P0420 NISSAN - Catalyst System Efficiency Below Threshold Bank 1

P0420 NISSAN - Catalyst System Efficiency Below Threshold Bank 1

P0420 Nissan Description

The Engine Control Module (ECM) monitors the switching frequency ratio of heated oxygen sensors 1 (front O2 sensor) and heated oxygen sensors 2 (rear O2 sensor). A three way catalyst converter (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 malfunction is diagnosed.

Causes Of P0420 Nissan :

A code P0420 may mean that one or more of the following has happened:

  1. Leaded fuel was used where unleaded was called for (unlikely)
  2. A damaged or failed oxygen / O2 sensor
  3. Downstream oxygen sensor (HO2S) wiring damaged or connected improperly
  4. The engine coolant temperature sensor is not working properly
  5. Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe
  6. Failed or underperforming catalytic converter (likely)
  7. Retarded spark timing
  8. The oxygen sensors in front and behind the converter are reporting too similar of readings
  9. Leaking fuel injector or high fuel pressure
  10. Cylinder misfire
  11. Oil contamination

When is the code detected?

- Three way catalytic converter Bank 1 does not operate properly.

- Three way catalyst converter Bank 1 does not have enough oxygen storage capacity.

Possible Solutions

Some suggested steps for troubleshooting and fixing a P0420 error code include:

Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.

Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).

Inspect the downstream heated oxygen sensor, replace if necessary

Replace the catalytic converter

Diagnostic Tip

Generally speaking you can look at the temperature of the exhaust just before and just after the converter using an infrared temperature gun. The output should be about 100 degrees Fahrenheit hotter when the engine is fully warmed up. Overall probably the biggest mistake vehicles owners make when they have a P0420 code is to simply replace an oxygen sensor (02 sensor). It is important to do proper diagnosis so you're not wasting money replacing parts unnecessarily.

We strongly recommend that if you need to replace the catalytic converter that you replace it with an original manufacturer brand unit (i.e. get it from a dealership). Second choice would be a high-quality replacement part such as a 50-state legal cat. There are many stories in our forums where folks replaced the cat with a cheaper aftermarket one only to have the code return shortly thereafter.