03 1.6 Engine warning light - Cornfields
Re. my Ford Focus LX 2003. My problem is that the car engine warning light stays on permanently but does not appear to affect the running of the car. My garage has done numerous diagnostic tests and replaced both Lambda sensors and reset engine management lamp but it still stays on. I would appreciate any assistance. Many thanks.

Edited by Pugugly {P} on 14/02/2008 at 22:05

Engine warning light - adverse camber
try posting in technical and let people know WHAT ENGINE ????
Engine warning light - Pugugly {P}
Moved over from Discussion.........
03 1.6 Engine warning light - Screwloose

What codes are they finding?
03 1.6 Engine warning light - Cornfields
I don't have that information to hand but will speak to the Garage tomorrow and come back with more details. Again many thanks for your prompt reply.
03 1.6 Engine warning light - Cornfields
Hello Screwloose,

Herewith Code No. P0420

Look forward to any advice you can give

Regards Cornfields
03 1.6 Engine warning light - Screwloose

P0420: Catalytic converter system bank 1 - efficiency below threshold.

Seems a common and easy enough code?

With the cat hot, if the post-cat oxygen sensor signal is fluctuating in synch with the upstream one then the cat is gone and that code appears.

Do they clear it and then it returns a few days later?
Have they sampled the exhaust gases to confirm cat failure?
Have they measured the in and out cat temperatures?
Have they even put a scope on both sensors and watched their output voltages together?

Are you in the SE and affected by last Feb's contaminated fuel incident?
03 1.6 Engine warning light - Cornfields
Hi screwloose, the engine warning light did clear today when the Garage
was requested for the code but know doubt it will return like it has before. Will speak to the garage for answers to your remaining questions and get back to you. In respect of contaminated fuel we do live in the S.E. (Herts.)but always purchase our petrol from Sainsburys and have not heard that there has been a problem with this supplier (fingers crossed). Again many thanks,
03 1.6 Engine warning light - Cornfields
Hi Screwloose, have had a catalytic converter fitted just this last week and since then the engine warning light has not appeared. Many thanks again for your sound advice.
Regards, Cornfields

Edited by Pugugly on 07/03/2008 at 18:40

03 1.6 Engine warning light - Screwloose

Glad that they - finally - got there.
03 1.6 Engine warning light - eeo
I too have been having a similar problem and thought I'd ask your advice if you'd be so kind as you seem knowledgeable on the subject. It's quite a story so apologies in advance.

I had a custom made sports CAT fitted last October as the old one dropped to bits pretty much. A week after fitting, the engine management light came on. It returned to the garage for resetting perhaps 5 or 6 times up until March. The guys there couldn't understand why. They wanted me to have it "chipped" or tuned or whatever but that was obviously not the solution I wanted as it would have cost me about £150 and I was reluctant to pay for it.

In April the car then had it's MOT, which it failed due to the emissions levels. It went back to the garage and had a "standard" CAT fit. It passed the MOT, just! Since the MOT, the light has come on occassionally. I have had to do the battery unplugging trick to clear it and then it generally stays off for a week or two.

In September I fit a new pre CAT lambda sensor. Again the light returned. Just last week I had the car at a garage, the mechanic again got the same P0420 code on his testing equipment and loosely advised that it was probably the CAT or the sensors.

I am at a total loss to be honest with you, both mentally and financially. Any assistance you or anyone you know could provide would be gladly received.

03 1.6 Engine warning light - Screwloose

Let's start with full car details and year.

Clearly; this "custom-made" cat was rubbish. It's the post-cat sensor that monitors cat efficiency, so you changed the wrong one [not that there would have been anything wrong with the either one.]

Is the cat now fitted a genuine manufacturer's one?

Value my car