Subaru Crosstrek Service Manual: Dtc p0420 catalyst system efficiency below threshold bank 1

Subaru Crosstrek Service Manual / Engine (diagnostics)(h4do) / Diagnostic procedure with diagnostic trouble code (dtc) / Dtc p0420 catalyst system efficiency below threshold bank 1

ENGINE (DIAGNOSTICS)(H4DO) > Diagnostic Procedure with Diagnostic Trouble Code (DTC)

DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD BANK 1

DTC detecting condition:

Detected when two consecutive driving cycles with fault occur.

Trouble symptom:

• Engine stall

• Idle mixture is out of specifications

CAUTION:

After servicing or replacing faulty parts, perform Clear Memory Mode Clear Memory Mode > OPERATION">, and Inspection Mode Inspection Mode > PROCEDURE">.

Wiring diagram:

Engine electrical system Engine Electrical System">

STEP	CHECK	YES	NO

1.CHECK EXHAUST SYSTEM.

Check for gas leaks or air suction caused by loose or dislocated nuts and bolts, and open hole at exhaust pipes.

NOTE:

Check the following positions.

• Between cylinder head and front exhaust pipe

• Between front exhaust pipe and front catalytic converter

• Between front catalytic converter and rear catalytic converter

• Loose or improperly attached front oxygen (A/F) sensor or rear oxygen sensor

Is there any fault in exhaust system?

Repair or replace the exhaust system. General Description">

Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD BANK 1">Go to Step 2.

2.CHECK WAVEFORM DATA ON THE SUBARU SELECT MONITOR (WHILE DRIVING).

1) Drive at a constant speed between 80 — 112 km/h (50 — 70 MPH).

2) After 5 minutes have elapsed in the condition of step 1), use the Subaru Select Monitor while still driving to read the waveform data.

• At normal condition

• At abnormal condition (numerous inversion)

Is a normal waveform displayed?

Even if DTC is detected, the circuit has returned to a normal condition at this time. Reproduce the failure, and then perform the diagnosis again.

NOTE:

In this case, temporary poor contact of connector, temporary open or short circuit of harness may be the cause.

Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD BANK 1">Go to Step 3.

3.CHECK WAVEFORM DATA ON THE SUBARU SELECT MONITOR (WHILE IDLING).

1) Run the engine at idle.

2) In the condition of step 1), use the Subaru Select Monitor to read the waveform data.

• At normal condition

• At abnormal condition 1 (numerous inversion)

• At abnormal condition 2 (noise input)

Is a normal waveform displayed?

Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD BANK 1">Go to Step 4.

• The waveform is displayed at abnormal condition 1: Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD BANK 1">Go to Step 4.

• The waveform is displayed at abnormal condition 2: Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD BANK 1">Go to Step 5.

4.CHECK CATALYTIC CONVERTER.

Is the catalytic converter damaged?

Replace the catalytic converter. Front Catalytic Converter"> Rear Catalytic Converter">

Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD BANK 1">Go to Step 5.

5.CHECK REAR OXYGEN SENSOR CONNECTOR AND COUPLING CONNECTOR.

Has water entered the connector?

Completely remove any water inside.

Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD BANK 1">Go to Step 6.

6.CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR.

1) Turn the ignition switch to OFF.

2) Disconnect the connector from ECM.

3) Disconnect the connector from rear oxygen sensor.

4) Measure the resistance of harness between ECM connector and rear oxygen sensor connector.

Connector & terminal

(B136) No. 21 — (E25) No. 3:

(B135) No. 30 — (E25) No. 4:

Is the resistance less than 1 ??

Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD BANK 1">Go to Step 7.

Repair the harness and connector.

NOTE:

Repair the following locations.

• Open circuit in harness between ECM connector and rear oxygen sensor connector

• Poor contact of coupling connector

7.CHECK REAR OXYGEN SENSOR SHIELD.

1) Turn the ignition switch to OFF.

2) Expose the rear oxygen sensor connector body side harness sensor shield.

3) Measure the resistance between sensor shield and chassis ground.

Is the resistance less than 1 ??

Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD BANK 1">Go to Step 8.

Repair the open circuit of rear oxygen sensor harness.

8.CHECK ENGINE OIL AMOUNT AND EXHAUST GAS.

1) Check the engine oil amount. Engine Oil > INSPECTION">

2) Check exhaust gas during idling.

Does the engine oil amount drop or white smoke emit from the muffler?

