DTC P0420: Catalyst System Efficiency Below Threshold Bank 1: Notes
1. -
DTC detecting condition:
Detected when two consecutive driving cycles with fault occur.
Trouble symptom:
- Engine stall
- Idle mixture is out of specifications
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 AND FREEZE FRAME DATA
.
- Turn the ignition switch to ON.
- Using the Subaru Select Monitor or a general scan tool, read the DTC of [Engine]. Ref. to COMMON (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC)
- Read the freeze frame data.NOTE:
For detailed operation procedures, refer to "COMMON (DIAGNOSTICS)". Ref. to COMMON (DIAGNOSTICS)>FREEZE FRAME DATA
- Save the displayed DTC and freeze frame data.
Is DTC other than P0420 displayed? (Current code)
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
.
Check the engine oil amount. Ref. to LUBRICATION (H4DOTC)>ENGINE OIL
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
No : Go to 3.
- CHECK EGR SYSTEM
.
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 4.
No : Repair or replace faulty parts.
- CHECK EXHAUST SYSTEM
.
Check the following items regarding exhaust system.
- Loose or detached nut and bolt
- Exhaust gas leakage
- Air suction
- Hole on exhaust pipe
Is there any trouble?
Yes : Repair or replace the exhaust system. Ref. to EXHAUST (H4DOTC)>GENERAL DESCRIPTION
No : Go to 5.
- CHECK FRONT OXYGEN (A/F) SENSOR
.
Visually check the front oxygen (A/F) sensor and the vicinity of front oxygen (A/F) sensor.
Is there any trace of oil on the front oxygen (A/F) sensor or in the vicinity of the front oxygen (A/F) sensor?
Yes : Go to 6.
No : Go to 7.
- CHECK FRONT OXYGEN (A/F) SENSOR
.
- Start the engine and warm up completely.
- Using the Subaru Select Monitor, decelerate by accelerator OFF from driving at a constant speed of 60 km/h (37.3 MPH), and read the waveform data of [A/F Sensor #1] and [Target Equivalence Ratio] while the vehicle is stopped.
Is an abnormal waveform displayed?
Yes : Replace the front oxygen (A/F) sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>FRONT OXYGEN (A/F) SENSOR
No : Go to 7.
- CHECK CATALYTIC CONVERTER
.
- 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.
Is an abnormal waveform displayed?
Yes : Connect the connector after checking the following items, and check the waveform again while waggling.
- Check the contact point of the connector that caused disturbed waveform. If faulty, repair or replace it.
- If any problem is not found, it is possible that a temporary poor contact occurs in the connector.
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