).
HINT:
Perform "Inspection After Repair" after replacing the air fuel ratio sensor (YARIS_NCP93 RM000004NJD006X.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 (BANK 1 SENSOR 2)

Replace the heated oxygen sensor (bank 1 sensor 2) (YARIS_NCP93 RM000003VIP00IX.html).

Go to step 11

8.CHECK FOR EXHAUST GAS LEAK

Check the 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 (YARIS_NCP93 RM000000WC30JKX_07.html).

Go to step 11

10.REPAIR OR REPLACE EXHAUST GAS LEAK POINT

Repair or replace exhaust gas leak point (YARIS_NCP93 RM000002WV200NX.html).
HINT:
Perform "Inspection After Repair" after repairing or replacing the exhaust system (YARIS_NCP93 RM000004NJD006X.html).

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 (YARIS_NCP93 RM000000PDK0T5X.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 DTCs.
Result
Result
Proceed to
DTC P0420 is output
A
DTC is not output
(No pending DTCs output)
B

END

A

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

HINT:

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

Replace the exhaust assembly front (TWC: front catalyst and rear catalyst) (YARIS_NCP93 RM000002WUZ00KX.html).

END