Technical Description of OBD-II Trouble Code
Malfunction in the Circuit for Driver Display Serial Communication
What does that signify?
This is a generic diagnostic trouble code (DTC) that is applicable to many OBD-II vehicles (1996-newer), including Audi, BMW, General Motors, Ford, Jaguar, Mercedes-Benz, Volkswagen, etc. However, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.
If your OBD-II equipped vehicle has stored a code P0644, it means that the powertrain control module (PCM) has detected a malfunction in the serial data control circuit of the driver display system.
In most cases, the driver display refers to the LCD monitor mounted on the dashboard, but it can also refer to the heads-up display on the driver’s side windshield of certain vehicles.
Due to space and cost limitations in mass-produced vehicles, communication between the PCM and other on-board controllers is done through serial data communication. This means that data is transferred one byte at a time, sequentially.
All on-board serial data communication is carried out using the controller area network (CAN), which is a wiring and connector system formed into a harness. It is standardized for a particular type of automobile, allowing for the use of common controllers, sensors, actuators, and a single diagnostic system (OBD-II).
If the PCM (or another on-board controller) detects a malfunction in the driver display serial data communication circuit, it will store a code P0644 and may illuminate the malfunction indicator lamp (MIL). In most cases, MIL illumination will require multiple ignition cycles with a failure.
A dashboard with multiple LCD screens:
What is the severity of this DTC?
This type of serial data communication code should not cause any drivability or safety issues. However, a code P0644 could be associated with a loss of the driver display, which may be inconvenient but not classified as a severe condition.
What are some of the symptoms of the code?
Symptoms of a P0644 trouble code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P0644 troubleshooting steps?
Diagnosing serial data communication codes can be challenging, but there are several tools that can help with preliminary tests.
A diagnostic scanner and a reliable source of vehicle information will be useful in attempting to diagnose a code P0644.
You can use the source of vehicle information to search for technical service bulletins (TSB) that match your vehicle, engine size, symptoms, and stored codes. If you find a relevant TSB, it may expedite the diagnosis of the code P0644. When dealing with a serial data communication code, finding a relevant TSB can be very helpful.
Start by connecting the scanner to the vehicle diagnostic port and retrieving all stored codes and relevant freeze frame data. Write down this information in case it is needed later (after clearing the codes). Next, clear the codes and test drive the vehicle until one of two scenarios occurs:
A. The code fails to reset and the PCM enters readiness mode
B. The code is reset
If scenario A occurs, you are dealing with an intermittent code and the conditions that caused it may need to worsen before an accurate diagnosis can be made.
If scenario B occurs, visually inspect all related wiring and connectors. Check PCM power supply fuses and relays. Make necessary repairs. If no problems are found, test controller grounds and repair as needed.
If the PCM has proper ground and voltage at the appropriate terminals, suspect that the monitor has crashed or there is a PCM/programming error.
