1.25 2012 Fiesta

Engine light is on and with a scanner i get the P0420 error code

On looking at the sensor data I get the following (as a snap shot at idle):

 

Oxygen sensor 1 Bank 1 Voltage - 0.22v

Oxygen sensor 1 Bank 1 Short term fuel trim - 4.69%

Oxygen sensor 2 Bank 1 Voltage - 0.74v

Oxygen sensor 2 Bank 1 Short term fuel trim - n/a%

 

The values vary a little, but the Oxygen sensor 2 Bank 1 Short term fuel trim value always says n/a

Does this mean the sensor is not working and needs replacing.....?

And do I assume that this is the down stream (second) sensor...?

 

 

 

 

Sensor 2 is the downstream sensor, are you checking this when the engine is cold or up to temperature, the car only uses the downstream sensor for fuel trim once the engine is up to temperature.

7 hours ago, Felix. said:

Does this mean the sensor is not working and needs replacing

If the Sensor was not working it would almost certainly throw up a Code, not a P0420 one.

12 hours ago, Neb_engineer said:

Sensor 2 is the downstream sensor, are you checking this when the engine is cold or up to temperature, the car only uses the downstream sensor for fuel trim once the engine is up to temperature.

Yes

Catalyst temperature Bank 1 Sensor 1 - 501.1 C

Catalyst temperature Bank 1 Sensor 2 - 501.1 C

 

On Forscan it states

Code: P0420 - Catalyst System Efficiency Below Threshold Bank 1 

 

Status:

DTC Maturing - Intermittent at Time of request

Malfunction Indicator Lamp is Off for this DTC

Test not complete

 

 

 

I've still got this error code popping up

I've replaced both oxygen sensors now and its still appears

I've thought about washing out the cat - do you think this will have an effect?

 

Washing out a catalytic converter is rarely successful.


The inside core of a catalytic converter consists of a ceramic honeycomb structure that is coated with precious metals like Platinum, Palladium and Rhodium. These metals are used to convert the exhaust gasses by a chemical reaction:

Rhodium --> converts nitrogen oxides into nitrogen and oxygen.

Platinum and Palladium --> converts carbon monoxide into carbon dioxide and converts hydrocarbons (unburned fuel residues) into carbon dioxide and water.


The precious metals inside a catalytic converter are subjected to chemical and thermal wear. As a result of this proces the catalytic converter becomes less effective and eventually fails its efficiency threshold.

Washing out the catalytic converter does not magically restore the chemically/thermally worn-out precious metals.


Washing out the catalytic converter only makes sense when the core is covered with soot, oil etc. that prevents the precious metals to chemically react with the exhaust gasses. When this is the case the catalytic converter is usually the least of your problem.

Is there another suggestion as to what the issue is...?

Cat faulty and needs replacing. 

You have an Ex-Cat, it is deceased, expired, or simply just buggered.

Time for a new one I think.

Darn!

Well I think I have ruled out everything else