Lost Communication With ECM/PCM B
Your vehicle's main computer (ECM/PCM B) has lost its communication link with another control module, similar to two phones unable to reach each other. This prevents proper data sharing needed for engine and vehicle operation.
The ECM continuously monitors CAN bus communication signals from secondary modules (transmission control, ABS, etc.) at regular intervals. When expected messages fail to arrive within timeout thresholds, the ECU logs a communication fault and may enter limp mode.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| CAN Bus Message Timeout | Messages received every 10-100ms | No message for >200ms from ECM/PCM B |
| CAN Bus Signal Voltage | 0-5V with proper CAN protocol | No valid CAN signal detected |
Code U0115 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, U0115 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.