Nissan Altima (L32) 2007-2012 Service Manual: P0420 three way catalyst function

DTC Logic

DTC DETECTION LOGIC

The ECM monitors the switching frequency ratio of air fuel ratio (A/F) sensor 1 and heated oxygen sensor 2.

A three way catalyst (manifold) with high oxygen storage capacity will indicate a low switching frequency of heated oxygen sensor 2.

As oxygen storage capacity decreases, the heated oxygen sensor 2 switching frequency will increase.

When the frequency ratio of A/F sensor 1 and heated oxygen sensor 2 approaches a specified limit value, the three way catalyst (manifold) malfunction is diagnosed.

DTC CONFIRMATION PROCEDURE

1.PRECONDITIONING

If DTC Confirmation Procedure has been previously conducted, always turn ignition switch OFF and wait at least 10 seconds before conducting the next test.

TESTING CONDITION: Do not hold engine speed for more than the specified minutes below.

>> GO TO 2.

2.PERFORM DTC CONFIRMATION PROCEDURE-I

CAUTION: Always drive vehicle in safe manner according to traffic conditions and obey all traffic laws.

1. Start engine and warm it up to the normal operating temperature.

2. Repeat the following procedure 3 times.

- Drive vehicle at a speed of 80 km/h (50 MPH) or more for at least 3 consecutive minutes.

NOTE: Keep the vehicle speed as steady as possible during the cruising.

- Stop vehicle with engine running.

NOTE: Never turn ignition switch OFF.

3. Select “DTC & SRT CONFIRMATION” then “SRT WORK SUPPORT” mode with CONSULT-III.

4. Drive vehicle at a speed of 80 km/h (50MPH) or more until “INCMP” of “CATALYST”changes to“CMPLT”.

NOTE: • Keep the vehicle speed as steady as possible during the cruising.

• It will take at most 3 minutes until “INCMP” of “CATALYST” changes to “CMPLT”.

5. Check 1st trip DTC.

1. Start engine and warm it up to the normal operating temperature.

2. Repeat the following procedure 3 times.

- Drive vehicle at a speed of 80 km/h (50 MPH) or more for at least 3 consecutive minutes.

NOTE: Keep the vehicle speed as steady as possible during the cruising.

- Stop vehicle with engine running.

NOTE: Never turn ignition switch OFF.

3. Check 1st trip DTC.

Is the inspection result normal? YES >> Go to EC-287, "Diagnosis Procedure".

NO >> INSPECTION END

Diagnosis Procedure

1.CHECK EXHAUST SYSTEM

Visually check exhaust tubes and muffler for dent.

Is the inspection result normal? YES >> GO TO 2.

NO >> Repair or replace.

2.CHECK EXHAUST GAS LEAK

1. Start engine and run it at idle.

2. Listen for an exhaust gas leak before the three way catalyst (manifold).

Is exhaust gas leak detected? YES >> Repair or replace.

NO >> GO TO 3.

3.CHECK INTAKE AIR LEAK

Listen for an intake air leak after the mass air flow sensor.

Is intake air leak detected? YES >> Repair or replace.

NO >> GO TO 4.

4.CHECK IGNITION TIMING

For procedure, refer to EC-28, "IGNITION TIMING : Special Repair Requirement".

For specification, refer to EC-555, "Idle Speed" and EC-555, "Ignition Timing".

Is the inspection result normal? YES >> GO TO 5.

NO >> Follow the EC-24, "BASIC INSPECTION : Special Repair Requirement".

5.CHECK FUEL INJECTOR

1. Stop engine and then turn ignition switch ON.

2. Check the voltage between ECM harness connector and ground.

Is the inspection result normal? YES >> GO TO 6.

NO >> Perform EC-463, "Diagnosis Procedure".

6.CHECK FUNCTION OF IGNITION COIL-I

CAUTION: Do the following procedure in the place where ventilation is good without the combustible.

1. Turn ignition switch OFF.

2. Remove fuel pump fuse in IPDM E/R to release fuel pressure.

NOTE: Do not use CONSULT-III to release fuel pressure, or fuel pressure applies again during the following procedure.

3. Start engine.

4. After engine stalls, crank it two or three times to release all fuel pressure.

5. Turn ignition switch OFF.

6. Remove all ignition coil harness connectors to avoid the electrical discharge from the ignition coils.

7. Remove ignition coil and spark plug of the cylinder to be checked.

8. Crank engine for 5 seconds or more to remove combustion gas in the cylinder.

9. Connect spark plug and harness connector to ignition coil.

10. Fix ignition coil using a rope etc. with gap of 13 - 17 mm (0.52 - 0.66 in) between the edge of the spark plug and grounded metal portion as shown in the figure.

11. Crank engine for about 3 seconds, and check whether spark is generated between the spark plug and the grounded metal portion.

Spark should be generated.

CAUTION: • Do not approach to the spark plug and the ignition coil within 50 cm (19.7 in). Be careful not to get an electrical shock while checking, because the electrical discharge voltage becomes 20kV or more.

NOTE: When the gap is less than 13 mm (0.52 in), the spark might be generated even if the coil is malfunctioning.

Is the inspection result normal? YES >> GO TO 10.

NO >> GO TO 7.

7.CHECK FUNCTION OF IGNITION COIL-II

1. Turn ignition switch OFF.

2. Disconnect spark plug and connect a known-good spark plug.

3. Crank engine for about 3 seconds, and recheck whether spark is generated between the spark plug and the grounded metal portion.

Spark should be generated.

Is the inspection result normal?

YES >> GO TO 8.

NO >> Check ignition coil, power transistor and their circuits. Refer to EC-470, "Diagnosis Procedure".

8.CHECK SPARK PLUG

Check the initial spark plug for fouling, etc.

Is the inspection result normal? YES >> Replace spark plug(s) with standard type one(s). For spark plug type, refer to EM-99, "Standard and Limit".

NO >> Repair or clean spark plug. Then GO TO 9.

9.CHECK FUNCTION OF IGNITION COIL-III

1. Reconnect the initial spark plugs.

2. Crank engine for about three seconds, and recheck whether spark is generated between the spark plug and the grounded portion.

Spark should be generated.

Is the inspection result normal? YES >> INSPECTION END NO >> Replace spark plug(s) with standard type one(s). For spark plug type, refer to EM-99, "Standard and Limit".

10.CHECK FUEL INJECTOR

1. Turn ignition switch OFF.

2. Remove fuel injector assembly.

Refer to EM-36, "Removal and Installation".

Keep fuel hose and all fuel injectors connected to fuel tube.

3. Disconnect all ignition coil harness connectors.

4. Reconnect all fuel injector harness connectors disconnected.

5. Turn ignition switch ON.

Does fuel drip from fuel injector? YES >> GO TO 11.

NO >> Replace the fuel injector(s) from which fuel is dripping.

11.CHECK INTERMITTENT INCIDENT

Refer to GI-42, "Intermittent Incident".

Is the inspection result normal? YES >> Replace three way catalyst assembly.

NO >> Repair or replace harness or connector.