Gear Shift Module Communication Circuit
Your transmission's control module can't communicate with the main engine computer, like a radio that's lost its signal. This breaks the connection needed for smooth gear shifting.
The ECM monitors the CAN bus signal from the Transmission Control Module (TCM) at regular intervals. It expects valid data packets within specific timing windows. If communication drops or becomes corrupted for a threshold duration, the fault is triggered.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| CAN Bus Signal Timeout | TCM data received every 10-50ms | No valid TCM message for >500ms |
| Data Checksum Validity | Checksum matches expected value | Checksum mismatch or corrupt message |
Code P0860 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, P0860 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.