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DTC B1491: Ignition Cylinder Tamper Switch Circuit Failure

WARNING: This page is about a different car, the 1997 Lincoln Continental. However, it is still accessible from the selected car via links, so may be relevant.
  1. Repeat Self-Test  - Clear DTC and repeat ON-DEMAND SELF-TEST. If DTC B1491 is still present, go to step 4). If DTC B1491 is not present, go to next step.
  2. Check For Intermittent  - Using scan tool, request PID/DATA MONITOR AND RECORD. Select PID status for IGN_PCH. Access PID LATCH active command. Wiggle wiring harness between LCM and ignition switch. Also, wiggle key in ignition switch. If during wiggle test PID status indicates ON and OFF, repair intermittent open circuit as necessary and retest system. If PID status does not indicate ON and OFF, go to next step.
  3. Ensure Ignition Switch Is Not Sticking  - Using scan tool, request PID status for IGN_PCH. Ensure switch is in OFF position. Wiggle ignition switch several times. If PID status indicates ignition switch is OFF at all times, no problem is indicated at this time. If PID status does not indicate ignition switch is OFF at all times, replace ignition cylinder tamper switch. Retest system.
  4. Check Ignition Cylinder Tamper Switch PID  - Using scan tool, request PID/DATA MONITOR AND RECORD. Select PID status for IGN_PCH. If PID status indicates ON, go to next step. If PID status indicates OFF, replace LCM. Reconnect components and retest system.
  5. Check Switch  - Disconnect ignition switch cylinder tamper switch connector. Measure resistance across switch terminal. If resistance is about 640 ohms, go to next step. If resistance is not about 640 ohms, replace ignition tamper switch. Retest system.
  6. Check Circuit No. 936  - Disconnect LCM C206 connector See Figure . Measure resistance of Dark Green/White wire between terminal No. 20 at LCM wiring harness connector and ignition switch cylinder tamper switch connector. If resistance is 5 ohms or less, go to next step. If resistance is more than 5 ohms, repair open Dark Green/White wire.
  7. Check Circuit No. 339  - Measure resistance of Gray wire between terminal No. 21 at LCM wiring harness connector and ignition switch cylinder tamper switch connector. If resistance is 5 ohms or less, no problem is indicated at this time. If resistance is more than 5 ohms, repair open Gray wire.
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