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 1 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 1 malfunction is diagnosed.

Courtesy of NISSAN NORTH AMERICA, INC.

DTC No.

CONSULT screen terms

(Trouble diagnosis content)

DTC detecting condition

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.