Well, there's two systems. The first is Flat Tire Monitor (FTM) which uses tire rotational speed obtained from the ABS sensors and compared by the RDW module. The second is an actual Tire Pressure Monitor System (TPMS) that measures tire pressure directly using sensors inside each tire, mounted on the wheel, processed by RDC module. The E39, like mine, and E53 among others have a FTM. Most E70, like mine, have a TPMS but some have a FTM. Any of these sensors or modules can cause a tire pressure warning. Some tire pressure warning issues could exist with other fault indications. Conversely, not all faults with these sensors or modules will result in a tire pressure warning.

Clearly, the first step is determining which system is in use on your X5. If it has a true TPMS, the Autel*MaxiTPMS TS501*can interrogate each sensor and provide the pressure, temperature, battery status and serial number for each sensor (tire) and is what I use. Assuming the sensors are working, additional troubleshooting steps can be taken. If the FTM, proper diagnostic software and terminal will direct the next troubleshooting steps based on the specific faults reported.

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8/2011 X5 xDrive35d Sport, Black Sapphire Metallic, Black Nevada Leather, Fine Burr Walnut Trim
2/2001 M5, Jet Black, Exclusive Complete Black Walk Nappa Point Heritage Leather, Black Cubic Trim