BMW 7 Series: System Components

Radar Sensors

Two radar sensors are fitted in the vehicle for the Active Blind Spot Detection system. The two parts are different, although visually they look the same.

There is a master sensor that is always fitted in the rear of the vehicle on the right-hand side, as well as a SWW2 that is fitted in the rear left-hand side.

The identical features of the master and SWW2 will be introduced first. Then the special features and differences between the master and SWW2 will be described.

Common Features of the Master and SWW2

The sensors of the Active Blind Spot Detection system work according to the RADAR principle (radio detection and ranging). They have some features in common, but also some differences in comparison with the short-range radar sensors for the ACC Stop&Go function. These are listed in the following table.

MASTER AND SWW2 CHARACTERISTIC REFERENCE CHART

(1) Characteristic signal segment with changing frequency

The RADAR principle offers basic advantages with regard to the detection reliability of road users in poor weather conditions. Only when it is exposed to extreme conditions, for example heavy rain or snow, can a reduction in its range occur. If the sensors detect a particularly extreme situation, this status is signalled, so that the function can be switched off and the driver informed.

Both sensors have the functionality of control units. This means that they are compatible with diagnostics and can be programmed and coded.

The sensors are fitted in the rear of the vehicle above the bumper bracket. They are fitted to a large plastic component that is referred to as the "center guide". From the outside the sensors are not visible, because they are hidden by the bumper trim.

Fig. 87: Overview And Installation Location Of Radar Sensors

RADAR SENSORS LEGENDS

1. Detection zone of the SWW2
2. SWW2
3. Center guide
4. Master
5. Detection zone of the master
6. Symmetrical axis of the SWW2
7. Symmetrical axis of the master
8. Vehicle longitudinal axis
9. Horizontal angular width of beam

As you can see from the graphic, the detection zones of the two sensors overlap. The data on road users that have been detected can therefore not be evaluated separately from each other (for the left and right side of the vehicle). Instead the data is first collected from both sensors and evaluated. Then a decision is made whether the driver must be warned or not.

A detailed view of the installation locations of the master and SWW2 can be seen in the following:

Fig. 88: Identifying Radar Sensor, Centre Guide, Wiring Harness Connector With Mounting Bolts Of Master

RADAR SENSORS LEGENDS

1. Radar sensor for Active Blind Spot Detection (master)
2. Mounting bolts
3. Center guide
4. Wiring harness connector

The fixtures for the sensors do not permit any mechanical adjustment. Instead of the sensors being mechanically adjusted (as is the case with the long-range area sensor in the ACC), they are calibrated using software. When this is done, the actual installation position and above all the alignment of the center axes of the sensors are determined and stored in the sensors. For details please see the section entitled "CALIBRATING THE RADAR SENSORS".

Fig. 89: Identifying Radar Sensor, Centre Guide, Wiring Harness Connector With Mounting Bolts Of SWW2

RADAR SENSORS LEGENDS

1. Radar sensor for Active Blind Spot Detection (SWW2)
2. Mounting bolts
3. Center guide
4. Wiring harness connector

RADAR SENSORS LEGENDS

1. Radar sensor (SWW2)
2. Bracket for shielding
3. Deformation element

Fig. 90: Identifying Radar Sensor, Bracket For Shielding And Deformation Element

Two brackets are fitted to the deformation element of the rear bumper that act as a shield for the radar sensors.

This prevents malfunctions when processing radar signals that could be caused, for example, by reflections from the road surface. The material used for the bracket was specially selected for this intended use. Therefore, in the event of damage to the brackets, they must be replaced with the correct new part.

Emergency repair using a different plastic part is not permitted. Both radar sensors have a similar structure. The connector and the electronics board are located on the lower section of housing. It is used both for electrical shielding and for dissipating heat.

The board always has a signal processor. This evaluates the radar signals and uses them to generate a list of the objects detected by the sensor. The list contains the distance to each object in a longitudinal and lateral direction and the relative speed. In addition, information is supplied about whether the object is in the blind spot area.

The radar front-end (radome) is used to generate and send radar waves. Of course, the receive circuit is also integrated in it. Sending and receiving is carried out via a planar antenna. The radar waves are transformed into the required shape using the so-called radome.

The plastic radome therefore determines exactly the extent of the detection zone of the sensors. The bumper trim also influences the shape of the detection zone. Calibration must therefore always be done with the bumper trim mounted. If done without the bumper trim, different values are assigned to the measured distances. The measuring result would be distorted and the warning for the driver inappropriate.

The radome and the lower section of housing are cemented together. Repairs to the inside of the sensor are not intended. If the test plan of the diagnostic system requests it, then the sensor must be merely replaced in its entirety.

Fig. 91: Side View Of Radar Sensors

RADAR SENSORS SHIELD LEGENDS

1. Outside view of the SWW2
2. Outside view of the master
3. Inside view of the SWW2
4. Inside view of the master

1. Radome
2. Lower section of housing, SWW2
3. Lower section of housing, master
4. Connector
5. Pressure-compensating element, SWW2
6. Mounting eye for the SWW2
7. Mounting eye, master
8. Pressure-compensating element, master

On one side of the lower section of housing, there is an element for producing pressure compensation both on the master and the SWW2. This element contains a membrane with a Teflon coating that is permeable to air and moisture. However, water in liquid form can not permeate the membrane. Pressure compensation is required, because the sensors heat up considerably during operation as a result of electronic power conversion.

