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Test B: Scan Tool Does Not Communicate With Class 2 Device

WARNING: This page is about a different car, the 2001 Cadillac Seville. However, it is still accessible from the selected car via links, so may be relevant.
  1. Connect scan tool to Data Link Connector (DLC). DLC is located below left side of instrument panel, near steering column. See Figure . If scan tool powers up, go to next step. If scan tool does not power up, perform TEST A: SCAN TOOL DOES NOT POWER UP  .
  2. Turn ignition switch to RUN position. Using scan tool, attempt to communicate with each module on class 2 serial data circuit. See CLASS 2 SERIAL DATA LINE  under DESCRIPTION & OPERATION. If scan tool communicates with any module, go to next step. If scan tool does not communicate with any module, go to step  8 .
  3. Using scan tool, select DISPLAY DTCs function for each module. Record all DTCs, status and module which stored DTC. If any DTCs within U1000 or U1305 are retrieved, go to next step. If any DTCs within U1000 to U1305 are not retrieved, go to step  7 .
  4. If DTCs U1300, U1301 or U1305 are retrieved from any module, go to next step. If DTCs U1300, U1301 or U1305 are not retrieved from any module, go to step  6 .
    5. NOTE: Turn ignition switch to RUN position, when testing for a short to voltage. Use DVOM MIN/MAX function to capture intermittent conditions.
  5. Inspect Purple wire for an intermittent short to ground or short to voltage between DLC and suspect module. See DATA LINK CONNECTORS article in WIRING DIAGRAMS. If problem does not exist, go to next step. If problem exists, repair Purple wire as necessary. After repair, go to step  18 .
  6. If DTC U1000 and U1255 are displayed, perform DTC U1000 & U1255: CLASS 2 COMMUNICATION MALFUNCTION  under DIAGNOSTIC TESTS. If DTC U1001-U1255 is displayed, perform DTC U1001-U1254: LOSS OF XXX COMMUNICATION  under DIAGNOSTIC TESTS.
  7. Diagnose non-communicating module by performing DTC U1001-U1254: LOSS OF XXX COMMUNICATION  under DIAGNOSTIC TESTS. After repair procedure has been complete, perform appropriate diagnostic system check for suspect system. See BODY CONTROL SYSTEM DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  8. Turn ignition switch to OFF position. Disconnect scan tool from DLC. Inspect DLC for poor connections and terminal tension. If problem does not exist, go to next step. If problem exists, repair DLC as necessary. After repair, perform appropriate diagnostic system check for suspect system. See BODY CONTROL SYSTEM DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  9. Inspect ground circuits for an open or high resistance between ground and DLC terminals No. 4 (Black wire) and 5 (Black/White wire), individually. See DATA LINK CONNECTORS article in WIRING DIAGRAMS. If problem does not exist, go to next step. If problem exists, repair Black wire and/or Black/White wire as necessary. After repair, perform appropriate diagnostic system check for suspect system. See BODY CONTROL SYSTEM DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  10. Inspect Purple wire for an open, high resistance, short to ground or short to voltage between DLC terminal No. 2 and Dash Integration Module (DIM) harness connector C2 terminal A12 and Instrument Panel Module (IPM) harness connector C1 terminal C8, individually. See appropriate DATA LINK CONNECTORS article. If problem does not exist, go to next step. If problem exists, repair Purple wire as necessary. After repair, perform appropriate diagnostic system check for suspect system. See DIAGNOSTIC SYSTEM CHECK  table under SELF-DIAGNOSTIC SYSTEM.See BODY CONTROL SYSTEM DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
    11. NOTE: Before proceeding with this test step, refer to DATA LINK CONNECTORS article in WIRING DIAGRAMS. DO NOT disconnect module furthest from DLC to perform this test.
  11. Turn ignition switch to OFF position. Split class 2 serial data circuit in half by disconnecting 2 module harness connectors, to help isolate location of fault. DLC must remain connected to at least one module. Turn ignition switch to RUN position. Using scan tool, attempt to communicate with modules still connected to DLC. If scan tool does not communicate with any remaining modules, go to next step. If scan tool communicates with any remaining module, go to step  13 .
    12. NOTE: If fault is located within portion of class 2 serial data circuit still connected to DLC, perform the following, one module at a time starting at module furthest from DLC. Continue this for each module on class 2 serial data circuit still connected to DLC.
  12. Turn ignition switch to OFF position. Disconnect furthest module from DLC which is still connected to class 2 serial data circuit. Turn ignition switch to RUN position. Using scan tool, attempt to communicate with any module still connected to DLC. Continue this procedure until all modules are communicating. If scan tool does not communicate with modules, go to next step. If scan tool communicates with modules, go to step  15 .
    13. NOTE: If fault is located within portion of the class 2 serial data circuit that is not connected to DLC. Connect one of the modules that was disconnected to split serial data circuit. Perform the following, one module at a time, starting at module furthest from DLC, for each module on class 2 serial data circuit now attached to DLC. Continue this procedure until all modules are communicating.
  13. Turn ignition switch to OFF position. Disconnect furthest module from DLC still connected to class 2 serial data circuit. Turn ignition switch to RUN position. Using scan tool, attempt to communicate with any module still connected to DLC. If scan tool does not communicate with any module, go to next step. If scan tool communicates with any modules, go to step  18 .
  14. Repair class 2 serial data circuits and in-line harness connectors to last module connected in branch being diagnosed. After repair, go to step  18 .
  15. Inspect Purple wire for a short to ground or short to voltage between DLC and last module disconnected. See DATA LINK CONNECTORS article in WIRING DIAGRAMS. Turn ignition switch to RUN position to test for short to voltage. If problem does not exist, go to next step. If problem exists, repair Purple wire as necessary. After repair, go to step  18 .
  16. Inspect harness connector of last module disconnected for poor connections and terminal tension. If problem does not exist, go to next step. If problem exists, repair suspect harness connector as necessary. After repair, go to step  18 .
  17. Replace suspect module which was last disconnected. Program suspect module, if necessary. See PROGRAMMING  . After repair, go to next step.
    18. NOTE: Scan tool may require a power up reset, to restore power, before communication will occur, due to a short in class 2 serial data circuit. Turn off or disconnect scan tool before displaying DTCs.
  18. Connect all modules. Connect scan tool to DLC. Turn ignition switch to RUN position, and wait 10 seconds. Using scan tool, select DISPLAY DTCs function for each module. Record all displayed DTCs, and status. If scan tool does not display any DTCs which begin with "U" and are current, go to next step. If scan tool displays any DTCs which begin with "U" and are current, go to step  20 .
  19. If scan tool displays any DTCs which do not begin with "U", go to next step. If scan tool does not display any DTCs which do not begin with "U", go to step  21 .
  20. Perform appropriate test in accordance with DTC retrieved. See DIAGNOSTIC TROUBLE CODE DEFINITIONS  . After diagnosis, go to next step.
  21. If all DTCs are not diagnosed, go to step  20 . If all DTCs are diagnosed, go to next step.
  22. Using scan tool, clear DTCs. System is okay at this time.
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