Lost Communication With Telematic Control Module
Your car's main computer lost connection with the telematics module, which handles remote services like OnStar or emergency calling. It's like a phone losing signal to its carrier—the devices are fine, but they can't talk to each other.
The main ECU periodically attempts CAN bus communication handshakes with the Telematic Control Module (TCM) at set intervals. When no acknowledgment is received within the timeout window, a communication fault is flagged. The ECU monitors signal integrity, voltage levels, and data frame responses.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| CAN Bus Communication Timeout | ACK received within 100-500ms | No response for 3+ consecutive attempts |
| Voltage Supply to TCM | 12-14.5V | Below 10V or above 16V |
Code U0198 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, U0198 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.