GM Passlock Security Module

GM Passlock Anti-Theft Security Module (SM) — Troubleshooting Guide (SKU Group)

Important: Use this guide if you reinstalled your repaired (GM Passlock Anti-Theft Security Module) and the problem is still happening.
Important: Please do not open/disassemble the module or probe/force connector pins (terminal damage can cause new faults).

• Step 1: Confirm the symptom is Passlock-related
  • Watch the SECURITY light behavior while cranking (flashing/solid can indicate an anti-theft lockout).
  • Note if the engine starts and stalls after 1–2 seconds (classic anti-theft fuel enable issue).
• Step 2: Battery voltage and grounds
  • Fully charge the battery and confirm clean/tight battery terminals.
  • Verify engine block-to-chassis ground straps are intact (low voltage can trigger false theft events).
• Step 3: Check all related fuses
  • Check fuses labeled SECURITY / THEFT / BCM / IGN / CRANK / PCM / RADIO (names vary by model).
  • Don’t just visually inspect—use a test light or meter on both sides of the fuse.
• Step 4: Inspect the module connector and mounting area
  • Inspect for bent pins, pushed-back terminals, corrosion/green residue, or moisture.
  • Make sure the connector is fully seated and locked (partial engagement is very common).
• Step 5: Scan the vehicle for theft/BCM/PCM codes
  • Pull codes from BCM, PCM, and Theft Deterrent/Passlock (tool wording varies).
  • If you see lots of low-voltage/history codes, resolve power/ground first and re-scan.
• Step 6: Rule out the most common root cause (ignition cylinder sensor/wiring)
  • If the issue is intermittent, worsens with steering column movement, or happens after column work:
    • Inspect the ignition switch/cylinder area for loose connectors or rubbed-through wiring.
    • Check for aftermarket remote start/alarm splices (these frequently cause Passlock faults).
• Step 7: Perform the relearn only if needed
  • If the SECURITY light indicates a lockout after parts were replaced or battery went dead, a relearn may be required.
  • Use the OEM scan tool procedure when available; avoid repeated guesswork cycles that drain the battery.
• Step 8: If it still won’t start
  • If SECURITY behavior is normal but it still won’t run, shift focus to fuel pressure, crank signal, and PCM power/grounds—not all “no start” complaints are theft-related.