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Self Study Programme 620 For internal use only Audi ACC Systems Audi Service Training Adaptive Cruise Control (ACC) systems Recent years have been characterised by rapid development in the field of driver assist systems This has been made possible by technological progress, specifically in the development and production of electronic components The complexity of available functions is also growing due to the shared use of subfunctions by various vehicle systems, as well as by increasing information exchange between vehicle systems It is predicted that piloted driving will become a technical reality even during this decade Adaptive Cruise Control (ACC) is one of the basic systems which laid the foundation for this development when it was first introduced on the Audi A8 in 2003 In the course of this evolutionary process, the range of functions of the ACC system has steadily grown and this system is today used in many current Audi models A self study program (SSP 289) was previously published when the ACC system was introduced on the Audi A8 in 2003 The range of functions of ACC has since been significantly extended by, in particular, including measured data provided by other sensors Further system improvements have extended the system's limits and greatly increased system availability This self study programme serves as an update to the existing SSP 289 It also provides an overview of the ACC systems used in current Audi models Another key topic is the additional functions complementing the ACC basic function In the area of service, special attention is given to the procedure for setting the current ACC systems with two radar sensors Understanding the functional relationships between systems is a major challenge for service personnel This knowledge is indispensable when it comes to explaining to customers how systems work and performing function tests as well as identifying, diagnosing and, ultimately, correcting faults 620_001 Contents ACC basic function Overview Technische implementation - radar technology The distance measurement process _ Determining the speed of the vehicle ahead Example showing how the speed and distance of the vehicle ahead are determined _ Determining the position of the vehicle ahead 10 Determining the vehicle relevant to ACC _ 11 Adaptive Cruise Control (ACC) - system limitations _ 12 Description of ACC system ACC options 13 System parameters _ 14 System components 16 Networking - data transfer _ 20 Operation and driver information ACC on/off _ 22 Setting the target speed _ 22 Setting the target distance _ 23 Setting the drive program 23 Setting the gong volume _ 24 System status indication _ 24 How the driver is prompted to take over _ 24 Basic operation 24 ACC auxiliary functions Overview _ 25 Audi braking guard 26 Evolution _ 31 Audi Stop and go 32 Lane change assistance _ 37 Service operations Sensor vision _ 39 Replacement and removal/installation of the ACC sender with ACC control unit _ 39 Calibrating the ACC sender _ 40 • The Self Study Programme teaches a basic knowledge of the design and mode of operation of new models, new automotive components or new technologies It is not a Repair Manual! Figures are given for explanatory purposes only and refer to the data valid at the time of preparation of the SSP This content is not updated For further information on maintenance and repair work, always refer to the current technical literature ! Information Reference ACC basic function Overview Adaptive Cruise Control is a systematic further development of the cruise control system first introduced on the Audi A8 in 2003 If the road ahead is clear, ACC acts in much the same way as a cruise control system by adjusting the speed of the vehicle to the target speed set by the driver If it is not possible to travel at the desired speed due to a slower-moving vehicle ahead, ACC maintains the vehicle-to-vehicle distance set by the driver The vehicle is, if necessary, decelerated by reducing engine power, by shifting down into a lower gear (on models with automatic transmission) and/or by applying corrective braking In certain traffic situations, active braking of the vehicle by the driver is still required and indicated by audible and visual warnings No vehicle in front: the vehicle travels at the desired speed Target distance Vehicle ahead travelling slower than the desired speed: the desired vehicle-to-vehicle distance is maintained 620_002 To maintain a constant speed-dependent distance to a vehicle ahead driving in the relevant lane, the ACC control software requires the following information: Distance to vehicle ahead 620_003 Speed of vehicle ahead 620_004 Position of vehicle ahead 620_005 If there are multiple vehicles within the range of vision of the radar, the system utilises the above