The ‘engine light’ comes on on occasionally on our car (a 2001 BMW 318SE). Sometimes I fix something but curiously, sometimes it goes out on its own. Looking at the manual, you soon realise the light is a catch-all for “there’s something wrong with your engine” and it’s not actually that specific. Luckily, I have some diagnostic kit and can read the error codes. But in this case, the only fault registering was in German (as it’s a BMW) “prüfung kraftstoff-versorgungssystem” and translated into an equally vague “Fuel supply system”. Great.
Recently I needed to fill up with petrol. I decided to fill up with the ‘good fuel’ – the better of the two at the pump at least. 3 days later, the light went out. Interesting. I did a little research and discovered that many cars older than maybe 8-10 years have their engine management set in a time when fuel had slightly different additives and mixtures. In this case, less ethanol. So your engine’s on-board emissions check is expecting one thing but reading another, even though the engine runs as expected. That’s often enough to cause the engine light to come on.
A little more research dug up a bunch of articles on cheap supermarket fuel being a big culprit. I had a palm/face moment when I remembered I already tried this cheap fuel/expensive fuel test a few years back but the results weren’t clear. Turns out cars are one step ahead and have an in-built sanity check to avoid knee-jerk reactions. They require the car to be run through a certain ‘basic drive cycle‘ before resetting any error codes. In short, you may need to wait a few days or weeks to see that pesky light react.
So, before you spend a bunch of cash on a garage, try filling up with the expensive fuel, give it a few drives and see what happens. And as a rule, definitely avoid supermarket fuel. When you dig a little deeper, you realise forums are awash with that nugget of advice. Good luck!