DTC Detection Logic

WARNING: This page is about a different car, the 2019 Nissan NV3500 HD, 2019 Nissan NV2500 HD, and 2019 Nissan NV1500. However, it is still accessible from the selected car via links, so may be relevant.

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

Courtesy of NISSAN NORTH AMERICA, INC.

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

DTC No.

Trouble diagnosis name

(Trouble diagnosis content)

DTC detecting condition

Possible cause

P0420

TW CATALYST SYS-B1

[Catalyst system efficiency below threshold (bank 1)]

Three way catalyst (manifold) does not operate properly.
Three way catalyst (manifold) does not have enough oxygen storage capacity.

Three way catalyst (manifold)
Exhaust tube
Intake air leaks
Fuel injector
Fuel injector leaks
Spark plug
Improper ignition timing