What Does P0644 Mean?
The PCM/ECM has detected a fault in the driver display serial communication circuit. This is the data link between the engine control module and the driver information display or instrument cluster. When this circuit fails, the instrument cluster may not receive engine data for display. The driver may notice missing or frozen readings for RPM, coolant temperature, fuel economy data, or other engine-related information on the dashboard display.
Common Causes
30%
Damaged or corroded serial communication wiring between PCM and instrument cluster
25%
Faulty instrument cluster not responding on the serial bus
18%
PCM/ECM serial output driver failure
15%
Connector corrosion or loose connection at the PCM or instrument cluster
12%
Network bus interference from aftermarket electronics or a faulty module on the bus
Diagnostic Steps
1
Check the instrument cluster for any missing, frozen, or erratic readings. Note which specific displays are affected to help identify the communication path.
2
Inspect the serial communication circuit wiring and connectors at both the PCM and instrument cluster. Look for corrosion, bent pins, or loose connections.
3
Using the scan tool, check for communication errors or U-codes (network communication DTCs) that may accompany P0644 and point to a broader network issue.
4
If the vehicle uses CAN bus, measure the CAN High and CAN Low voltages at the instrument cluster connector. CAN-H should idle at approximately 2.5V and pulse to 3.5V; CAN-L should idle at approximately 2.5V and pulse to 1.5V.
5
Disconnect any aftermarket electronics (remote starters, alarm systems, GPS trackers) that may be tapping into the communication bus and see if the code clears.
Estimated Repair Cost
$80 - $600
Parts + labor, varies by vehicle and location
The PCM/ECM has detected a fault in the driver display serial communication circuit. This is the data link between the engine control module and the driver information display or instrument cluster. When this circuit fails, the instrument cluster may not receive engine data for display. The driver m...
The most common cause of P0644 (Driver Display Serial Communication Circuit) is: Damaged or corroded serial communication wiring between PCM and instrument cluster
Typical repair costs for P0644 range from $80 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
The vehicle is generally safe to drive, but you may lose visibility of important information like coolant temperature, RPM, or warning indicators. If critical gauges are not functioning, you will not be alerted to overheating or other dangerous conditions. Monitor the engine closely by feel and sound and schedule diagnosis promptly.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0644 to identify the root cause.
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Quick Info
Category
Powertrain
System
Communication / Instrument System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
