if your X5 cant start or dies after few seconds check fuel. Gauge might be showing wrong LOL it sounds stupid but i had lots of checking and computer diagnostics with different error codes untill I opened tank to check pumo and found that is dry. never had this issue before and i was sure it must be at least 20 liters
little bit off topic but just wanna say never trust gauges it can make u look stupid like i did
Have a nice day