Lost Communication With Vehicle Security Control Module
Your car's main computer lost its connection to the security/anti-theft control module, like two phones that can't text each other anymore. This prevents proper communication between systems that control engine start and theft prevention.
The ECM continuously monitors CAN bus communication signals from the security control module for valid handshake messages within expected timeframes. When no valid security module response is received within 100-500ms of a query, the ECM interprets this as lost communication and triggers the fault. The system enforces this as a safety feature to prevent unauthorized engine operation.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| CAN Bus Response Time | 50-200ms message receipt | No response or >500ms delay |
| Security Module Heartbeat | Valid message every 10-100ms | Missing or corrupted heartbeat signal |
Code U0168 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, U0168 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.