Can you take a pic of the warning next time it comes on? I ask because my (indirect) tire pressure warning light is
yellow (not red). It even says in the owners manual that the light is yellow.
If you have a red light coming on...double check in the owners manual to see if the warning light is actually for the flat tire monitoring system...and not for some other reason.
Taking a pic of the light may also reveal if there's any differences between BMW markets...perhaps your Hong Kong market has a different warning light than here in the USA.
The chart below that details the difference between the direct & indirect tire monitoring systems BMW used during the production of the e53 X5...also shows that both direct & indirect systems uses a
YELLOW tell tale warning light:
