There may be some confusion around the acronyms in different parts of the world. In North America, the tire pressure monitoring system uses wheel speed sensors, and is commonly referred to as TPM. That is the one you are referring to as RDC. It should be a fairly simple retrofit, assuming your vehicle had it as an option originally. Search on TPM to see related posts, or if anyone on the board has done it. The sensors are the standard DSC/ABS sensors. There is a button to reset it, and likely a module to add the logic to the vehicle.

In North America, RPA can stand for Remote Parking Assist, also known as PDC or Park Distance Control. What you are referring to as RPA is a system that has pressure sensors in each wheel, whatever it is called by BMW. It is not available in North America, as I understand it. It is also available from the aftermarket (Tirerack.com sells one, so do other tire stores) as well as BMW, outside of North America (for certain models). The advantage of this system is that if your tires slowly lose pressure over time, the wheel speed sensors won't pick it up, because they measure the rotational speed difference between each tire. The pressure sensor will pick up a slow pressure drop, if it crosses the threshold pressure setting. Having said that, I am not sure that it is really necessary in a road vehicle. I have some experience with this type of system in off-road heavy equipment tires, but in that case the price of a low pressure or flat tire is much higher because tire repair costs are insignificant compared to the costs of machine downtime.

I would invest in a good manual tire pressure gauge, and make it part of your regular vehicle check. If the wheel speed sensor system was an easy upgrade, that would be the only one I would consider. I have that system on my Z4, but it has provided no value to me yet. The slow and relatively equal pressure drop over time isn't caught by that system (see note above) and it is really just there as a safety net for the run-flat tires, to let you know that you are 'running flat' as it were.

Jeff

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue