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Mike
Mike, Technician
Category: UK Ford
Satisfied Customers: 39198
Experience:  34 years experience of motor vehicle diagnostics
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Ford focus: engine management light..me its the catalytic converter

Customer Question

Hi, I have a ford focus 03, 1.6, 57000, and have had the engine management light on for over 2 months now with DTC code P0420. I realise I am using much more fuel on my trips and a mechanic has told me its the catalytic converter. He claimed to have fixed it temporarily which only lasted a few days. Another mechanic has advised that i try fuel injector cleanser when I next have an empty tank. I am unsure if this is a permanent fiX the problem. I have read a number of posts on here which confirms the problem is caused by engine misfire which inturn burns the sensors etc.. My question is what causes the engine to misfire in the first place? Secondly, If i replace the coil and the catalytic converter would that solve the problem or do I need to find the root of why the engine misfires? Grateful if you could help please. I am desperate for a solution as it is costing me a great deal in fuel. Please help.. Thanks v much . Steve
Submitted: 5 years ago.
Category: UK Ford
Expert:  Mike replied 5 years ago.

MIKE :

Hello and Welcome to justanswer...

Customer:

thanks MIKE..

MIKE :

Hi there...You are right to ask those questions - because thats the root of your problems...

MIKE :

Has anyone said what that code is for exactly ?

Customer:

yES,

Customer:

the mechanic claims it is for the catalytic converter

Customer:

have you seen my questions?

MIKE :

Ok - let me just have a look because I cant remember the meaning of every code ;) What is the cars Full reg number?

MIKE :

yes I have yes..

Customer:

reg no is

Customer:

ry03wxs

MIKE :

great... give me a min to bring up your car..

Customer:

ok

MIKE :

ok - is this your car ...?

MIKE :














Focus 1998-2005, 1.6L Zetec-S/Duratec EFI (100PS), Moondust Silver (Metallic)
VIN Number: WF0AXXGCDA3Y52626
















Registration Number: RY03WXS
Registration Date: 06.07.2003
Registration Country: GB
Customer:

yes it is...

MIKE :

good - another min to look up the code..

Customer:

ok.....

MIKE :

ok..

MIKE :

this is the code you have - and its meaning....

MIKE :







P0420Catalytic converter system, bank 1 - efficiency below thresholdCatalytic converter, wiring, HO2S 2
MIKE :

Now - is the car misfiring / juddering?

Customer:

yes....i know....

Customer:

juddering a bit....

MIKE :

yes but you said the mech said the cat was at fault - there is more to it than that - and a failed cat wont cause a misfire

Customer:

what is a misfire?

MIKE :

ok - when you say the mech "fixed it for a few days".. what do you mean / what happened?

Customer:

I mean the light went off for a few days and came back on..

MIKE :

sorry for all the questions - I have to be sure of whats happening etc

Customer:

he said not to accelerate at first start of the engine in the mornings but to leave the car staionery for a few mins..

Customer:

so that the engine runs for a while..

MIKE :

right - so all he did was clear the fault codes which switches the light off - thats not a fix Im afraid -

MIKE :

what sort of garage is this ? ( honest question )

Customer:

The juddering seems to happen when the car is stationary, I feel the engine hums a bit high..

Customer:

sometimes when you apply the clutch, it feels the car is about to stall

Customer:

but it doesnt....

Customer:

so, what i am saying is i feel the engine is not running as smooth...

Customer:

I wonder what the misfire is...

MIKE :

Ok... misfire... a misfire -is when the engine is not running on all 4 cyinders - ie, 3 or 4... meaning that the engine runs badly - rough, no power , all the time...


Customer:

if i changed the coil and bought a new entire exhaust will that solve it?

MIKE :

I dont think from what you say, that it is actually missing - if it were you would have a misfire fault code

Customer:

oh ok... then i wouldnt say so... it runs fine and has power../!

MIKE :

ok.. so , it has power - but the EML (ight is on ) yes? Is it full / normal power?

Customer:

yes, the EML light is on..

Customer:

the engine has full opower..

Customer:

but consumes fuel

MIKE :

ok good - now we are moving - ruling things out fast..

Customer:

a lot more these days..

MIKE :

yes - this is your way forward now..

MIKE :

remember the o2 sensor comment re the fault code?

Customer:

P0420?

MIKE :

This can be causing all your probems - but first..the connector / wire to the o2 sensor needs careful checking - they are known to burn the wire on the engine / exhaust... or get a bad connection on its plug.

MIKE :

This will - cause what youhave...so that must all be checked first !

Customer:

OK, ill check that....

MIKE :

If any problems are found - rectify and retry it. The light should go off and stay off.

Customer:

ok, so if it doesnt work would a new coil and converter to the trick?

MIKE :

If no probems are found - then, the next move is to have the car tested on an mot exhaust gas machine - not a plug in diagnostic machine.

MIKE :

no - forget the coil

Customer:

ok, I see... I will try that Mike...

MIKE :

The mot test machine will see if the o2 sensor is working or not

Customer:

I will go to kwik fit for that

Customer:

Thanks for the advise Mike..

Customer:

I will come back after xmas with the results..

MIKE :

if the o2 sensor is out of scale ( it should be within the readings off 0.97 - 1.03 ).. if its outside that - fit a new sensor.

Customer:

how do I let you know the outcome?

MIKE :

hang on a mo...

MIKE :

if fitting the sensor then cures it - then thats that. IF not - , then you need a new cat.

Customer:

oh I see...

MIKE :

further -

MIKE :

most cat suppliers will not warrant the new cat - if you dont fit a new o2 sensor..so dont fit a cat and not a new sensor. (that way round)

MIKE :

further...

MIKE :

So if you work through it as above - you wil have this sorted ;)

Customer:

ok, so a new sensor before the cat right?

MIKE :

correct - yes... and be sure to fit a "non universal " type - make sure you get a Bosch or similar.

Customer:

Thank you soo very much...

MIKE :

Universal ones are cheap - rubbish and dont last .

Customer:

your help is much appreciated...

MIKE :

No problem at all...

Customer:

how do i let u know its solved...

MIKE :

Ok - .. if we are done now...

Please click the Accept button for me - Thank You ...and if you do need / wish to get back to me after - you can do so just by coming back to this post and use the Reply button - your reply will then come straight back to me .. and Im always happy to help further....
Please note , you need to press the Accept button even if you are a subscriber to justanswer - thank you again.


MIKE :

that can be for more help - or just to let me know you are smiling !

Customer:

thanx....mike...

Customer:

all the best...

MIKE :

No problem at all. Very pleased to have helped.

MIKE :

and all the best to you too ;) Thank you for using myself and justanswer .

MIKE :

(please dont forget the accept - as thats how I get credited for helping you ... Thank you again.

Expert:  Mike replied 5 years ago.
Hello again..

Im sorry the chat system appeared to seize - but we were just finishing up..

All the info / our discussion is showing above - you can print it out if you like...

Im very pleased to have helped you -

Please remember click the Accept button for me - Thank You ... and if you do need / wish to get back to me after - you can do so just by coming back to this post and use the Reply button - your reply will then come straight back to me .. and Im always happy to help further....
Please note , you need to press the Accept button even if you are a subscriber to justanswer - thank you again.

Kind Rgds - MIKE.