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Theft Deterrent Diagnostic System Check

WARNING: This page is about a different car, the 2001 GMC Safari and 2001 Chevrolet Astro. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: Presence of DTCs which begin with "U" indicate some other module on class 2 serial data line is not communicating.
  1. Connect scan tool to Data Link Connector (DLC). DLC is located under left side of instrument panel. If scan tool powers up, go to next step. If scan tool does not power up, go to TEST E: SCAN TOOL DOES NOT POWER UP  under SYSTEM TESTS.
  2. Turn ignition switch to RUN position. Attempt to establish communication with Body Control Module (BCM), Instrument Panel Cluster (IPC), Powertrain Control Module (PCM) and Theft Deterrent Control Module (VTD). If scan tool communicates with all modules, go to next step. If scan tool does not communicate with all modules, go to TEST D: SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE  under SYSTEM TESTS.
    3. NOTE: Engine may start during following step. Turn ignition switch to OFF position as soon as you have observed crank power mode.
  3. Using scan tool, access class 2 power mode from diagnostic circuit check function. Rotate ignition switch through all positions while observing ignition switch power mode parameter on scan tool. If ignition switch parameter reading matches ignition switch position for all switch positions, go to next step. If ignition switch parameter reading does not match ignition switch position for all switch positions, go to POWER MODE MISMATCH  under SYSTEM TESTS.
  4. Using scan tool, select DISPLAY DTCS function and retrieve any BCM, IPC, PCM or VTD DTCs. If scan tool displays any DTCs, go to next step. If scan tool does not display, any DTCs, go to step  6 .
  5. Momentarily rotate ignition switch to CRANK (do not start vehicle). Release ignition switch to ON position. With a scan tool, observe Passlock Code in Body Control Module Security Data list. If scan tool does display OPEN, go to DTC B2958. If scan tool does not displays DTC B2958, repair theft deterrent system by symptom. See appropriate ANTI-THEFT SYSTEMS article.
  6. IF scan tool displays any DTCs which begins with a "U", go to TEST D: SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE  under SYSTEM TESTS.
  7. If scan tool does not display DTC P0601, P0602, or P0604 go to next step. If scan tool displays DTC P0601, P0602, or P0604, repair powertrain concern. See appropriate SELF-DIAGNOSTICS article in ENGINE PERFORMANCE.
  8. If scan tool displays DTC B1000, go to DTC B1000: BODY CONTROL MODULE INTERNAL MALFUNCTION  under DIAGNOSTIC TESTS. If scan tool displays any other DTCs, go to next step.
  9. If scan tool displays DTC B1637, repair engine electrical concern. See appropriate GENERATORS & REGULATORS article in STARTING & CHARGING SYSTEMS. If scan tool displays any other DTCs, perform appropriate test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS  .
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