Both sensors have an identical looking connector. Even the mechanical encoding of the connector on both sensors is identical. However, the pins are wired differently for master and SWW2. This is why they should only be connected to the intended wiring harness.

How can you distinguish between master and SWW2 then?

Fig. 92: Upper And Lower Section Of Radar Sensors For Blind Spot Detection System

RADAR SENSORS LEGENDS

1. Upper section of the SWW2
2. Upper section of the master
3. Lower section of the SWW2
4. Lower section of the master

1. Labelling "SWW2"
2. Labelling "master"

The mounting eyes of the lower housing sections on the master and SWW2 are located in different positions.

The fixtures for the mounting bolts on the "Center guide" are appropriately positioned. This ensures that the master is mounted only on the right and the SWW2 on the left. Only after installation is complete is it recommended to connect the wiring harness to the sensors.

You can also differentiate between the sensors by using the part number and by the labelling on the lower section of the housing.

Special Features of the SWW2 Radar Sensor

The SWW2 only provides information about the road users in its detection zone. This is why the SWW2 contains only one signal processor for controlling the radar front-end and for evaluating the radar signals. A CAN controller is used to send the data to the master.

The signal processor is also capable of executing the self-diagnostics of the sensor. If SWW2 faults are detected, they are stored in its own EEPROM. They are also transferred to the master and stored there in its fault code memory.

Special Features of the Master Radar Sensor (SWW)

The master performs the same basic tasks as the SWW2 with regard to recording and evaluating data from road users. In addition, the master calculates whether a traffic scenario exists that could be dangerous in the event of a lane change. This calculation is based on data about the road users detected and the state of motion of your own vehicle. If such a situation is detected, the master sends a corresponding signal via FlexRay to the ICM control unit. In addition, the master uses the same path to send signals about the status of both sensors, for example to determine whether they are functioning correctly or there is a fault.

The master executes self-diagnostics in the same way as the SWW2. If, in the process, it detects a fault within itself or a fault is registered by the SWW2, an entry is made in the fault code memory of the master. This makes it possible to read faults with the SWW2 during servicing, even though the diagnostic system is only communicating with the master and as a result is only accessing its fault code memory.

The master contains in addition to the signal processor a further microprocessor for this purpose. This also carries out communication via the FlexRay controller with partner control units, and with the ICM control unit in particular.

Bus Connections

The sensors for Active Blind Spot Detection are connected with two bus systems:

• The master (SWW) is connected to the FlexRay and to the local CAN.
• The SWW2 radar sensor is only connected with the local CAN.

The SWW2 uses the local CAN to transmit the data of all of the road users it has detected to the master. The sensors also utilize the local CAN to exchange internal system status and control signals.

The local CAN is physically set up like the PTCAN and therefore works at a bit rate of 500 kBit/s. Master and SWW2 each have one of the two terminal resistors, each with 120 ohms.

The FlexRay represents the interface between the sensors and the whole vehicle. In this way, the sensors, or to be exact, the master sensor, receives the data about the state of motion of the vehicle (e.g. the road speed and yaw rate).

The master uses this interface to send information about whether the necessity for a warning exists to the ICM control unit.

The FlexRay is routed to the master and is fitted there with a terminating resistor. The master is therefore a terminal node in the FlexRay network.

A detailed description of new features in the FlexRay network can be found in the F01/F02. bus systems training material in ICP and TIS.

Voltage Supply

The SWW sensors are supplied with power via a common fuse with terminal 15. The fuse is located in the rear fuse carrier (in the luggage compartment). The voltage supply is routed to the master and from there to the SWW2.

The wake-up line is therefore not required on the SWW sensor

NOTE: During the overrun of terminal 15 the SWW sensors save important data in the integrated EEPROM. This includes, for example, fault code memory entries and values calculated during calibration. This data is permanently stored and available again for the next driving cycle. It is therefore important to wait for the overrun from terminal 15 when work is carried out on the SWW sensors, before disconnecting the voltage supply (connector, battery).

Fig. 93: Bus Systems And Voltage Supply To Radar Sensors Of Blind Spot Detection System

RADAR SENSORS LEGENDS

1. SWW2 radar sensor
2. Master sensor
3. Feed line and continuation of the voltage supply (terminal 15 and ground)
4. Local CAN feed line with a terminating resistor
5. FlexRay feed line with a terminating resistor
6. Voltage supply feed line (terminal 15 and ground)
7. Fuse for SWW sensors (rear fuse carrier in the luggage compartment

Calibrating the Radar Sensors

The calibration process is carried out with use of the ISTA diagnostic system. Calibration is performed for both sensors of the Active Blind Spot Detection system successively.

