Lamda/O2 sensors

[IdriveAtoB]

Hey Troops

Have an O2 sensor failure/warning (Engine Management Lamp Lit) which has happened a few times but RAC found a dodgie wire leading to the 'HT setup' but TBH I'm not 100% as just took it to a garage and they fitted a new connector and all was great for a month but the EML is lit again (both O2 sensors failure).

My question is .. are the two O2 sensors active or passive? I'm told one is in the engine and one in the exhaust manifold.

The car runs but is sluggish especially below 2000 rpm but it's also sluggish changing up/down and accelarating unless I change with higher RPM playing the gas/clutch.

I had a full service done but didn't make much difference. I did notice a change after the dodgie connector was chagned but might have been placebo effect ...

Ideally if the O2 is an active component I'd have it swapped (Engine side first I guess as maybe manages the gas/air mix) in the hope the engine runs smoother but at £120 each I'd be grateful for the petrol head input on your forum.

Many Thanks

 

Edit: the engine sounds like a diesel taxi :( 79K on the clock purchased it had 71k

 

[iantt]

when you say both o2 sensors have failed, what codes indicate this?

[IdriveAtoB]

I'm sorry the garage told me the result I have no idea the codes.

I've used this garage a while and that's 3 times they have checked the car out and it was only 1 sensor then both then RAC solved an issue with damaged wiring then the EML lit again and they checked and said both O2 sensors. They said don't worry about it but the engine is sluggish and kargaroo-ay so ideally would like fixed.

Thnaks

[MrRedman]

The other halfs 05 1.6 focus had a similar issue the garage replaced the sensor on the exhaust going by a code it turned out to be the cat 

[iantt]

the downstream sensor is only a monitor sensor that doesnt affect the running of car, upstream sensor is the one that affects fueling,

[iantt]

the downsteam sensor monitors the catalyst efficiency, both sensors very rarely fail together.