Error Code P0644 is defined as Driver Display Serial Communication Circuit, which means there’s an error detected in the communication between multiple control modules, likely caused by a faulty driver or bad electrical connection in the PCM.
This is a generic trouble code, meaning it applies to all cars equipped with the OBD-II system, especially those made since 1996 up to present. This includes models from Audi, BMW, Ford, General Motors, Jaguar, Mercedes Benz, Volkswagen, etc. Specifications on the definition, troubleshooting, and repairs, of course, vary from make, model, and power configuration.
When Error Code P0644 appears, this means the PCM (powertrain control module, also known as ECM or engine control module in other 2019 Ford Ranger makes) has detected a malfunction in the serial data control circuit of the driver display system.
For most cars, the driver display refers to the dash-mounted LCD monitor. For some cars, it is the heads-up display that appears on the driver’s side windshield.
Because of the limitations in cost and space associated in manufacturing most cars, the communication between the PCM and other onboard controllers is a serial data communication. This means bytes of data are sequentially transferred, one byte at a time.
All of the onboard serial data communication is carried out through the CAN (controller area network), which is basically an assembly of connectors and wirings inside the harness. It’s a uniform for a specific automobile type, making it possible to use a common set of controllers, actuators, sensors, and a single type of diagnostic system (OBD-II).
If the PCM (or any other onboard controllers) determines a malfunction in the driver display serial data communication circuit, then Error Code P0644 will be stored, while simultaneously activate the Check Engine light. For some cars, it may require multiple drive cycles for the Check Engine light to activate.
Vehicles with engine and transmission performance issues result in a wide variety of drivability problems, such as:
Other stored codes may be present as well.
Serial data communication codes can be challenging to diagnose accurately, but there are several tools that can definitely help for preliminary tests. These tools are pretty basic, namely diagnostic scanner and 2019 Ford Ranger information source.
The 2019 Ford Ranger information source is for the TSB (technical service bulleting) of the fault code, or at least factors parallel to the condition, such as your 2019 Ford Ranger , engine size, codes stored, symptoms, etc. If you can find applicable TSB information for this code, then it helps for a more accurate diagnosis.
Start your diagnosis by connecting the diagnostic scanner to your 2019 Ford Ranger ’s diagnostic port. Retrieve all codes stored, including freeze frame data. Write this information down. Then, clear the codes and then take your 2019 Ford Ranger for a test drive until one of the two scenarios happen:
If the first scenario happens, then you have an intermittent code condition, which means you will have to wait for the problem to get worse before you can diagnose it more accurately.
If the second scenario happens, then you need to inspect all related connectors and wirings. Repair as needed
Check the PCM power supply fuses and relays as well, and of course, repair or replace any damaged component as needed.
If you find no problems in your visual inspection, then you will have to test controller grounds, and repair as needed.
Depending on your diagnosis, common repairs for this code include:
If the PCM has both ground and voltage at the right terminals, then you can suspect damaged or crashed monitor, or PCM programming error. In which case, use a DVOM (digital volt ohmmeter) to test voltage and ground to the PCM and other controllers.