U0168 — Lost Communication With Vehicle Security Control Module

Diagnostic algorithm

1. Confirm the code and note whether it is current or history. Check for related U-codes (bus errors) and freeze frame data.
2. Verify battery state of charge and charging system. Recharge or replace weak battery before in-depth testing.
3. Inspect VSM power feed fuses and fusible links; replace any blown fuses and re-test.
4. Visually inspect connectors and harness at the VSM for corrosion, bent pins, water intrusion or physical damage.
5. Verify good ground(s) for the VSM: disconnect connector and measure continuity to battery negative.
6. With ignition on, measure VSM supply voltage at the module connector; no supply indicates wiring/power issue upstream.
7. Use a scan tool to poll other modules on the same CAN bus. If multiple modules are missing, focus on bus physical layer.
8. Measure CAN_H and CAN_L voltages with respect to ground and with each other; check termination resistance (~60 Ω).
9. Probe for shorts: disconnect suspected modules (after noting configuration) and check whether bus communication is restored.
10. If physical layer tests good but VSM does not respond, try re-seating connector and clearing codes. If persistent, consider replacing or reprogramming the VSM per manufacturer procedures.
11. After any repair or module replacement, perform required programming/initialization and verify all security/key functions and that codes do not return.