I'd check the resting battery voltage then firstly Phil. If it's significantly below 12v it could be the issue.
Hi TA drives fine so will leave it until it stiops working..
Have had this also with a faulty but still working number plate light bulb.
Possible car back to normal. The triangle could have been error message for post oil change uniair relearn. Though never had anything like this with my 63 plate. Allegedly it can relearn itself. Maybe it's done it. Am back to foot to the floor in it anyway.