Data Output Link Circuit Failure
The ECU cannot communicate properly with a data output module or circuit, like a radio losing its signal. This is typically a wiring or connector issue preventing the engine computer from sending diagnostic information.
The ECU monitors the data link circuit (often CAN bus or similar communication line) for proper voltage levels and signal integrity. It detects open circuits, shorts, or signal dropout when the circuit fails to respond or maintain proper communication protocol.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Data Link Voltage | 5V reference or CAN signal oscillation 0-5V | No voltage, continuous 0V, or no signal transitions |
| Signal Response Time | Communication within protocol timing | No response or timeout on data requests |
Code P1639 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, P1639 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.