Driver Display Serial Communication Circuit
Your vehicle's dashboard display isn't communicating properly with the engine computer—think of it as a broken phone line between two people trying to talk. The ECU can't send information to show you important warnings or data on your instrument cluster.
The ECU monitors the serial communication bus (typically CAN or LIN protocol) that transmits data to the driver display module. It checks for valid signal voltage levels, message timing, and acknowledgment responses from the display unit. If communication drops below threshold voltage or times out, the fault is triggered.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Bus Voltage Level | 4.5V to 5.5V | Below 4.5V or above 5.5V for extended period |
| Message Response Time | 10-100ms per cycle | No response or timeout exceeding 200ms |
Code P0644 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, P0644 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.