P0420 NISSAN -

Question

2006 Nissan Pathfinder was running erratically. Found out Nissan had a recall on ECM relay inside the IPDM module. Also found out a temporarily fix. Swap the Fog relay with ECM relay. I did and drove with no problems to Nissan. Made Nissan aware of the swap I had performed. Nissan installed a new EDM relay and put the Fog relay back in its original position.

Few miles after driving from Nissan, “Service Engine Soon” light came on. I hooked car to engine analyzer and got the “P0420 catalyst efficency low (B1) bank 1 rear O2 sensor”.

Before I do anything I want to see if anyone else has had the same problem. Not sure if

1. New ECM relay is bad.
2. Maybe entire IPDM module should have been changed
3. Bad O2 sensors
4. Leaded fuel was used where unleaded was called for
5. A damaged or failed oxygen sensor (HO2S)
6. Downstream oxygen sensor (HO2S) wiring damaged or connected improperly
7. The engine coolant temperature sensor is not working properly
8. Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe
9. Retarded spark timing
10. The oxygen sensors in front and behind the converter are reporting too similar of readings
11. Leaking fuel injector or high fuel pressure
12. Cylinder misfire
13. Oil contamination

Thank you,

SV

Answer 1

From what I have seen at my shop, #4 and #11 are usually the most common causes of this problem. In fact sometimes just by using high octane gas will take care of the problem.