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The Tire Pressure Monitoring System

The tire pressure monitoring system used by Audi is a four-wheel system. Although the spare wheel is monitored and “managed” by the Tire Pressure Monitoring Control Module J502, it is excluded from the system status messages. (For further details, refer to Spare Wheel.) Data transfer from the sensors at each wheel to the Tire Pressure Monitoring Control Module J502 is by radio-frequency (RF) transmission. Information exchange between the peripheral components in the vehicle takes place via the convenience CAN data bus. A measuring and transmitter module mounted on the tire valve sends a radio signal at regular time intervals to the antenna for tire pressure monitoring integrated in the wheel housing. This signal is then relayed to the Tire Pressure Monitoring Control Module J502. The Tire Pressure Monitoring Control Module J502 evaluates the tire pressures and any pressure changes and sends corresponding system status messages to the Instrument Cluster Combination Processor J218. These messages are indicated to the driver on the display of the Driver Information System (DIS). The tire pressure monitoring system offers the following advantages:

  • Increased safety through early “low tire pressure” warnings.
  • More convenience through the elimination of regular tire pressure monitoring. The tire pressure need only be corrected when this is indicated.
  • Longer service life of tires. A pressure deficit of 4.4 psi (30 kPa) can reduce the service life of tires by up to 25%.
  • Lower fuel consumption through correct tire pressure.
  • Tire pressure monitoring differentiates between the following situations:

  • Slow loss of pressure.
  • Sudden loss of pressure.
  • Flat tire when the vehicle is stationary.
  • A slow loss of pressure is indicated to the driver at an early stage so the driver can check the tires or correct the tire pressure. If a sudden loss of pressure occurs (blowout, flat tire) while travelling, the driver is alerted immediately. The driver will normally notice this anyway by the way the vehicle reacts. The tire pressure monitoring system indicates the loss of pressure to the driver at an early stage so that he or she can take appropriate action. The system indicates a flat tire when the vehicle is stationary to the driver directly after turning on the ignition.

    System Components
    Vehicle Overview

    The tire pressure monitoring system includes the following components:

  • Five tire pressure sensors
  • Four Antennas for Tire Pressure Check
  • Tire Pressure Monitoring Control
    Module J502
  • Instrument Cluster Combination
    Processor J218
  • Function Selector Switch II E272
  •  

    Metal Tire Inflation Valves

    The tire inflation valves have been redesigned for use with the tire pressure monitoring system. Metal valves are now used in place of the rubber valves used previously. Metal valve bodies are reusable. When installing a new tire on a used rim, only the valve insert need be replaced .

    Sensors for Tire Pressure:
    Front Left G222
    Front Right G223
    Rear Left G224
    Rear Right G225
    Spare Tire G226

    The Sensors for Tire Pressure are attached to the metal tire inflation valves by screws and can be reused after replacing the tires or wheels. The following components are integrated in each Sensor for Tire Pressure:

  • Transmitter antenna.
  • Pressure sensor.
  • Temperature sensor.
  • Measuring and control electronics.
  • Battery.
  • The pressure sensor, temperature sensor, and measuring and control electronics integrated into each, result in an intelligent sensor. The pressure sensor records the momentary tire pressure (absolute pressure measurement) and sends the measured data to the Tire Pressure Monitoring Control Module J502 for evaluation purposes. The temperature sensor has two functions:

  • To compensate for the temperaturedependent
    changes in tire pressure.
  • For diagnostic purposes.
  • If a defined temperature threshold is exceeded, the temperature sensor stops radio transmission. (For further details, refer to Temperature Cut-Out.) Temperature compensation is controlled by the Tire Pressure Monitoring Control Module J502. The measured tire pressures are normalized to a temperature of 68°F (20°C).

    Depending upon the vehicle marketing area, two different carrier frequencies are used for radio transmission:

  • The carrier frequency of 433 MHz is permitted in most countries.
  • A 315 MHz carrier frequency is used in the United States and Canada and in a few other countries
  • The carrier frequency is printed on the sensors, antennas and control units. It can also be identified by the part number. The tire pressure monitoring system only works with system components with the same carrier frequency. The air pressure in a closed system changes in proportion to temperature. In normal circumstances, a temperature change of 18°F (10°C) results in a pressure change of 1.45 psi (10 kPa).

    Explanatory notes:

    Atmospheric pressure is the term used to describe the air pressure at the earth’s surface. At mean sea level, this pressure averages about 14.7 psi (101.3 kPa), also commonly referred to as 1 atmosphere or 1 bar for practical applications (more precisely, 1 bar is equivalent to 0.98697 atmosphere, or 14.51 psi (100kPa)).

    Relative pressure indicates a pressure using atmospheric pressure as the starting point.

    Absolute pressure is the pressure using zero pressure as the starting point.

    The transmitter antenna of each Sensor for Tire Pressure sends the following information:

  • Individual ID number (ID code).
  • Momentary tire pressure
    (absolute pressure).
  • Momentary tire air temperature.
  • Condition of integrated battery.
  • Status, synchronization, and
    control information required for safe
    data transfer.

    This information is contained in a data
    message 12 bytes in length. The data
    transfer is frequency-modulated and the
    transfer time is approximately 10 ms.

    Temperature cut-out

    In order to avoid generating erroneous information, no further radio signals (data messages) are sent when the Sensor for Tire Pressure registers a temperature of approximately 248°F (120°C). Shortly before the Sensor for Tire Pressure turns off the transmitting electronics, the Tire Pressure Monitoring Control Module J502 is informed that a “temperature cutout” is imminent. A fault message to this effect is then stored in the fault memory. If the temperature drops below a defined limit, the sensor will again enter radio mode. If a temperature cut-out is activated for one or more sensors, the yellow message symbol appears.

    The power supply to the Sensors for Tire Pressure

    The measuring, control and transmitting electronics in the Sensors for Tire Pressure receive their power supply from an integrated lithium battery. To prolong the service life of the Sensors for Tire Pressure for as long as possible, the control electronics include an ingenious “energy management system.”

    The energy management system

    Relatively few measured-data transmissions are needed for the tire pressure measurements. However, a loss of pressure must be detected immediately and indicated to the Tire Pressure Monitoring Control Module J502. The energy management system can differentiate between the normal transfer mode and the high-speed transfer mode, because there are differing measuring and transfer intervals for each mode. When the tire pressure readings are constant, the Sensors for Tire Pressure are in normal transfer mode. If a loss of pressure of more than 2.9 psi (20 kPa) per minute occurs, the Sensor for Tire Pressure immediately is switched to a high-speed transfer mode. In this way, the energy management system keeps the load on the sensor battery as small as possible and ensures high-reliability monitoring at the same time. A theoretical battery service life of up to 7 years is therefore possible.

    Antennas for Tire Pressure Check:
    Front Left R59
    Front Right R60
    Rear Left R61
    Rear Right R62

    The Antennas for Tire Pressure Check receive the radio signals from the Sensors for Tire Pressure and transfer them to the Tire Pressure Monitoring Control Module J502 for further processing. The tire pressure monitoring system uses four Antennas for Tire Pressure Check which are installed in the wheel housings at the front left, front right, rear left and rear right behind the wheel housing liners. They are connected to the Tire Pressure Monitoring Control Module J502 by shielded high-frequency antenna wires in accordance with their installed locations. The antennas receive all the radio signals within their reception range and frequency band. Each antenna receives the radio signals from all the Sensors for Tire Pressure located in its range. The radio signals are filtered and selected in the Tire Pressure Monitoring Control Module J502 to ensure that the correct data are processed.

    Self-diagnosis

    The Antennas for Tire Pressure Check are currently not monitored by the selfdiagnosis. If “no signal” is recorded in the fault memory for a Sensor for Tire Pressure, either the antenna or the antenna wiring for that sensor may be affected. A provision has been made for antenna diagnosis at a later date. You will find information regarding this in the relevant Repair Manual when it becomes available.

    Tire Pressure Monitoring Control Module J502

    The Tire Pressure Monitoring Control Module J502 evaluates the radio signals from the Antennas for Tire Pressure Check, prioritizes these signals and transfers the relevant information to the instrument cluster. Where corresponding relevant warnings are issued by the driver information system (DIS) display.

