I recently had a engine management light come on, and had a Jag specialist check it - it was the CAT. He removed the error message, and said it might be because I had used supermarket fuel. He advised to use only the main fuel suppliers (Shell, BP, Esso etc), and even then to use the high octane fuel. I thought this old chestnut of supermarket fuel had been resolved years ago - that is was no different, but maybe I'm wrong. Has anyone else got any experience of this?

 

Your mechanic is living in the past. I buy fuel for my car at my local Kroger and have never had a problem. I would be more concerned about filling up at a station that has very low usage.

 

Don't go back to that "specialist". Maybe he's OK on a 1970s car.

If the MIL comes back on, read the codes. Get an OBD tool now so you're ready.

 

+1 on above comments. I'd find a different specialist to go to, the present guy sounds like he's lost in the past and poorly educated to start with.

The supermarkets and 'mom and pop' stations all get their fuel from the same refineries as the brand names. There might be some difference in additives (maybe) but it takes thousands of miles for any difference to show up.

The octane rating of a fuel is not an indication of quality or quantity of additives. I believe your car was designed for 95 RON octane. Anything higher is a waste of money.

 

A bad load of fuel can cause problems, but you cannot fault the quality of supermarket fuel in general. Switch fuels for a few tanks and see if the error returns. More likely it might be one of the oxygen sensors and how much mileage is on it.

 

I just noticed that we all failed to ask for the actual code, not someone's interpretation. If the CEL comes on again get the code read and tell us what it is. Also, where are you? There is a Farnborough in several US states, Can. and the UK, I believe.

 

Thank you all for your replies. Greatly appreciated. I didn't get the actual code - he erased it before I saw it. Sorry - silly of me not to ask. He just said it was the left hand bank CAT getting weak. By the way it is a 2001 XKR with 88,000 miles - although regularly serviced, I don't know if the oxygen sensor has ever been replaced - its a weekend boys toy, so doesn't do a lot of miles, less than 800 between MOT's. Could that be the problem - not using it enough? My man said by clearing the code, it could go on fine for ages, or could come back again quickly. I have now purchased a MAXISCAN MS309. Only cheap, but it seems to do the job, well so far without any error codes to read at the mo!! If you think that won't do the real job, please feel free to let me know. My Farnborough is one of 3 in the UK (popular name!!!) but is the one in Hampshire, UK, famous (or infamous??) for the Farnborough Air Show every other year. Thank you all again. Tony

 

I have seen pictures from the airshow, very impressive. I suspect the code was actually for a failing O2 sensor. Your scanner should be able to read it.