Check the engine, and repair the defective part. Engine Trouble in General > INSPECTION">

After repairing the engine, replace the catalytic converter. Front Catalytic Converter"> Rear Catalytic Converter">

After the catalytic converter is replaced, perform step 2 to check the normal waveform is displayed, and then exit the procedure.

Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD BANK 1">Go to Step 9.

9.CHECK IGNITION SYSTEM.

1) Check the spark plug. Spark Plug > INSPECTION">

2) Check the status of the ignition coil connector and the spark plug terminal.

Is there any fault in the ignition system?

After repairing the ignition system, replace the catalytic converter. Front Catalytic Converter"> Rear Catalytic Converter">

After the catalytic converter is replaced, perform step 2 to check the normal waveform is displayed, and then exit the procedure.

Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD BANK 1">Go to Step 10.

10.CHECK FUEL SYSTEM.

1) Refer to and check the items in “Insufficient fuel supply to fuel injector” (except for “a. Fuel pump does not operate.”) and “Leakage or blow out of fuel”. Fuel System Trouble in General > INSPECTION">

2) Check throttle body. Throttle Body > INSPECTION">

3) Check intake manifold. Intake Manifold > INSPECTION">

Is there any fault in the fuel system?

After repairing the fuel system, replace the catalytic converter. Front Catalytic Converter"> Rear Catalytic Converter">

After the catalytic converter is replaced, perform step 2 to check the normal waveform is displayed, and then exit the procedure.

Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD BANK 1">Go to Step 11.

11.CHECK DTC.

Is any other DTC displayed?

Check the appropriate DTC using the “List of Diagnostic Trouble Code (DTC)”. List of Diagnostic Trouble Code (DTC)">

After checking the DTC, replace the catalytic converter. Front Catalytic Converter"> Rear Catalytic Converter">

After the catalytic converter is replaced, perform step 2 to check the normal waveform is displayed, and then exit the procedure.

Replace the rear oxygen sensor. Rear Oxygen Sensor">

1. OUTLINE OF DIAGNOSIS

Detect the deterioration of the catalyst function.

Detect the degradation of catalyst function using catalyst conversion efficiency.

Catalyst diagnosis is performed by comparing the catalyst monitor value and the compensation coefficient of rear oxygen sensor response.

2. EXECUTION CONDITION

Secondary parameters	Execution condition
Battery voltage	≥ 10.9 V
Barometric pressure	≥ 75.1 kPa (563 mmHg, 22.2 inHg)
Amount of intake air	< 6.2 g/s (0.22 oz/s)
Accelerator pedal position	While idling
Rear oxygen sensor output voltage after fuel cut	< 0.15 V
Estimated catalyst temperature	≥ 525 °C (977 °F) (CVT model) ≥ 525 °C (977 °F) (MT model)
Estimated rear oxygen element temperature	≥ 500 °C (932 °F)
(Integrated intake air amount during fuel cut Fuel shut-off function from above)	≥ 13.45 g (0.47 oz) Not in operation

3. DIAGNOSTIC METHOD

Judge as NG when the duration is within the predetermined time at the time when the conditions below are established by calculating the difference between the catalyst monitor value and the compensation coefficient of rear oxygen sensor response after the execution conditions are established.

(A)	Fuel cut	(D)	0.2 V	(G)	ON
(B)	Catalyst monitor condition	(E)	0 V	(H)	Disable
(C)	Rear oxygen sensor voltage	(F)	OFF	(I)	Enable

Judgment value

Malfunction Criteria	Threshold Value
Catalyst monitoring value − Rear oxygen sensor response compensation coefficient	< 0.35 g

* After 5 to 15 seconds of fuel cut recovery, the catalyst monitoring value will be calculated until the rear oxygen sensor exceeds 0.2 V.

TF = Temperature Factor

Map

Estimated catalyst temperature °C (°F)	500 (842)	500 (932)	600 (1,112)	650 (1,202)	800 (1,472)	900 (1,652)
Temperature Factor	1.25	1	1	1.25	1.25	1.25

Estimated catalyst temperature

°C (°F)

500

(842)

500

(932)

600

(1,112)

650

(1,202)

800

(1,472)

900

(1,652)

Temperature Factor

1.25

Time needed for diagnosis: Less than 1 second

Malfunction indicator light illumination: Illuminates when malfunction occurs in 2 continuous driving cycles.

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