    Communication with the peripheral tire pressure monitoring components in the vehicle takes place via the convenience CAN data bus. The system status messages are prioritized by evaluating different limit values, as well as the pressure drop, as a function of time (the pressure drop gradient).

    For this purpose, two independently stored tire pressures are saved to the Tire Pressure Monitoring Control Module J502: The first of these are the encoded tire pressures for the partly loaded condition and the fully loaded condition programmed into the Tire Pressure Monitoring Control Module J502 (refer to Repair Manual for more information about encoding the module). These pressures refer to the data on the sticker affixed to the fuel filler door and are entered with the help of the coding table. A lower pressure limit is calculated using the pressure for the “partly loaded (condition)” as the starting point (refer to description of system messages). The second tire pressure stored is set by the driver using the menu item “Save pressures!” on the Driver Information System (DIS) display (refer to the vehicle Owner’s Manual). Using the DIS menu, the driver can store his individual tire pressures (e.g. for fully loaded condition or winter tires).

    System Functions

     

    Operation

    The tire pressure monitoring system can be turned off and on with the Function Selector Switch II E272. The current tire pressures can be stored in the “Tire pressure” submenu.

    Storing the tire pressures

    Check, correct, and store the tire pressures when the tires are cold to avoid inaccurate settings. Check and correct the inflation of all the tires on the vehicle at the same time using the same tire gauge and air supply. Execute the “Save pressures!” function from the DIS menu after checking or correcting the tire pressures to avoid generating faulty signals. Ignoring these precautions and monitoring or correcting the tire pressures of different tires using a different air supply or tire gauge will lead to premature or delayed system status messages depending upon the differences in the temperature and quality of the air supply and the tolerances of the tire gauges. This also applies if the tire pressures are corrected when their temperatures are different (such as when including the spare in the tire rotation sequence), or if some tire pressures are corrected at different ambient temperatures than others (some in summer and others in winter), and the pressures are not stored each time pressure corrections are made. The desired menu option can be selected with the rotary switch/pushbutton of the Function Selector Switch II E272 (refer to operating instructions).

    Turning the system off and on

    The system can be turned off and on by the driver using the DIS menu. The yellow status message symbol for “tire pressure monitoring system off” is displayed briefly whenever the ignition is turned on and the system is off.

    Status Messages

    System status messages are divided into two priority levels depending on their effect on vehicle handling and performance. Priority 1 messages have high significance and are intended for system states in which driving safety is no longer assured. Priority 1 status messages are indicated by red warning symbols on the DIS display and by acoustic chime signals. The driver is asked to check the condition of the tires immediately. Priority 2 messages have low significance and are intended for system states which are non-critical with regard to driving safety. The driver is informed about the condition of the system by yellow symbols on the DIS display. As a rule, priority 1 and 2 status messages are each further subdivided into two categories: “no position” and “position-related.” “No position” means that the system cannot give exact information regarding the fault location, or that there are several fault locations which lead to the status message “no position.” “Position-related” means that the system can determine the fault location exactly and only this location can be responsible for causing the fault

    Priority 1 Messages are displayed under the following conditions:

  • The actual tire pressure drops below
    alarm threshold 2.
  • The actual tire pressure drops below
    alarm threshold 3.
  • The pressure loss gradient is greater than
    0.2 bar per minute (2.9 psi per minute
    (20 kPa per minute)).
  •  

    Priority 2 messages displayed when the actual tire pressure drops below alarm threshold 1

    These messages are displayed when the actual tire pressure in a wheel is 0.2 bar (2.9 psi (20 kPa)) less than the specified tire pressure stored using the DIS menu (alarm threshold 1). At the same time, the Tire Pressure Monitoring Control Module J502 must know the positions of the Sensors for Tire Pressure (priority 2, position-related). In addition, a difference of more than 0.1 bar (1.45 psi (10 kPa)) between actual tire pressure and the stored specified tire pressure must not be received from any of the other three Sensors for Tire Pressure. If a wheel reaches alarm threshold 1 and if one or more of the other wheels is 0.1 bar (1.45 psi (10 kPa)) below the stored specified tire pressure, the DIS displays the yellow status message symbol and all four positions. No single position is isolated as the location of the fault. In this way, the driver is prompted to check the tire pressures of all the wheels and correct them as needed. This ensures optimum tire pressure maintenance and reduces the number of system alarms.

