Emergency running systems

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2010 BMW 535xi, 2010 BMW 535i, 2009 BMW 535xi, 2009 BMW 535i, and 2008 BMW 535xi. However, it is still accessible from the selected car via links, so may be relevant.

In addition to the warning systems, two emergency running systems are also employed to prevent a depressurized tire from caving in:

Components of emergency running system with self-supporting tires:

EMERGENCY RUNNING SYSTEMS COMPONENTS REFERENCE

RDW (standard equipment)	Tire pressure warning
RDC (available as option from 03/2000)	Tire pressure control
SST	S elf S upporting T ire
EH2 disc wheel	Disc wheel with E xtended H ump 2

Components of emergency running system with integrated support ring:

EMERGENCY RUNNING SYSTEMS WITH INTEGRATED SUPPORT RING COMPONENTS REFERENCE

Support ring	NOTE: In the future, only for heavy safety vehicles (E38/3)
RDC (optional)	Tire pressure control
H2 disc wheel	Standard disc wheel with H ump 2

Tire pressure control (RDC)

RDC system description

RDC permanently monitors the tire pressure and the temperature in the tires, both while the vehicle is being driven and when it is stationary. Data is transmitted via data telegram by the wheel electronic units to the antennas installed in the wheel housing and on to the RDC control unit. There, the data received is compared with the stored limit values.

After correcting the air pressure with the engine off and the ignition on, press the Set button and hold (approx. 6 seconds) until the words "Set tire pressure" appear in the instrument cluster (instrument cluster high) or the yellow LED lights up (basic instrument cluster).

If the limit values are exceeded, the driver will be warned via the instrument cluster in two stages, as follows:

Tire PRESSURE LOSS VALUE

Loss of tire pressure	Warning
Drop in tire pressure of 0.2 to 0.4 bar	Yellow LED on basic instrument cluster or Text: "Check tire pressure" on instrument cluster high Gong: no
Drop in tire pressure of more than 0.4 bar	Red LED on basic instrument cluster or Text: "Tire failure" on instrument cluster high Gong: yes

Advantages of RDC

RDC ADVANTAGES REFERENCE

1. Safety	early warning in the event of rapid loss of pressure warning of loss of tire pressure through normal diffusion
2. Comfort	unchanging ride comfort instruction to check tire pressure as necessary
3. Service life, economy	minimization of tire wear minimization of fuel consumption
4. New developments	allow tires with emergency running characteristics to be fitted no spare wheel if tires with emergency running characteristics are fitted (saves weight)

RDC system layout

Fig 1: RDC System Layout Diagram

Courtesy of BMW OF NORTH AMERICA, INC.

RDC control unit
Wheel electronic units (4 off)
Wheel electronic unit for spare wheel (optional)
Receiving antennas (4 off)
Set button
Display element
Anti-theft warning system
- Wiring harness

Component description

RDC control unit

Fully diagnosis-compatible

Task:

evaluates the following telegrams from the wheel electronic units:

tire pressure
tire air temperature
identification number (ID) of wheel electronic unit
remaining service life of wheel electronic unit battery

Fig 2: Identifying RDC Control Unit
Courtesy of BMW OF NORTH AMERICA, INC.

If required, information or a warning is transmitted.

Wheel electronic unit with valve

Components:

pressure sensor
temperature sensor
transmitter
- frequencies according to country
power supply
- service life: approx. 7 years
- not exchangeable
  
  Fig 3: Identifying Wheel Electronic Unit With Valve
  Courtesy of BMW OF NORTH AMERICA, INC.

Installation location of wheel electronic unit in disc wheel

The wheel electronic unit (1) is screwed to the valve (2) on the disc wheel (3)

Identifying feature:

metal tire valves

NOTE: Different valves have to be used to allow for the different disc wheel sizes. The valves are color-coded. The correct coding can be taken from the spare parts catalogue.

Fig 4: Identifying Installation Location Of Wheel Electronic Unit In Disc Wheel

Courtesy of BMW OF NORTH AMERICA, INC.

Antenna

There is an antenna in each wheel housing.

Task:

receives telegrams and forwards these to the RDC control unit.

Fig 5: Identifying Antenna

Courtesy of BMW OF NORTH AMERICA, INC.

Component description

Set button

Installed in the instrument panel to the right of the steering wheel. (E46: in the center console)

Symbol: tire cross-section

Task:

initialization after resetting cold tire pressure or after changing tire or wheel location.

Fig 6: Locating Set Button

Courtesy of BMW OF NORTH AMERICA, INC.

Display element in instrument cluster

Indicator lamp lights up yellow:

drop in tire pressure of 0.2 to 0.4 bar Indicator lamp lights up red:
drop in tire pressure greater than 0.4 bar

Fig 7: Locating Display Element In Instrument Cluster
Courtesy of BMW OF NORTH AMERICA, INC.

Tire pressure warning RDW

RDW system description

RDW measures the wheel speeds on all four wheels, using the wheel speed sensors of the ABS/ASC or ABS/DSC system. It compares the wheel speeds of the diagonally opposite wheels and of the average speed.

In the event of a drop in tire pressure, the dynamic diameter of a wheel will change, leading to a changed wheel speed.

A drop in tire pressure of 30 ± 10 % can be detected on all wheels from about 15 km/h (10 mph) up to the vehicle's top speed.

If this value is exceeded, the driver will be warned via the instrument cluster as follows:

Tire PRESSURE LOSS VALUE

Loss of tire pressure	Warning
Loss of tire pressure of 30 ± 10 %	Red LED Text: "Tire failure" Gong: yes The vehicle is not to be driven faster than 80 km/h (50 mph). NOTE: A cautious driving style with moderate forward and transverse acceleration will help to prolong the service life of the defective tire.

Advantages of RDW

With two exceptions, the advantages of RDC also apply to RDW.

Exceptions:

no warning of loss of tire pressure through normal diffusion
tire pressure still have to be checked regularly, every 14 days

RDW system layout

Fig 8: RDW System Layout

Courtesy of BMW OF NORTH AMERICA, INC.

Wheel speed sensors of ABS/ASC or ABS/DSC system
ASC = Automatic Stability Control

DSC = Dynamic Stability Control
RDW control unit
Set button
Display element
- Wiring harness