Nissan Altima 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


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.


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

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