    Further conditions relating to actual tire pressure drops below alarm threshold 1

    The temperature value transferred by the Sensors for Tire Pressure must not be more than 27°F (15 °C) above the ambient temperature when the ignition is turned on. If this temperature threshold is exceeded, the alarm message is suppressed. The alarm messages concerning actual tire pressure drops below alarm threshold 1 are not displayed until the ignition is turned on again. The alarm messages concerning actual tire pressure drops below alarm threshold 1 are cancelled if:

  • a tire pressure which deviates from the
    stored specified tire pressure by less
    than 0.1 bar (1.45 psi (10 kPa)) is
    received from all Sensors for Tire
    Pressure, and
  • the pressures are stored again using the
    DIS menu.
  • Priority 2 messages displayed when the pressure differential between wheels on the same axle is greater than 0.4 bar (5.80 psi (40 kPa)) These messages are displayed when the pressure differential between the wheels on an axle (front axle, rear axle or on both axles) is greater than 0.4 bar (5.80 psi (40 kPa)). This can occur if tire pressure correction is not performed properly, such as if a wheel has been omitted from the checking and correction routine. If this happens, the driver must recheck and correct the tire pressures and repeat the “Save pressures!” function using the DIS menu.

    Further conditions relating to the pressure differential between wheels

    The temperature values determined by the Sensors for Tire Pressure must not be more than 54°F (30°C) above the ambient temperature. The alarm message is suppressed when this temperature threshold is exceeded. The alarm messages concerning the condition that the pressure differential between wheels on the same axle is greater than 0.4 bar (5.80 psi (40 kPa)) are cancelled if the pressures are stored again using the DIS menu.

    Priority 2 messages displayed when the system is turned off or unavailable due to faults

    The tire pressure monitoring system can be deactivated by the driver using the DIS menu. This is expedient when wheels with Sensors for Tire Pressure are transported in the luggage compartment or when wheels without Sensors for Tire Pressure are mounted (winter wheels with snow tires for example). This status message is displayed briefly as information for the driver whenever the ignition is turned on.

    If the system is not available due to radio frequency interference, these yellow status message symbols will appear on the DIS display. This can occur when the Antennas for Tire Pressure Check receive no data messages due to interference from electromagnetic fields. Possible interference factors include stray ignition shorts to ground (spark plug wire not installed correctly) or the use of infrared headphones. The message is cancelled when the radio frequency interference is no longer present and the data messages from the Sensors for Tire Pressure have been received. This message is only indicated at vehicle road speeds greater than 3.1 mph (5 km/h). This yellow status message symbol appears on the DIS display in the event of other system disturbances, indicating that the tire pressure monitoring system is not available. (See also “Temperature cut-out.”)

    Own Wheel Recognition

    Each of the Sensors for Tire Pressure has its own ID code in the form of a 10-digit number. The ID codes are included in the data messages from the Sensors for Tire Pressure and are transferred continuously to the Tire Pressure Monitoring Control Module J502. The Tire Pressure Monitoring Control Module J502 defines and stores the ID codes for the Sensors for Tire Pressure belonging to the vehicle under specific conditions. This process is referred to as “own wheel recognition.” Up to five Sensors for Tire Pressure can be managed by the system (including the Sensor for Tire Pressure, Spare Tire G226). The ID codes received are compared continuously with the ID codes stored in the memory, and only the data messages of the stored sensors are processed. This ensures that signals from non-system sensors located within radio reception range do not affect the system. The own wheel recognition system is an adaptive system. The Tire Pressure Monitoring Control Module J502 recognizes when wheels with different Sensors for Tire Pressure are mounted. The “new” Sensors for Tire Pressure are recognized and stored under specific conditions through algorithmic evaluation.

