Re:Emissions warning light

Same with my diesel SAAB - filled with fuel at Asda and it ran like a bag of broken spanners. put Shell V-Power in and it ran like silk - like it had just been tuned.

Some interesting stuff here. The day before my light came on I was doing around 50 and had a sudden lack of power, lasted around 10 seconds then all was well. I have only had my Jimny a month but it had been stood a while and I am now thinking there may be some dodgy fuel in the tank. I keep filling up so hopefully it will work through. Since re-setting the emissions light it has not come back on. I read with interest Mr Headroom's comments that he also reset his and then was clear for three months without faults.

I have purchased a code reader for next time, because it’s not if, it’s when

Plenty of people use supermarket fuel without issue, and I know they don't order the dregs from the tank just to make it cheap.
I worked at an fuel distribution point and each tanker got filled from the same tank, additive packs added per customer, hence some of the extra cost. Texaco and some supermarkets used this distribution point, we maintained the control system.
Currently Tesco sell BP momentum 99 and regular unleaded, well they did when I filled up today.

I can't tell you why your EML light went off with other brands, all I know is how fuel is distributed and that my EML remains off even though I exclusively use supermarket supplied fuels in all my vehicles.
If problems exist it's more likely to be how it is stored once it has been delivered to the individual Petrol station. I have no doubt you have had problems, but it's a big claim to say issues exist with supermarket supplied fuel.

Anyhow each to their own

So I got my code reader and the dreaded light came on.

I am showing code P0031 HO2S heater control circuit Low Bank 1 Sensor 1.

Is this the sensor on the exhaust manifold?

Thanks