information to select the appropriate reference vehicle 620_006 Technische implementation - radar technology Radar technology is used to to implement the ACC basic function Radar waves have advantages over optical systems due to their short wavelength Radar waves are absorbed and deflected to a much lesser degree, especially in conditions of impaired visibility (fog, driving snow) As a result, the system provides higher availability than optical systems Radio detecting and ranging (Radar) is an electronic process for determining the position of objects The transmitted radar waves are reflected from suitable surfaces and objects The time span between transmitting the signal and receiving the reflected signal is dependent on the distance from the object The received waves reflected are correlated with the waves transmitted and evaluated The distance measurement process A Transmitter Receiver 50 m B Transmitter Receiver 100 m 620_008 This example shows the dependence of signal travel time on the distance between the transmitter/receiver and object (see diagram): The vehicle-to-vehicle distance in case B is twice that in case A: In case B the time which elapses until the reflected signal reaches the receiver is twice that in case A Direct travel time measurement is a highly complex process For this reason, travel time is measured indirectly in the form of an FMCW (Frequency Modulated Continuous Wave) process Continuously emitted ultra-high frequency oscillations with a time-variable frequency are used as a transmission signal A carrier signal in the frequency band between 76 and 77 Gigahertz acts as a "vehicle" This process eliminates the need for complex direct travel time measurement Instead, the more easily determinable frequency differences between the signal transmitted and the signal received (=reflected) are evaluated Frequency A A Time ± 200 MHz B B The diagram shows the ± 200 Megahertz change in the frequency of the carrier signal due to frequency modulation Frequency-modulated (FM) signal A B A B Time While the amplitude (signal strength ) of the frequency-modulated signal stays almost constant, the frequency (number of oscillations per unit of time) changes At the points in time marked A , the signal frequency in both diagrams has reached the maximum value (greatest number of oscillations per unit of time) At the points in time marked B, the signal frequency is at its lowest (least number of oscillations per unit of time) 620_009 Determining the speed of the vehicle ahead A physical phenomenon called the "Doppler shift" is utilised to determine the speed of the vehicle ahead It makes a difference whether the object reflecting the transmitted waves is stationary or moving relative to the transmitter If the distance between the transmitter and object decreases, the frequency of the waves reflected will increase If the distance increases, the frequency will decrease The frequency shift is evaluated by the electronics and indicates the speed of the vehicle ahead Here is an example showing the effect of the Doppler shift: As the fire engine approaches, the observer hears a horn signal which has a more or less constant high pitch (high frequency) As the vehicle moves further away, the observer hears a lower pitched tone (transition to lower frequency) Pitch 620_010 Example showing how the speed and distance of the vehicle ahead are determined The vehicle ahead is driving faster and the vehicle-to-vehicle distance is increasing The frequency of the signal received (reflected) decreases (D fD) due to the Doppler shift and is timeshifted on the basis of time elapsed between signals transmitted and received This results in various differences in frequency between the rising (D f1) signal edge and the falling signal edge (D f2) This differential is evaluated by the control unit Frequency D fD f1 Relative velocity D f1 f2 f4 D f2 f3 620_011 Signal transmitted Signal received/reflected Determining the position of the vehicle ahead The radar signal propagates in a conical fashion Signal strength (amplitude) decreases with increasing distance from the transmitter in the vehicle's longitudinal axis (x) and transverse axis (y) y x Signal strength x, y 620_012 To determine the position, the angle at which the vehicle ahead is moving relative to one's self must be known Transceiver units equipped with four transmittes/receivers are used in current Audi models to generate this information The position of the vehicle ahead can be determined exactly by utilising the dependence of signal strength on the distance from the transmitter in combination with the four radar beams The radar beams overlap one another on the periphery In the diagram, the vehicle ahead is detected simultaneously by radar beams and If the vehicle in this example is to a greater extent located within the range of signal 