P0644Driver Display Serial Communication Circuit
- Generic OBD-II code · Powertrain
- How the car detects it
- P0644 concerns a dedicated serial line on which the engine module sends values or warnings to a driver display or information display – not the general vehicle CAN bus. The module reports missing or invalid communication on that line (open, short, display not answering); CARB requires digital outputs to be checked for communication faults. GM Europe's 2010 Saab, for example, passes engine data such as fuel level over CAN to the body module and on to the instrument unit and information display – where such data runs on the bus, a failure is reported as a U code (e.g. U0155) instead. No manufacturer document available to us uses this code; the description follows CARB and the component. Displays then show missing, frozen or jumping information; the engine runs normally.
- What you may notice
- Warning message or lamp (depending on the maker)
- Information in the driver display missing, frozen or jumping
- Display stays dark
- Likely causes
- LikelyWire or connector between module and receiver open, corroded or shorted
- PossibleDisplay or instrument cluster faulty or without supply (fuse, ground)
- RareLow system voltage during cranking
- RareOutput driver in the module faulty
- Repair
- Medium · Usually a job for a workshop.Typical cost: €80 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.