ECM/TCM Serial Communication Error
The engine control module and transmission control module can't communicate with each other properly, like two walkie-talkies with a dead battery. This breaks the coordination needed for smooth engine and transmission operation.
The ECM and TCM exchange serial data through the CAN bus or dedicated communication lines at specific intervals and voltage levels. The system monitors for signal loss, corruption, or timing failures in this handshake protocol. If acknowledgment signals don't arrive within the expected window or voltage levels drop below threshold, a communication error is flagged.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| CAN Bus Voltage | 2.5-3.5V (recessive state) | <0.5V or >5.0V for extended duration |
| Message Response Time | <100ms between transmit and acknowledge | >500ms or no response |
Code P1606 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, P1606 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.