2, the signal strengths (amplitudes) of signal received (reflected) will be greater than those of signal received The relationship between the strengths (amplitudes) of the signals received from each of the radar beams indicates the angle 620_013 10 Phase 4 If the driver still fails to take action and a collision at a high residual speed can no longer be avoided, the brake pressure will again be increased to the maximum rate of deceleration shortly before the calculated point of impact Audi pre sense additionally activates the belt tensioners The collision can no longer be prevented by the driver but the collision speed can be reduced by up to about 12 kph by applying maximum braking power Even if the driver takes no evasive action, Audi braking guard can reduce the impact speed by up to 40 kph The accident cannot be prevented without intervention by the driver, but its severity is significantly reduced by Audi braking guard • Emergency braking • Seat belt pretensioner activation 620_045 Unlike the ACC basic function, Audi braking guard also reacts to stationary targets In these cases, the driver is alerted by audible and visual warnings and, if necessary, by a warning jerk as described However, automatic braking is not performed at speeds above 30 kph Depending on model, the "full deceleration at low speeds" function is activated at speeds below 30 kph (see overview on page 25) Audi braking guard can be deactivated by the driver as a complete system Alternatively, it is possible to deactivate only the distance and collision warning functions Raise Handbook Driver assist When ESC sport mode or offroad mode is activated, Audi braking guard is also deactivated Audi braking guard System On Pre-warning On Car systems Set individual 620_046 In the Audi A3 from model year 2013 and later, the Audi braking guard functions are included in the functional range of Audi pre sense This concept will in future be implemented in all Audi models As with Audi braking guard, it is possible to deactivate Audi pre sense as a complete system or to deactivate the distance and collision warning functions only Car Handbook Audi pre sense System Pre-warning The Audi pre sense functions are partially deactivated when ESC sport mode is activated (or the Offroad mode in later Q models) CAR systems 620_047 30 Evolution The Audi braking guard function has grown in complexity over the course of its evolution The following chapter shows the developmental phases and functions of Audi braking guard in chronological order Audi braking guard Installed in A6 from MY 2005 − Pre-charging of the brake system by ESC in the event of a collision hazard − without warning the driver − Reduction of intervention threshold of Hydraulic Brake Assist (HBA) 2005 Audi braking guard with pre sense front/plus Installed in A8 from MY 2010 A6 and A7 from MY 2011 − Pre-charging of the brake system by ESC in the event of a collision hazard − Distance warning by warning lamp − Audible and visual collision warnings − Acute warning by brake jerk − Automatic partial braking if driver ignores warnings − Automatic emergency braking shortly before collision (only if vehicle is equipped with pre sense rear) − Reduced intervention threshold of Hydraulic Brake Assist (HBA) 2010 2007 Audi braking guard Installed in Q7 and A5 from MY 2007 A4 and Q5 from MY 2008 − Pre-charging of the brake system by ESC in the event of a collision hazard − Distance warning by warning lamp − Audible and visual collision warnings − Acute warning by brake jerk − Reduced intervention threshold of Hydraulic Brake Assist (HBA) 2013 2012 Model year Audi braking guard with pre sense and maximum deceleration at low speeds Installed in A4, A5, A6, A7 and A8 (phased in from MY 2012) A3 and Q5 from MY 2013 and later − Functions such as Audi braking guard with pre sense front/ plus − Automatic emergency braking at speeds of less than 30 kph 31 Audi Stop and go In the current Audi A3, S3, A6, S6, RS6, A7, S7, RS7, A8 and S8 models, the Stop and go function is implemented on vehicles equipped with ACC As previously with ACC in the Q7, the above vehicles also brake to a stop automatically A precondition for this is that the vehicle ahead was moving before it came to a stop Targets that are stationary at the point of detection are not included in the control function (e.g parked vehicles) If ACC registers that the vehicle ahead has come to a stop, the ACC-equipped vehicle is also automatically braked to a stop without any action on the part of the driver The rate of deceleration is dependent on the vehicle speed At vehicle speeds of less than 50 kph, the maximum rate of deceleration is approximately m/s2 The last 2-3 m before the vehicle comes to a stop are covered by "crawling" at a speed of approximately kph The stopping distance to the vehicle ahead is approximately 