System function of RDC: Notes

The Tire Pressure Monitor (RDC) is a system for monitoring the tire pressure when driving. It is offered exclusively in the USA (legal requirement) and as an optional extra in Canada.

The tire inflation pressure to be monitored is specified by the driver. He or she instructs the system via the control function in iDrive to save the current tire inflation pressure as the target pressure value (Reset). The plausibility of the setpoint value is checked before the RDC control unit adopts it (axle-wise comparison of the nominal pressures, minimum pressures). A reset is only possible when the tire pressure on all wheels is at least 1.6 bar. If the tire pressure of one wheel falls below this limit, a Check Control message is issued immediately. If the pressure difference between the wheels on one axle is > 0.4 bar, the reset is rejected following a plausibility check. A Check Control message is output. Remedy: set tire pressures to the correct values and then run the reset once again.

Internal sequence after activated adaptation process (reset):

1. Recognition of the fitted wheel electronics systems
2. Identifying the position of the wheel electronics systems
3. Plausibility check by checking the target pressures
4. Adoption of the specified pressures as nominal pressures

On comparison of the current tire inflation pressure with the target pressure, the air temperature is taken into account. On the basis of the nominal pressure and temperature during the reset, the RDC calculates the limit values for the tire pressure. The tire pressure increases by 0.1 bar per 10 °C increase in temperature. If the temperature-evaluated limit values are not reached, the RDC issues a Check Control message.

Fig 1: RDC Control Unit Communication Diagram

Courtesy of BMW OF NORTH AMERICA, INC.