Reasons for calibration

The radar sensors of the Active Blind Spot Detection system measure the position and speed of road users approaching from the rear. This measurement is taken by the sensor housing as a reference value. In order to make a decision as to whether the driver should be warned or not, the measured data must be related to the vehicle's coordinate system. For this the exact location of the sensors must be known.

The installation location of the sensors is principally specified by the position of the retaining bore in "center guide". However, the sensor may be incorrectly aligned during installation or as a result of the tolerances of supporting parts. This applies in particular to the angle formed by the sensor axis and the vehicle longitudinal axis. If the deviation between the actual angle and the angle specified in the design is too large, this would interfere with the proper functioning of the Active Blind Spot Detection system. Warnings would either be omitted or be produced inappropriately.

The radar sensors must always be calibrated after the following:

• At least one of the radar sensors has been replaced.
• The bumper trim has been replaced.
• Repair work to the supporting parts has been carried out (e.g. to the "center guide").
• The test plan of the diagnostic system requests this due to a fault code memory entry.

Special Situations and Fault Statuses

Communication faults and internal control unit faults are not dealt with here in detail. Problem resolution is carried out in the same manner as with other control units, i.e. with the assistance of the test plan in the diagnostic system.

Instead, the emphasis here is on the statuses which apply specifically to the radar sensors of the Active Blind Spot Detection system. The material presented here should facilitate the diagnostics.

Blindness

"Blindness" here is used to denote heavy interference with the radar sensors, in which they no longer are able, for example, to detect road users at the required range. Blindness can also cause incorrect or omitted warnings.

The radar sensors contain a function which enables it to detect this status during operation. In this case, the master sends a bus signal to the ICM and the Active Blind Spot Detection system is then deactivated. The driver is informed about this by a Check Control message. The blindness status is documented with an entry in the fault code memory for a subsequent workshop visit.

Possible causes of the blindness status are:

• The sensor is covered by a sticker or by a bicycle carrier at the rear.
• Deformation (dents) in the bumper trim, even if for instance it has been repaired with plastic filler.
• Incorrect vertical alignment of the sensors (e.g. upwards) through a deformation of the supporting parts.
• Extremely thick covering of snow/slush on the bumper trim.

Errors in the sensor alignment

In the radar sensors of the Active Blind Spot Detection system, a function is calculated that can detect sensor alignment errors when the vehicle is in motion. This function monitors the data about detected objects as it is processed.

If the detected sensor alignment error is within a range that is still tolerable, the function compensates for the error. This means the data about the detected road users is corrected by the known value. If a sensor alignment error that is too large is detected, the proper functioning of the Active Blind Spot Detection system is no longer possible. The master then sends a signal to the ICM and the Active Blind Spot Detection system is switched off.

The driver is informed about this by a Check Control message.

Reasons for deactivating the system due to detected sensor alignment errors include:

• A new radar sensor was installed without being calibrated (detected immediately).
• The sensor is covered by a sticker or by a bicycle carrier.
• Mechanical damage to the rear of the vehicle with deformation of the supporting parts (e.g. the "Center guide").
• Deformation (dents) in the bumper trim, even if for instance it has been repaired with plastic filler.

Some of the reasons given here could also apply to the "blindness" status. For example, depending on the extent of the deformation of the bumper trim, this can result in blindness.

This kind of deformation can distort the radar signals in such a way that the sensors detect a sensor alignment error.

Rear damage

Two kinds of damage are plausible which require different repair measures:

• Damage exclusively to the bumper trim in the area where the sensor is installed.
• Additional deformation of the bumper bracket or other supporting parts.

Damage to the bumper trim

Of course only damage in the area where the radar waves are emitted from the sensors are relevant. If the bumper trim is deformed there, scratched extensively or it has an uneven thickness due to repairs to the plastic, can interfere with the proper functioning of the radar sensors. Bumper stickers placed over the area can also cause radar interference.

These situations may result in a reduced range, the omission of warnings or the incorrect production of a warning.

In the event of this kind of damage, you must ensure that the sensor installed behind the bumper trim has not been damaged in any way.

The repair entails restoring the original position and the original shape of the bumper trim to ensure proper system operation.

NOTE: The US marketing term for Lane Change Warning System (SWW) is Active Blind Spot Detection. These two systems are one and the same and are not to be confused with Lane Departure Warning.

Damage to supporting parts

If a supporting part (e.g. the bumper bracket or the trunk trim fitted to the "Center guide") is deformed, the sensors for the Active Blind Spot Detection system are probably no longer correctly aligned. This leads to the omission of warnings or that warnings are incorrectly produced.

Your first option is to attempt a calibration. To do this, the bumper trim must be mounted. If the calibration is performed successfully, the misalignment was so small that it could be compensated for in the calibration (using software).

If the calibration produces a deviation in the sensor alignment that is larger than specified by the design, the "center guide" must be correctly realigned. Because the "center guide" acts as a carrier for the sensors, aligning the "Center guide" also repositions the sensors correctly. This process is described in detail in the Repair Instructions.

Based on the spacers that act as gauges, the correct alignment can be restored. In any case, after this kind of body repair, the sensors will have to be calibrated.

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