P0420 TOYOTA - Catalyst System Efficiency Below Threshold Bank 1

P0420 TOYOTA - Catalyst System Efficiency Below Threshold Bank 1

The catalytic converter is a part of the exhaust system that looks kind of like a muffler, although it's job is very different from that of a muffler. A catalytic converter's job is to reduce emissions from the exhaust. The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. Oxygen sensors are also referred to as O2 sensors. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). Catalytic converters are not normally a "wear" type item, that is they are not designed to wear out and need replacement. If they have failed, it is likely due to something else that caused it to fail. This is what a P0420 means in simplified terms.

P0420 Toyota Causes :

  • A code P0420 may mean that one or more of the following has happened:
  • Leaded fuel was used where unleaded was called for (unlikely)
  • A damaged or failed oxygen / O2 sensor
  • Downstream oxygen sensor (HO2S) wiring damaged or connected improperly The engine coolant temperature sensor is not working properly
  • Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe
  • Failed or underperforming catalytic converter (likely)
  • Retarded spark timing
  • The oxygen sensors in front and behind the converter are reporting too similar of readings
  • Leaking fuel injector or high fuel pressure
  • Cylinder misfire
  • 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 symptoms 


Engine Light ON (or Service Engine Soon Warning Light) 
 

P0420 Toyota 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.