Lost Communication With All Terrain Control Module
Your vehicle's main computer has lost the ability to talk to the all-terrain control module, similar to a radio losing its signal. This prevents the system from managing traction control and stability features.
The ECM continuously monitors CAN bus communication with the all-terrain control module through periodic handshake messages. When no valid response is received within a defined timeout window (typically 100-500ms), the fault is triggered. The ECM expects acknowledgment frames at regular intervals to confirm module presence and functionality.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| CAN Bus Response Time | 50-150ms | No response or >500ms timeout |
| Message Frequency | Every 10-100ms | Missing or irregular messages |
Code U0138 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, U0138 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.