     

    Sensors for Tire Pressure are only adapted to the system while the vehicle is moving. This protects the system against interference from the tire pressure monitoring systems of other vehicles parked in the vicinity, for example. When the function “Save pressures!” is invoked from the DIS menu, the Tire Pressure Monitoring Control Module J502 is requested to repeat the own wheel recognition and position assignment processes in addition to storing the new tire pressures. Transporting wheels with Sensors for Tire Pressure inside the vehicle is a source of RF interference and may cause the system to generate erroneous information. The ID codes of the individual Sensors for Tire Pressure can be displayed under various display groups with the Vehicle Diagnosis, Test and Information System VAS 5051, using function 08 — Read measured value block.

    Position Recognition

    To be able to display position-related alarm messages to the driver, the Tire Pressure Monitoring Control Module J502 must know the locations of the Sensors for Tire Pressure on the vehicle. Position recognition is an additional function performed by the Tire Pressure Monitoring Control Module J502. It assigns the Sensors for Tire Pressure automatically and independently to the installed locations of the wheels on the vehicle at the front left, front right, rear left and rear right, as well as the spare wheel. This is made possible by the use of four receiver Antennas for Tire Pressure Check and evaluating the reception signals of varying strength from the individual Sensors for Tire Pressure. The Tire Pressure Monitoring Control Module J502 determines the theoretical positions of the Sensors for Tire Pressure (installed locations of the wheels at the front left, front right, rear left and rear right, as well as the spare wheel) using algorithmic calculations and statistics. Because of the many factors that can affect signal strength in radio transmission (e.g. shielding by metal parts, distance from transmitter to antenna, environmental influences etc.), the system cannot always determine the position of each Sensor for Tire Pressure with 100% certainty. Therefore, the term “theoretical position” is used.

    Monitoring function when the vehicle is stationary

    To ensure that the monitoring function also works when the vehicle is stationary, the Tire Pressure Monitoring Control Module J502 remains active after the ignition has been turned off. The Tire Pressure Monitoring Control Module J502 enters energy-saving mode. It self-activates at regular intervals shortly before the data messages are transmitted by the Sensors for Tire Pressure at each wheel. This function helps to preserve the vehicle battery charge and ensures that a flat tire is indicated on the DIS display before the vehicle is moved.

    Spare Wheel

    The spare wheel has a special status in the tire pressure monitoring system. It is equipped with a Sensor for Tire Pressure, Spare Tire G226. Unlike the other wheels, the tire pressure monitoring system does not have a separate Antenna for Tire Pressure Check for spare tire pressure monitoring. The Antennas for Tire Pressure Check at each of the four wheel housings receive the data message radio signals from the Sensor for Tire Pressure, Spare Tire G226, and send these signals to the Tire Pressure Monitoring Control Module J502. The own wheel and position recognition functions identify the “fifth wheel” as a spare wheel, and it is registered as such in the Tire Pressure Monitoring Control Module J502. Tires — Tire Pressure Monitoring The tire pressure in the spare wheel can be monitored using the Vehicle Diagnosis, Test and Information System VAS 5051, using Address Word 65, Function 08, Read measured value block, Display group 13. The prerequisite for this is that the position recognition process has been completed. This is the case when “015” is displayed under Display group 19. Although the Tire Pressure Monitoring Control Module J502 “manages” the spare wheel, system alarm messages pertaining to the spare wheel are suppressed and not indicated. A priority 1, “no position” status message may be caused by the spare wheel if the tire inflation pressure is below alarm threshold 3 and position recognition has not yet been performed by the system. This could occur after “Save pressures!” has been initiated using the DIS menu or after a wheel change, but before the vehicle has been driven long enough for the system to complete the own wheel recognition and position assignment processes. The message is cancelled once position recognition has been completed by the system and the spare wheel is recognized as such.

     

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    847-371-1937

    E-mail: service@dynarev.com

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    Mundelein, IL 60060

    Business Hours: Monday thru Friday 9:00 am - 5:00 pm CST

    Extended hours are available by appintment. (7am-10pm)


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