Driver Display Serial Communication Circuit Malfunction
The P0644 code indicates a fault in the serial communication circuit between the instrument cluster (driver display) and other control modules, such as the PCM or BCM. This circuit uses a dedicated serial data line to transmit information like speed, fuel level, and warning lights. When the PCM detects a loss of communication or an invalid signal, it sets this code. Common causes include wiring issues, poor connections, or a faulty instrument cluster.
01. Most Common Causes
- Damaged or corroded wiring/connectors in the serial communication circuit
- Faulty instrument cluster (driver display module)
- Malfunctioning PCM or BCM affecting communication
02. Symptoms You Will Notice
- Instrument cluster gauges or displays not working properly
- Warning lights (check engine, ABS, etc.) staying on or flashing
- Intermittent or complete loss of dashboard functionality
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm the code and check for related codes (e.g., U codes).
Step 2: Visually inspect the wiring and connectors between the instrument cluster and PCM/BCM for damage, corrosion, or loose pins.
Step 3: Test the serial communication circuit for continuity and proper voltage using a multimeter.
Step 4: If wiring is okay, attempt to communicate with the instrument cluster via scan tool; if no response, suspect a faulty cluster.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is generally safe to drive short distances, but you may lose critical dashboard information (speed, fuel, warning lights). Have it diagnosed promptly to avoid potential safety issues.
How much does it cost to fix?▼
Diagnosis typically costs $50-$150. Repair costs vary: wiring repairs $100-$300, instrument cluster replacement $200-$600, or PCM/BCM repair $300-$800.