DTC: P0420

Search Bulletins/Recalls for P0420

Trouble diagnosis name: Catalyst system efficiency below threshold Bank 1

Diagnosis Logic

The ECM monitors the switching frequency ratio of heated oxygen sensors 1 and 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 heated oxygen sensors 1 and 2 approaches a specified limit value, the three way catalyst (Manifold) malfunction is diagnosed.

DTC detecting condition:

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

Possible cause:

• Three way catalyst (Manifold)
• Exhaust tube
• Intake air leaks
• Fuel injectors may be faulty
• Fuel injector leaks
• Spark plugs may be faulty
• Improper ignition timing
• Engine Control Module (ECM) program