Lost Communication With Telephone Control Module
Your car's main computer lost contact with the telephone/telematics control module, like a dropped phone call between two people trying to communicate. This is a network communication failure between vehicle control modules.
The main ECU monitors CAN bus communication signals to and from the Telephone Control Module at regular intervals. When expected messages fail to arrive within a timeout window, the ECU logs this fault. The system checks for valid data packets and handshake responses from the module.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| CAN Bus Message Timeout | Message received every 100-500ms | No response for >1000ms |
| Module Acknowledgment | Valid CAN ID response present | Missing or invalid response packets |
Code U0197 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, U0197 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.