System functions

The Run Flat Indicator (RPA) comprises the following functions:

• Self-test
• Initialization
• Detects drop in tire pressure
• Visual and acoustic warning
• Actively reduce the load on the defective wheel (E70 only)

Self-test 

The RPA performs a self-test when terminal 15 is switched ON. A fault in the RPA is indicated by the RPA indicator and warning light and by a symbol in the LCD display.

Initialization 

Initialization is started manually (e.g. by pressing the RPA button). Once it has been started, initialization will continue through to complete calibration. This process may be interrupted any number of times.

It is important that the vehicle is driven away immediately after initialization is started. The system will not start calibration until the vehicle is driven away. Even a terminal change will not change this.

In principle, calibration is only possible while the vehicle is being driven (road speeds above 25 km/h).

Initialization will run as a fully automatic calibration sequence (after the journey has started). In other words, the circumference of individual tires are recorded and evaluated.

To allow a drop in tire pressure to be detected, the system considers different speed ranges and driving situations. Taking account of the driving situation means that the system has to be primed for each speed range individually.

From 09/2004 (starting with E87), these speed ranges and driving situations have been combined into 3 calibration ranges. This means greater clarity for output via the BMW diagnosis systems Group Tester One (GT1) and DISplus.

The initialization phase lasts approx. 5 to 15 minutes for the individual speed ranges. The end of the initialization phase is not indicated.

A visual and acoustic warning can only be emitted in the speed ranges that have been calibrated by at least 67 percent.

The calibration process can be delayed by:

• dynamic driving
• a road with lots of bends
• frequent changes in load (only on vehicles with electronic height control -> air spring/height control regulation)

Detects drop in tire pressure 

The RPA records the wheel speeds using the wheel-speed sensors from the DSC. The RPA compares the speeds of the individual wheels and computes an average speed. In this way the RPA is able to detect a loss of tire pressure. (In the event of a tire losing pressure, the tire rolling circumference of the affected tire is also reduced.)

Visual and acoustic warning 

A drop in pressure in one tire of approx. 30 % ± 10 % from the initial value is indicated by the RPA indicator and warning light. In addition, an acoustic signal sounds.

Signal output: Depending on the model concerned, either via the instrument cluster or the multi-audio system controller (M-ASK) / Car Communication Computer (CCC).

Actively reducing load on defective wheel 

• E70

If the RPA detects a flat tire on one of the rear wheels, the electronic height control will actively reduce the load on the wheel concerned. The body will then assume a slightly inclined attitude. As soon as the flat tire has been repaired and the RPA reinitialized, the inclined attitude will be levelled out again. No work is needed on the air suspension itself.

Special conditions for system function 

The following driving conditions  may cause a delay in the warning  being given in the event of a drop in tire pressure:

• Heavy braking
• Rapid acceleration
• High rate of lateral acceleration
• Cornering (in a tight corner)
• Vehicle speed dropping below a minimum speed (the RPA only responds when a certain minimum speed has been reached)
• Large difference in slip (between axles or between wheel on one side of vehicle)
• Initialization not being completed in current speed range (see "Controls")
• Winter conditions
• Heavy changes in load (only vehicles with electronic height control)

The following operating conditions  may cause a delay in the warning  being given in the event of a drop in tire pressure:

• Driving with snow chains fitted

  Driving with snow chains may impair the correct function of the RPA.

  The system will work as normal again after the snow chains have been removed and the vehicle is driven for a few minutes. (Repeat initialization not necessary.)

  NOTE: Do not perform initialization when snow chains are fitted. 
  Initialization and snow chains will cause incorrect adaptation values.
• Trailer towing

  Initialization should be performed when a trailer with a weight greater than approx. 300 kg is being towed.

  Repeat the initialization process after detaching or unloading the trailer.

• Old/new tires
  NOTE: Only fit tires with the same tread depth! 
  Avoid fitting tires with greatly different tread depth (from approx. 2 millimeters) on one axle. The different diameters mean that the correct operation of the RPA is no longer guaranteed.

The following situations may cause unnecessary warnings  :

• Initialization not completed after a tire has been replaced (old/new tires, summer/winter tires, change in direction of rotation, or replacement of single defective tire) tire pressures have been changed
• Tires have different levels of wear
• Frequent changes in load (only on vehicles with electronic height control)
• Tires that have not been approved by BMW
• Damaged tires, even if no loss of pressure can be detected (e.g. spin imbalance)
• Tire has changed slightly during the running-in phase (settling)

In the following cases, the system will not emit a warning despite a drop in tire pressure being detected : 

• The same amount of pressure is lost in 2 or more tires.
• Drops in tire pressures caused by diffusion and affecting all 4 tires equally
• If a tire is damaged with a sudden loss of all pressure (tire blow-out, warning is given too late)

Operation 

The Run Flat Indicator (RPA) is initialized using the following control elements:

• RPA button
• On-board computer button on turn-signal/main-beam switch
• With iDrive in the Central Information Display (CID) with the controller

Initialize the RPA in the following situations:

• If tire pressure is changed (tire pressure is corrected or reset)
• If the position of the tires is changed (change of axles, wheels), even if the tire pressure is not changed
• If a tire is changed or the wheels are interchanged

  (e.g. old tires for new tires, summer tires for winter tires, etc.)

Start initialization as follows:

• Terminal 15 ON

  (engine OFF or ON, do not pull away)

• Vehicles with  RPA button
  • Press and hold the RPA button until the RPA indicator and warning light lights up yellow for a few seconds
• Vehicles with  BC button (on-board computer function)
  • In the on-board computer function select "RPA" and "INIT" (LCD display) with the rocker switch on the turn-signal/main-beam switch. Press the BC button to confirm.
  • Press and hold the BC button for approx. 5 seconds, until a box with a tick appears behind the "INIT" display.
  • R56:
    • In the on-board computer function select "SET/INFO" (LCD display in auxiliary instrument) with the BC button on the turn-signal/main-beam switch.
    • Press and hold the BC button until the display changes
    • Press the BC button repeatedly until the corresponding symbol and the word "RESET" are displayed.
    • Press and hold the BC button until a square with a tick appears.
• Vehicles with Central Information Display

  Initialization is performed via the Central Information Display (CID) and controller.

  • Select "RPA" in the "Settings" menu and confirm.
  • Select "Set" and confirm.
• Drive off

The end of the initialization phase is not indicated.