OBD code P0420 2005 Citroen Picasso?

In this case the customer is getting Check engine light on dash.Its steady engine light.
After getting the engine computer scanned.The error code P0420 is retrieved.
The client replaced the front Lamna sensor switch.But the error is still reoccurring.


Fault code P0420 ..this is a code relating to sensor Below Threshold (Bank 1)

Probable and usual causes for this are : Catalytic converter, wiring, Heated Oxygen Sensor (HO2S) 2

Bank 1 you can ignore - as this relates to V engines where you have bank one and bank two. The machine just comes up with that . You will note that under the probable cause above - apart from the cat... and the wiring .. it mentions the o2 sensor - but as opposed to the front - pre car o2 sensor that you say you have had changed, the uninterpretation of the fault code relates to the post / after cat sensor - ie, sensor 2.

So it looks like maybe you have replaced the wrong sensor and the fault lies with the post cat sensor all the time..

In some cases the problem may not be the actual sensor at fault - wiring / connection faults are common - so that should be carefully checked first - and the sensor replaced only if all else checks out.

The EML - engine light will be on because the fault / code is there - Once the other relevant sensor ( or its wiring etc as above is sorted ) that light should go off. If it doesn't, the code will need to be cleared using the diagnostic equipment / ecu reset - and the light will stay out then.


This details will help.
Thanks.

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