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Home >> Audi >> 2002 >> S4 Quattro, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics - 2.7L Turbo >> Data Transfer Between Engine Control Module And Can-Bus Capable Control Modules
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Data Transfer Between Engine Control Module And Can-Bus Capable Control Modules

Data is transferred between control modules through the CAN-bus (Databus) system. CAN-bus refers to a network connecting various control modules. Data is transferred between modules serially (one module after the other), through CAN-bus network. If DTC testing suggests checking data exchange between ECM and CAN capable control modules perform following procedure:

  1. Connect VAS 5051 or equivalent scan tool to DLC. DLC is located behind cover under left side of steering column. See Figure. Start engine. On scan tool press "01" to select address word 01- ENGINE ELECTRONICS. Press "Q" button to confirm input. Press "08" to select diagnostic function 08 - READ MEASURING VALUE BLOCK. On scan tool, enter 125 to select DISPLAY GROUP 125. Press "Q" button to confirm input. Go to next step.
    2. NOTE: Measuring value blocks 125 and 126 read in diagnostic function 08 - READ MEASURING VALVE BLOCK indicate control modules connected to powertrain databus.
  2. CAN-bus capable control modules in display group 125, are displayed in display fields 1-4. NO INDICATION: indicates control module is not CAN-bus capable. INDICATION 1: indicates CAN-bus capable control module is connected to databus. INDICATION 0: indicates CAN-bus capable control module is not connected to databus. On scan tool, press "S" button to switch to display group 126. Check display group 126 for CAN-bus capable modules. On scan tool, press 08 - ERASE DTC MEMORY. Press "06" to select diagnostic function 06 - END OUTPUT, and go to next step.
  3. Press "00" to select diagnostic function 00 - CHECK DTC MEMORY - COMPLETE SYSTEM. DTC memory of all OBD capable systems in the vehicle will be checked. When each control module responds with it's identification, scan tool display indicates number of stored DTCs, or NO MALFUNCTIONS RECOGNIZED. DTC stored in memory are indicated in sequence and printed out. VAG scan tool sends next address word. Go to next step.
  4. If malfunction related to powertrain databus or CAN-bus is indicated. Check that ECM or other CAN-bus capable control modules installed are appropriate for vehicle (check part number and coding). Check for poor or loose terminals in control module harness connectors. If problem is found, repair as necessary. If no problem is found, go to next step.
  5. Using stored DTCs and data link connectors wiring diagram, analyze which control modules are not communicating. Use example in illustrations to determine non-communicating modules. See Fig 1-Fig 3 . Turn ignition off. Disconnect CAN-bus connected control module harness connectors. In examples 1 and 2, check for open circuits in bus wires of connected control modules. In example 3, check for short to voltage in circuits in bus wires of connected control modules. If problem is found, repair as necessary. If no problem is found, replace suspect control module. Go to next step.
    Fig 1: Example 1: Locating Non-Communicating Control Module
    G00077136Courtesy of AUDI OF AMERICA, INC.
    Fig 2: Example 2: Locating Non-Communicating Control Module
    G00077140Courtesy of AUDI OF AMERICA, INC.
    Fig 3: Example 3: Locating Non-Communicating Control Module
    G00077144Courtesy of AUDI OF AMERICA, INC.
  6. If cause for Powertrain CAN-bus malfunction DTC can not be determined, check if DTC was caused by one of the control modules. Turn ignition off. Disconnect all control modules on CAN-bus circuit.
    • Connect one of the control modules.
    • Connect VAG 5051 scan tool. Turn ignition on. Using scan tool erase DTC memory of last connected control module. End scan tool output using function 06 - END OUTPUT.
    • Turn ignition on and off.
    • Leave ignition on for 10 seconds or more. Using scan tool read DTC memory of last connected control module.
    • If scan tool displays, POWERTRAIN CAN-BUS MALFUNCTION, replace last connected control module.
    • If scan tool does not display, POWERTRAIN CAN-BUS MALFUNCTION, connect next control module and repeat procedure.
  7. Continue repeating procedure until malfunctioning module is determined. Using scan tool, clear DTCs. Test drive vehicle. Using scan tool, retrieve DTCs. If DTC does not reset, testing is complete.

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