3.5 - m If the vehicle ahead starts off again after stopping briefly, the ACC-equipped vehicle will also accelerate and follow The braking operations necessary to implement this function are performed by the "brake pressure build-up" function of the ESC 620_049 The duration of start-off readiness is model-dependent and can be extended by a set amount using the stalk (RESUME position) 620_023b If ACC has brought the vehicle to a stop by an active braking operation, the electrical parking brake is automatically activated and ACC is deactivated in the following situations: • The vehicle is stationary for longer than • Opening the driver's door • System fault • In the case of the Audi A3 and S3 models, ACC is deactivated if the driver's seat belt is unfastened while the vehicle is stationary In the case of the Audi A6, S6, RS6, A7, S7, RS7, A8 and S8 models, the vehicle will no longer start off automatically 620_050 ! 32 Information In certain markets (e.g., USA) ), the vehicle executes a "stop" but does not automatically "go" To move off again, the driver must activate ACC with the stalk (RESUME) or by depressing the accelerator ACC-equipped vehicle starts off automatically Preceding vehicle starts off again Driver operates stalk ACC-equipped vehicle brakes to standstill Preceding vehicle stops Preceding vehicle Stationary Moving ACC-equipped vehicle Stationary Moving State ACC ready Not ready State Vehicles ACC system Max duration 15 s Operation Displays RESUME Operated Not operated Text ACC: ready No display ACC symbol Shown Not shown Example showing the time sequence of the control operations of an Audi A8 in Stop and go mode Time t 620_051 ACC READY is indicated to the driver in the central display The precondition for starting off is that the driver has fastened his seat belt In certain markets, the automatic start-off function is realised without the described option of extending the READY period with the stalk Distance - dynamic ACC: rreadyready 620_038 33 Start-off monitoring in Audi A6, S6, RS6, A7, S7, RS7, A8 and S8 Before the ACC-equipped vehicle starts off automatically, the ACC scans the area between the ACC-equipped vehicle and the vehicle ahead Audible and visual warnings are given if an obstacle is detected The vehicle nevertheless commences the drive-away cycle, but starts off but very slowly This gives the driver sufficient time to respond by braking or taking evasive action The area in front of the vehicle is monitored by three independent systems: the radar sensors, video camera R242 and the ultrasonic sensors of the parking aid If the vehicle is equipped with ACC, the ultrasonic sensors are operated in a different mode so that objects are still detected at a distance of approximately m If the signal from the video camera or the ultrasonic sensors is unavailable, the vehicle will always start off automatically at a reduced rate of acceleration Automatic start-off is suppressed if both signals are unavailable The system is then deactivated and the driver is requested to take over 620_053 In the Audi A3 and S3, drive-away readiness is limited by "RESUME" to s (in the Audi A6, S6, RS6, A7, S7, RS7, A8 and S8, this is 15 s) Because this duration is so short, the Audi A3 and S3 models not have a special start-off monitoring function Hill Start Assist in combination with Audi Stop and go Stop and go can also be combined with Hill Start Assist The drive assist function can be activated/deactivated independently of the ACC at any time If Hill Start Assist and Audi Stop and go are active while the vehicle is stationary, the Hill Start assist function will switch passively into the background (comparable to "standby" mode) If ACC is switched off while the vehicle is stationary and Hill Start Assist is on, Hill Start Assist is re-activated and holds the vehicle stationary 620_054 ! 34 Information Automatic restarting can be deactivated using the diagnostic tester Full deceleration at low speeds Overtaking assistance This function was first introduced in the Audi A4, A7 and A8 models from model year 2012 The vehicle is braked automatically when a risk of collision exists at low vehicle speeds under 30 kph The data collected by the ACC is the basis for detection of the collision risk In the case of the A6, S6, RS6, A7, S7, RS7, A8 and S8 models, the video information from camera R242 is factored in when evaluating the hazard potential This assessment is made by specific software on the ACC control unit The control unit then "instructs" the ESC control unit to brake the vehicle by indicating a nominal rate of deceleration (approximately -8 m/s2) The ESC control unit then initiates the build-up of brake pressure at all four wheel brakes This function facilitates rapid overtaking manoeuvres When a turn signal is activated, the ACC interprets that the driver wishes to