DTC P0420: Catalyst System Efficiency Below Threshold Bank 1: Notes

DTC detecting condition:

Detected when two consecutive driving cycles with fault occur.

Trouble symptom:

Engine stall
Idle mixture is out of specifications

NOTE: After the faulty parts are repaired or replaced, perform the final check in Basic Diagnostic Procedure. Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>BASIC DIAGNOSTIC PROCEDURE>PROCEDURE .

CHECK DTC .
1. Turn the ignition switch to ON.
2. Read the DTC of [Engine] using the Subaru Select Monitor. Ref. to COMMON (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC) .
Besides DTC P0420, is any of the following DTCs displayed?

DTC P0030, P0031, P0032

DTC P0037, P0038

DTC P0131, P0132, P0134, P0137, P0138

DTC P0140, P0141

DTC P014C, P014D, P015A, P015B

DTC P0171, P0172

DTC P0300, P0301, P0302, P0303, P0304

Yes: Check the appropriate DTC using the "Diagnostic Trouble Code (DTC)". Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>DIAGNOSTIC TROUBLE CODE (DTC)>LIST .

No: Go to 2.
CHECK ENGINE OIL CONSUMPTION .
1. Turn the ignition switch to OFF.
2. Check the engine oil amount. Ref. to LUBRICATION (H4DOTC)>ENGINE OIL .
3. Start the engine and check for white smoke emitted from the muffler.
Is white smoke emitted from the muffler?

Yes: Check the engine, and repair the defective part. Ref. to MECHANICAL (H4DOTC)>SYMPTOMS AND CAUSES .

After repairing the engine, replace all the catalytic converters.

Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DOTC)>FRONT CATALYTIC CONVERTER .

Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DOTC)>REAR CATALYTIC CONVERTER .

After replacement, go to 5.

No: Go to 3.
CHECK EGR SYSTEM .
Check for leakage in the pipes consisting of the EGR system.

Check the following items regarding exhaust system.
- Loose or detached nut and bolt
- Exhaust gas leakage
- Air suction
- Hole on exhaust pipe
Is the check result OK?

Yes: Go to 4.

No: Repair or replace faulty parts. Ref. to EXHAUST(H4DOTC)>GENERAL DESCRIPTION .

After operation, go to 6.

PERFORM ACTIVE TEST .

Check the following items regarding exhaust system.

Start and warm up the engine.
Using the Subaru Select Monitor, select [Injection Quantity Control] of [Active Test].
NOTE: For detailed operation procedures, refer to "Help" of application.

Check [A/F Sensor #1] when the injector injection amount is increased or decreased.

At normal condition

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(1) When increased by 5%

(2) When increased by 10%

(3) When increased by 15%

(4) When increased by 20%

In malfunction

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(1) When increased by 5%

(2) When increased by 10%

(3) When increased by 15%

(4) When increased by 20%

Does [A/F Sensor #1] change according to changes in the injector injection amount?

Yes: Replace all the catalytic converters.

Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DOTC)>FRONT CATALYTIC CONVERTER .

Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DOTC)>REAR CATALYTIC CONVERTER .

After replacement, go to 5.

No: Replace the front oxygen (A/F) sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>FRONT OXYGEN (A/F) SENSOR .

After replacement, go to 6.

PERFORM DRIVING TEST
1. Perform the inspection mode V. Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>INSPECTION MODE .
  WARNING: When performing inspection mode on a public road, pay sufficient attention to the traffic condition and give the highest priority to safe driving.
2. Using the Subaru Select Monitor, read the values in [Catalyst deterioration diagnosis] according to the reading out procedure of MODE $06. Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>GENERAL SCAN TOOL .
3. Record the readings [Catalyst deterioration diagnosis].
Is the value greater than or equal to the following value?

0.7 g (0.025 oz)

Yes: Finish the diagnosis.

No: Go to 7.
PERFORM DRIVING TEST .
1. Perform the inspection mode V. Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>INSPECTION MODE .
  WARNING: When performing inspection mode on a public road, pay sufficient attention to the traffic condition and give the highest priority to safe driving.
2. Using the Subaru Select Monitor, read the values in [Catalyst deterioration diagnosis] according to the reading out procedure of MODE $06. Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>GENERAL SCAN TOOL .
3. Record the readings [Catalyst deterioration diagnosis].
Is the value greater than or equal to the following value?
- CVT model: 0.15 g (0.005 oz)
- MT model: 0.25 g (0.009 oz)
Yes: Finish the diagnosis.

No: Replace all the catalytic converters.

Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DOTC)>FRONT CATALYTIC CONVERTER .

Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DOTC)>REAR CATALYTIC CONVERTER .

After replacement, go to 5.
CHECK EGR SYSTEM .
NOTE: Check for leakage in the pipes consisting of the EGR system.
NOTE:
Check the following items.
- Looseness of each flange connection
- Improper installation of the electronic throttle control
- Improper installation of manifold absolute pressure and intake air temperature sensor
- Foreign matter adhering to EGR control valve
Is the check result OK?

Yes: Go to 8.

No: Repair or replace faulty parts.

CHECK WAVEFORM .

Start the engine and warm up completely.
Read the waveform data of rear oxygen sensor during idling using an oscilloscope.

Check the waveform by waggling the connector between ECM and rear oxygen sensor.

At normal condition

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At abnormal condition 2 (noise input)

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Is an abnormal waveform displayed?

Yes: Check the contact point of the connector that caused disturbed waveform. If faulty, repair or replace it.

No: As it is possible that a temporary poor contact or minor failure occurs in the connector, perform the diagnosis again according to the basic diagnostic procedure.

NOTE: If the catalyst has already been replaced, do not replace it.