Hi everyone. Recently I had the dreaded "oxygen sensor 1 bank 1 voltage low" fault come back on my street Ka. I have replaced the sensor in the past but now the issue proceeds, any ideas what to look for?

If it was a cheap sensor, they rarely last long.  Though it's always worth checking the wiring isn't in poor condition anywhere between the PCM & the sensor.

Yeah checked all the wiring, seems to be pretty good condition with no breakages or signs of rust. The plug is good too

I'd probably try a better quality sensor if the first one was unbranded.

There is a possibility that the sensor is reading correctly and there is genuinely too much oxygen in the exhaust.  That could be caused by either a vac leak around the inlet, or a hole in the exhaust before the sensor.

The engine sounds normal so I wouldn't say there's a exhaust leak, but it is possible there is a vacuum leak. I think I will probably replace the sensor first with a genuine one and see what happens after

I have noticed though, the engine is consuming an extremely large amount of fuel now

Just now, Fords0n said:

I have noticed though, the engine is consuming an extremely large amount of fuel now

Well, that should be high voltage on the lambda if it's running rich. 

Though it may be using a default map if the lambda readings are too unreliable to use.

Yeah, i have no idea what this car is doing now lol, btw it just started another fault saying P0171 system too lean bank 1 and I'm noticing a tiny miss fire happening. Possible it has a small intake leak? When it idles it's fluctuations are between 870 and 900 revs which seems pretty normal

Update: bit later we discovered the sensor is working as intended, and there are no leaks anywhere. Spoke to ford mechanics, they said update the software for the aftermarket sensor, £150 should fix it. Maybe a stupid question but would a remap fix it instead? Just thinking as I was gonna remap it anyway 

Hmm.  That is the case with later models (particularly 1.0 EcoBoost).  But I haven't heard of the older models needing a PCM update with a new lambda.

A remap won't fix this issue as that's stored in a different part of the PCM.

Not sure there's any real world gains to be had from a remap on these to make it financially viable?

Talked to some other owners of the street Ka, they said they experienced small performance changes but what I'm after is MPG because currently despite only being a 1.6 it's guzzling fuel and I was told the best way to fix that is remap it. Of course the oxygen sensor will be part of the issue though because it's not running efficiently.

Tbh I've spent so long working on the car, no leaks no sensor issues and checked everything I can think of and It seems fine. I think software is the last thing I haven't looked at but I honestly don't know, could be the issue or might not be

Another update: in my own madness I decided to take the whole intake system apart in my empty time, after cleaning loads of carbon from the intake manifold and cleaning the throttle body I couldn't find any issues, so I re assembled the engine and tried it again. No fault codes and no miss fire, I have no idea what I did but I fixed something lol, the sensors looked completely clean to me