overtake The vehicle is then accelerated before leaving its lane and until the overtaking maneouvre is complete This is essentially how a driver would behave during "normal" driving The function is activated in a situation-dependent way 620_055 620_056 Cornerning assistance Control behaviour when cornering ACC utilises the predictive route data of the navigation system to perform this function If a corner is detected in the road ahead, ACC computes the speed at which this corner can be safely taken Cornering assist will be activated if the vehicle's current speed exceeds the nominal speed computed by ACC The vehicle's speed is reduced by up to 10-15 kph on entering the corner by reducing the drive torque (utilisation of engine drag torque) If ACC detects that a vehicle's transverse acceleration exceeds a calculated nominal value, the vehicle's speed is reduced accordingly In this example, the set target speed is 120 kph and the vehicle takes a corner with a clear road ahead, i.e the vehicle does not have to maintain a target distance to a slower-moving vehicle ahead While the vehicle is rounding the corner, the ACC control unit computes a nominal speed of 110 kph based on the measured transverse acceleration The vehicle's speed is then limited to110 kph by reducing the drive torque Allowance if made for trailer operation and the selected driving program when determining the nominal speed 620_057 620_052 35 Overtaking prevention in right driving lane If ACC mode is active and the road ahead is clear, overtaking/ passing in the right driving lane is only possible without restrictions up to a defined vehicle speed It is only possible to pass a vehicle at a limited relative speed of approx 10 kph The function is now active and does not allow overtaking/passing in the right lane The active function can be cancelled at any time by accelerating manually with the stalk (RESUME), by depressing the accelerator pedal or by increasing the set speed Driving speed V2 V1 620_058 Unrestricted overtaking on the right (up to speed V1) Overtaking on the right is only possible at a limited relative speed (up to speed V2) Overtaking on the right is not possible (at speed V2 or higher) 620_059 36 Lane change assistance To realise this function, the vehicle must be equipped with Audi side assist and camera R242 Braking intervention is adapted to the following traffic and the oncoming traffic in the overtaking lane The camera detects the lane markings Two typical driving situations will now be used to explain how ACC works 620_060 Driving situation The ACC-equipped vehicle is rapidly approaching a slower-moving vehicle ahead and the driver operates the turn signal to indicate that he wishes to change lane The rear radar sensor indicates to Audi side assist that the left lane behind the vehicle is clear Also, ACC detects no vehicle in the left lane ahead of the ACC-equipped vehicle The camera identifies the broken lane markings ACC derives the following information from the input signals: • It is safe to overtake because there is no subsequent traffic in the left lane • The lane change can be performed without reducing speed because there is no other vehicle ahead in the overtaking lane • Broken lane markings mean overtaking is permitted There is a high likelihood that the driver will perform the overtaking manoeuvre When the set target distance is achieved, ACC does not brake the vehicle to the speed which it would otherwise set when following a vehicle in front without performing an overtaking manoeuvre This means that the lane change can be performed much more smoothly and comfortably 37 Driving situation The ACC-equipped vehicle is rapidly approaching a slower-moving vehicle ahead and the driver operates the turn signals to indicate that he wishes to change lane The rear radar sensor indicates to Audi side assist that the left lane behind the vehicle is busy ACC also detects a vehicle in the left lane ahead of the ACC-equipped vehicle The camera identifies the broken lane markings ACC derives the following information from the input signals: • It is only to a limited degree safe to overtake because there is subsequent traffic in the left lane • The lane change cannot be performed without reducing speed because there is another vehicle ahead in the overtaking lane • Broken lane markings mean overtaking is permitted There is a high likelihood that the driver will perform the overtaking manoeuvre When the set target distance is achieved, ACC brakes the vehicle to a lower speed than in the above example The speeds of the vehicles driving in the left lane are taken into account when determining the required amount of corrective braking 620_061 If the camera detects solid lane markings, a lane change is assessed as improbable and the braking interventions are executed as they would be when driving