Hi guys,

 

I wonder if you're able to help me identify this blue wire under the engine bay? It's a Mk1 Focus 1.8 petrol, almost underneath the battery.

Don't know if it's related, but I recently had an O2 sensor warning, followed by battery warning light, also followed by coolant leak 🤣. While checking under the bonnet, I saw this dodgy looking wiring. Was wondering if the coolant from the cracked thermo housing was getting on it. 

Anyway, in the end the mechanic replaced the thermo housing, and it turned out he didn't even look at the wiring or the battery despite me telling him what I just told you. But I realised that my battery is 6 years old now, so I decided it was probably just on its way out hence the O2 sensor low voltage warning, and for the sake of £50 I just replaced it. 

However....this gnarly looking wire is still bothering me. It looks like it's not only exposed but one of the wires is severed and sticking out. 

Any ideas? 

 

 

Wait....don't tell me....it's the O2 sensor, isn't it? 😂🤣

Looks like you found it

New sensor will come with the wiring back to the blue plug

Excellent, thank you. I had watched a few YouTube videos about replacing the O2 sensor, but it was in a different place, which is what confused me. 

Obviously either a different model, or a different sensor (I know there are two).

11 hours ago, DrPepper said:

Excellent, thank you. I had watched a few YouTube videos about replacing the O2 sensor, but it was in a different place, which is what confused me. 

Obviously either a different model, or a different sensor (I know there are two).

You answered your own question again . There's 2 . upstream and downstream of the catalytic converter. 

Downstream is the one that's broke. 

Part number is 1035595 . 

https://www.ebay.co.uk/itm/265575169268?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=o28gWE1XQSu&sssrc=2349624&ssuid=&var=&widget_ver=artemis&media=COPY

Excellent stuff, thanks Ian. That's original Ford, plus it's cheaper that EuroCarParts!

 

The thing that confuses me about this is....the fault code I got was P0136 "O2 sensor circuit malfunction, bank 1, sensor 2".

From what I've read, that's the post-cat sensor. But ...isn't the one pictured above the pre-cat sensor 1?

Ok I've answered my own question again! Bit hopefully it'll be useful in future for anyone else with the same issue. 

Turns out you can see the cat right there in the photo 😂 I was expecting it to be horizontal and further towards the rear. Annoyingly the Haynes manual doesn't have a photo of it!

And also, from research, found that green is pre cat, blue is post cat.

It's taken me literally days to find that out. Don't understand why Ford went to the trouble to colour code them, but apparently what the colours mean is a secret!

Nowadays the cat is generally fitted directly to the exhaust manifold. This helps it warm up quicker (they don't work until they get hot) and also has the benefit it makes it harder for the scum to steal them.