Run Flat Indicator; All models: Notes

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Fig 1: Identifying Run Flat Indicator (RPA) Monitors

Courtesy of BMW OF NORTH AMERICA, INC.

Introduction

The Run Flat Indicator (RPA) monitors the tire pressure throughout the journey.

The entire vehicle weight is carried by the air pressure in the tires. If the pressure in one of the tires should drop, the tire will gradually "cave in". The resulting flexing means that the defective tire will quickly receive additional damage. The tire could burst.

Some 80 % of all flat tires are caused by small holes (e.g. caused by nails). The holes result in a gradual loss of pressure in the affected tire. Many "tire blowouts" can be traced back to preliminary damage caused by a gradual loss of pressure.

A gradual loss of pressure in one tire may remain unnoticed for a long time. The lack of pressure only makes itself clearly felt when driving when the tire is almost completely empty.

As tire pressure drops, the radius of the wheel and with it the tire's rolling circumference will also decrease. The upshot is that the wheel speed of the affected tire is increased.

The RPA records the wheel speeds using the wheel-speed sensors of the Dynamic Stability Control (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.

The RPA detects a drop in pressure below about 30 % ± 10 % of the initial value. The RPA indicator and warning light indicates a drop in tire pressure. The RPA will indicate this after just a short distance, as a rule after a few minutes, from a certain minimum speed (e.g. 25 km/h) up to the permissible top speed.

Different control units for the Run Flat Indicator
E46 All-wheel drive
E46, E53, E83, E85, E86
E60, E61, E63, E64
E65, E66
E70
E87, E90, E91, E92, E93
R56

Despite coming from different manufacturers the systems hardly differ from one model series to the next in the way they appear to the driver (initialization, RPA indicator and warning light, characteristics, diagnosis).

IMPORTANT: Responsibility resides with the driver at all times
Check tire pressures regularly, at least twice a month and before embarking on lengthy journeys. During initialization, the set tire pressure is taken as the initial value for the current set of tires.
If all 4 tires loose pressure at the same rate, the wheel speeds will also change at the same rate. The RPA is unable to detect a uniform drop in pressure in all tires (e.g. due to diffusion = natural loss of air from all 4 tires)

IMPORTANT: Correct function of the Run Flat Indicator is not guaranteed when the emergency wheel is fitted.
As the emergency wheel has a much smaller diameter, the correct operation of the RPA can no longer be guaranteed.

Brief description of components

The SMG system comprises the following key components:

4 wheel-speed sensors
The wheel-speed sensors of the Dynamic Stability Control (DSC) measure the wheel speeds of the individual wheels.
RPA button
- E46, E53, E83, E85, E86
The RPA button is only needed for initializing the PRA.

(RPA initialization means "teaching the system the tire pressures").
CID: Central Information Display
Vehicles that are equipped with CID are initialized using the CID.
On-board computer button and rocker switch on turn-signal/main-beam switch
- E87, E90, E91, E92, E93, R56
Initialization is performed on the LCD display, using the BC button and the rocker switch on the turn - signal/main-beam switch. The on-board computer functions are selected with the rocker switch.

The R56 does not have a rocker switch. The on-board computer functions are selected with the BC button.

The RPA software is in the following control units, depending on model series:

RPA control unit
- E46 all-wheel drive
The E46 All-wheel drive has a separate RPA control unit.

The 4 wheel-speed sensors measure the wheel speeds. The DSC control unit sends the signals through 4 direct wires to the RPA control unit.

Alternatively
ABS control unit with additional software for Run Flat Indicator
- R56
The ABS control unit is standard equipment on the R56. RPA is integrated into the DSC control unit by means of additional software.

Alternatively
ASC+T control unit with additional software for Run Flat Indicator
- R56
ASC+T is special equipment on the R56 (ASC+T: Automatic Stability Control plus Traction). RPA is integrated into the ASC+T control unit by means of additional software.

Alternatively
DSC control unit with additional software for Run Flat Indicator
- E46, E53, E60, E61, E63, E64, E70, E83, E85, E86, E87, E90, E91, E92, E93
- R56: Optional equipment
With the DSC Mk60 and DSC 8, the RPA is integrated in the DSC control unit using additional software (The E70 is equipped with DSC 8 Premium).

Alternatively
CIM: Chassis Integration Module
- E65, E66
The CIM controls:
- Servotronic
- Steering column adjustment
- Run Flat Indicator (RPA)

The following control units are involved in the Run Flat Indicator system (in alphabetical order):

CAS: Car Access System
- E60, E61, E63, E64, E65, E66, E70, E87, E90, E91, E92, E93, R56
The CAS control unit provides input signals relating to terminal status (e.g. terminal 15 ON).
GM: General module
- E46, E53, E83, E85, E86
The general module provides input signals relating to terminal status (e.g. terminal 15 ON).
JBE: Junction box electronics
- E70, E87, E90, E91, E92, E93, R56
The JBE is the data interface (= gateway) between the K-CAN and the PT-CAN. (K-CAN stands for "Body Controller Area Network"; PT-CAN stands for "Powertrain Controller Area Network")

The junction box consists of the junction box electronics and the electrical distribution center.
KGM: Body gateway module
- E60, E61, E63, E64 from 09/2005
The body gateway module (KGM) replaces the safety and gateway module (SGM).

The KGM forms the data interface (= gateway) between the K-CAN and the PT-CAN.
M-ASK or CHAMP or CCC: Multi-audio system controller or multimedia platform or Car Communication Computer
M-ASK or CCC or CHAMP (multimedia platform: CHAMP; Central Head Unit and Multimedia Platform) issues an acoustic warning through the loudspeakers if the tire pressure should drop.

(On vehicles without M-ASK or CCC or CHAMP, the instrument cluster will emit the warning.)
SGM: Safety and gateway module
- E60, E61, E63, E64 up to 09/2005
- E65, E66 from 03/2004
The SGM is the data interface (= gateway) between the K-CAN, byteflight and the PT-CAN.
SZL: Steering column switch cluster
- E87, E90, E91, E92, E93, R56
The signals from the on-board computer button and from the rocker switch are recorded and processed in the SZL. The data is transmitted to the instrument cluster (on-board computer).
ZGM: Central gateway module
- E65, E66 until 03/2004
The ZGM forms the data interface (= gateway) between the K-CAN and the PT-CAN.
KOMBI and CID: Instrument cluster and Central Information Display
A fault in the RPA or drop in tire pressure will be indicated by the RPA indicator and warning light in instrument cluster.

At the same time, the symbol will light up in the LCD display.

Faults registered by the RPA are indicated as follows by the RPA indicator and warning light (for variations, please refer to national version):
- The RPA indicator and warning light lights up:
  - Red (with acoustic signal):
    Drop in tire pressure more than approx. 30 % ± 10 %.
    
    Driving safety is no longer guaranteed.
  - Yellow:
    RPA failed

Information about the check control message can be called up in the CID (CID is fitted depending on the vehicle's equipment).