P0644

What it means

P0644 is the generic SAE J2012 code for a fault in the serial communication circuit between the control module and the driver display, such as the instrument cluster or message centre. The module that sets it saw missing, corrupted or out-of-range data on the link to the display. How the link is wired and which module logs the code depends on the make and model.

Symptoms

• Warning light for the engine management system on
• Instrument cluster or driver display blank, dim or flickering
• Gauges such as the speedometer, rev counter or temperature reading wrongly or not at all
• Warning messages missing or showing incorrectly
• Other communication or network fault codes stored alongside it
• Intermittent display faults that come and go with vibration or temperature

Possible causes

• Damaged, corroded or loose wiring or connectors in the serial link between the control module and the displaylikely
• Low battery voltage, poor power or earth supply to the display or control modulelikely
• Fault inside the instrument cluster or driver display unitpossible
• Water ingress or corrosion at a module connector or junctionpossible
• Fault in the control module that sends or receives the display datapossible
• Outdated or faulty software in the display or control module, where the manufacturer has a known issuerare
• Poorly fitted aftermarket electrical accessory interfering with the data linkrare

How to diagnose

1. Read all stored codes and freeze frame data, noting any other communication or network codes and whether P0644 is current or historic
2. Check battery condition and charging voltage, as low voltage commonly causes false communication faults
3. Visually inspect the wiring and connectors to the instrument cluster and relevant control module for damage, chafing, moisture and corrosion
4. Check the fuses, power supplies and earth connections for the display and the control module
5. Check the display's operation and see whether the fault changes when the loom is gently wiggled
6. Using the manufacturer's wiring diagram for the model, test the serial circuit for continuity, short to earth, short to voltage and resistance
7. Check for any aftermarket accessories wired into the network and temporarily disconnect them to see if the fault clears
8. Check for manufacturer software updates or technical bulletins for the model, then test or substitute the display or module only after wiring and power are proven

How to fix

• Repair or replace damaged wiring and clean or renew corroded connectors and terminals
• Charge or replace a weak battery and repair any charging or earthing faults
• Restore correct power and earth supply by repairing the fuse, relay or connection fault
• Repair or replace a faulty instrument cluster or display, then program or code it as the manufacturer requires
• Repair or replace a faulty control module and set it up as required
• Update the software in the module if an outdated version is a known cause for that model

Can I keep driving?

Nearby codes

• P0643GenericSensor Reference Voltage A Circuit High
• P0645GenericA/C Clutch Relay Control Circuit