Fiesta 2007 HO2S fault

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2007 petrol 1.4 fiesta, showing P0030 heater control circuit bank 1 sensor 1. After clearing, Logs the fault again immediately you turn the engine on (not with just the ignition on). Same whether engine is hot or cold.
Assuming this is the pre-cat one at the top rear of the engine bay, I’ve unplugged it and get 12V across 2 of the 4 terminals on the supply, when the ignition’s on, and for about 10secs after turning ignition off.
I’m guessing I should replace the lambda sensor, just wondered if there’s anything else I can check/test either with my OBD reader (a very basic one) or on the terminals to be more sure where the fault lies?
If I get a new one I’ll get a half decent one (£80 upwards) rather than a cheapo.

Any advice much appreciated...
 
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I would think that your 12v measurement is actually the sensor heater, the switching signalling of the probe is only up to around 1v if I recall.
before diving in, try with the sensor unscrewed, just in case the cat is starting to block - but I would guess that a new sensor is needed.
The German firm Hella has some excellent tips on their website, under lambda sensor testing and trouble shooting.
Is the performance of the car affected?
John :)
 
Thanks John
Yeah I think the 12v is the heater supply rather than anything to do with the sensor signal, and the fault appears to relate to the heater circuit too.

Not sure if the performance is affected as I’ve only recently got the car. It feels ok for an old motor to be fair, nice and pokey 1.4 (reminds me of my youth when fiesta 1.4S was a thing)

I’ll attempt to remove it, although not sure whether I’ll manage to - the existing one is surrounded by a heat shield which I’ve no idea is removable or not, I guess I need to get a lambda sensor spanner tool first.
Pic attached, reckon that’s accessible with the right tool, without removing more bits?
Thanks
 

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With those, I have two options.....I have the split lambda socket, that allows the wires to remain but if that fails its a deep drive socket, cutting the wires off first :eek: Sometimes these things can be ferociously tight, other times they give up without too much struggle.
I guess it just depends on the luck of the day! At least the sensor is well supported, not flapping round on an exhaust pipe.
Be lucky!
John :)
 
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Cheers John, am I right in thinking that heat shield isn’t supposed to be removed in order to do this? Thanks
 
The theory is the heat shield should be able to stay put - if your socket is slim enough!
Typically, those 10mm bolts have their heads rusted away :(
John :)
 
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