in lane without changing lane Boost function The boost function enables the driver to increase the driving speed currently set by ACC without having to deactivate ACC This is achieved by depressing the accelerator pedal or by pulling the stalk If the boost function is no longer required, ACC slows down again to the originally set speed 620_063 38 Service operations The most common service operations are briefly explained in this chapter The ACC systems (ADR sender, right G259 and ACC control unit J428/left adaptive cruise control sender G258 and ACC control unit J850) have full self-diagnostic capability Detected events are stored in the vehicle's event memory at diagnosis address 13 / 8B together with details of the ambient conditions in each case Corresponding fault finding programs are linked to the entries in the event memory Sensor vision Despite the "robust" propagation characteristics of the radar beam, ACC may be deactivated due to impaired conditions of "visibility" This can happen for various reasons • The propagation of the radar beam is significantly impaired by the weather conditions This is possible in spray, fog and snow This can only be remedied by an improvement in the weather conditions ACC and Audi braking guard: currently unavailable No sensor vision • The lens on the radar sensor is dirty After the lens has been cleaned, ACC will again be available Commercially available cleaning agents can generally be used for cleaning all motor vehicles • The vehicle is operated in a region where very few objects are definable by the ACC as targets This is rarely the case, e.g when driving through desert-like regions 620_064 • When passing through tunnels, signal reflection off the tunnel walls may lead to deactivation of the ACC Replacement and removal/installation of the ACC sender with ACC control unit In the event of a fault in the sender or control unit, the complete ACC unit must always be replaced It is not permitted to separate both components It is necessary to calibrate the sender after installing the ACC unit 620_025 ! Information It is important that basic setting of the stud length be correctly performed prior to installation of the ACC unit Refer to the workshop manual for detailed information 39 Calibrating the ACC sender To ensure precise operation, the sender(s) must be exactly calibrated Only then can a vehicle driving ahead in the same lane be identified as a relevant vehicle If the sender is not set precisely in the horizontal direction, the system may incorrectly react to vehicles driving in the adjacent lanes 620_066 The bumpers of the Audi A8 have been replaced The senders have been installed without subsequently being calibrated By incorrectly aligning with the left lane, ACC now controls the distance to the passenger car driving in this lane and not the truck in the same lane This unwanted control behaviour is even more noticeable when cornerning, particularly in the left hand corners in this example The sender must be calibrated if: In vehicles equipped with two ACC units (ADR sender, right G259 and ACC control unit J428 as well as left adaptive cruise control sender G258 and ACC control unit J850), both senders must always be set The setting procedure should begin with sender G259, which acts as the master • the rear axle tracking has been adjusted • the ACC unit (sender and control unit) have been removed and installed • the front bumper has been removed and installed • the front bumper has been loosened or displaced • the front bumper has been damaged by the application of excessive force to the bumper • the horizontal misalignment angle is outside the range -0.8° to +0.8° ADR sender, right G259 and ACC control unit J428 (master) Left adaptive cruise control sender G258 and ACC control unit J850 (slave) 620_027a 40 The ACC unit is attached to the baseplate by three studs The baseplate is rigidly bolted to the bumper The studs are tipped with ball heads The ball heads are mounted in plastic ball joint sockets fitted into mounting eyelets in the baseplate The screw threads are inserted in plastic elements on the sender (clips) Two of the three screws (A,B) are for setting the sender; the third screw (C) is non-adjustably attached to the sender housing Turning the screws (A or B) adjusts the distance between the sender and the baseplate The sender is pivoted about the axis formed by the non-adjustable screw (C) and by the second, adjustable screw (B or A) This allows the senders to be adjusted independently in the horizontal direction (red axis) and in the vertical direction (blue axis) This adjustment (turning of the screws) can be made using the setting tool VAS 6190/2 620_068 = plastic ball joint sockets = mounting bracket = cover = stud = clip = ACC sender and ACC control unit 620_067 A prerequisite for successful calibration of