Lost Communication With Fuel Additive Control Module
Your engine's main computer has lost its connection to the fuel additive injection system, like a walkie-talkie losing signal. The system can't communicate to add detergent to your fuel, which may affect engine cleanliness and performance.
The ECM monitors CAN bus communication signals from the Fuel Additive Control Module at regular intervals. When no valid message is received within a set timeout window, the ECM triggers a fault. The module typically sends status and confirmation messages every 50-200 milliseconds.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| CAN Bus Message Timeout | Valid message received every 50-200 ms | No message for >500 ms or communication loss detected |
| Module Handshake Status | Module responding with ACK signals | No ACK received or invalid checksum |
Code U0118 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, U0118 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.