the ACC sender is that the stud length is correctly set 620_065 41 A sender can be calibrated using the following special tools: • VAS 6190A (not suitable for A6, S6, RS6, A7, S7, RS7, A8 and S8, no longer included in workshop equipment range) • ACC setting device VAS 6430 or setting device, basic set VAS 6430/1 together with ACC reflector mirror VAS 6430/3 620_069 The basic principle of the calibration procedure is the same irrespective of ACC system and vehicle model: A mirror is positioned in front of the vehicle at right angles to the vehicle's geometric driving axis (the geometric driving axis indicates the running direction of the rear axle and, thus, the vehicle's direction of motion when driving in a straight line) Exact positioning of the mirror necessitates the use of an axle alignment stand and initial alignment of the vehicle To determine whether the position of the radar sensor is within the nominal range, a full vehicle alignment procedure must be performed A "quick-entry" wheel alignment procedure is sufficient (performance of rim runout compensation together with alignment of the rear axle track width) ! The radar sensors are then instructed by the ACC control unit to transmit radar waves and receive the waves reflected by the mirror The mechanic initiates this procedure using the diagnostic tester The sender is set correctly if the reflected radar waves impinge on the ACC control unit in exactly the same position from which they originated The control unit evaluates the extent of the deviation from the point of origin and thereby determines the misalignment angle The diagnostic tester tells the mechanic what adjustment to make at the relevant setting screw Information A key requirement for an exact adjustment is the careful alignment of the mirror perpendicular to the geometric driving axis If this setting is not made correctly, the remainder of the setting procedure will go smoothly but the sender will still exhibit too large a misalignment angle after the calibration has been completed 620_070 42 ACC transmits and receives signals after it is initialised following engine start-up The ACC system permanently transmits and receives signals during the subsequent driving cycle (after terminal 15 "on") even if the driver has not activated the system Even during subsequent stop cycles in vehicles equipped with the Start Stop System, ACC continues to transmit and receive signals The system detects a misalignment of the sender by evaluating the following key information: Forces acting directly on the peripheral regions of the ACC unit may be sufficient to force the ball head tips of the studs out of the ball joint sockets in the mounting bracket This can, for example, occur in the winter if the bumper is driven into a snow bank when parking the vehicle In these cases, the misalignment angle will be sufficiently large to initiate system deactivation In most cases, subsequent calibration efforts will prove unsuccessful This is why it is important to always check that the sender is properly attached before it is calibrated • objects detected by ACC (crash barriers, other vehicles) • yaw rate (vehicle movement about the vehicle's vertical axis) The measured value for horizontal misalignment angle, which can be read out using the diagnostic tester, is important information that allows service centres to assess the system's behaviour Even deviations in the order of approximately 0.8° are very noticeable in the control behaviour of the system and should be corrected by calibrating the sender at a qualified service centre If the deviation exceeds approximately 1.4°, the system will be shut down and an entry will be made in the vehicle's event memory l The misalignment angle of ACC control unit (J428) is currently 0.048° l The misalignment angle of ACC control unit (J850) is currently 0.26° Calibration is not necessary until a misalignment angle of 0.8° is exceeded Should ACC control units (J428 and J850) still be re-calibrated? Help Cancel test 620_071 43 All rights reserved Technical specifications are subject to change Copyright AUDI AG I/VK-35 service.training@audi.de AUDI AG D-85045 Ingolstadt Technical status 11/13 Printed in Germany A13.5S01.04.20 620 Audi Vorsprung durch Technik ... possible to activate ACC while shifting gear The ACC systems used on Audi vehicles are joint developments of AUDI AG and Robert Bosch AG *: including S models and RS models Model A3, S3 ACC version **... limit the performance of the ACC system 12 Description of ACC system ACC options The following overview shows the current Audi models (model year 2013) in which ACC is optionally available A... activated, Audi braking guard is also deactivated Audi braking guard System On Pre-warning On Car systems Set individual 620_046 In the Audi A3 from model year 2013 and later, the Audi braking