P0644 code meaning
Driver Display Serial Communication Circuit
What P0644 means
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.
P0644 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor1 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0644
- Warning message or lamp (depending on the maker)
- Information in the driver display missing, frozen or jumping
- Display stays dark
Common causes of P0644
- Most likelyWire or connector between module and receiver open, corroded or shorted
- PossibleDisplay or instrument cluster faulty or without supply (fuse, ground)
- Less likelyLow system voltage during cranking
- Less likelyOutput driver in the module faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Driver displaySerial data lineEngine control module
What each part of P0644 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 6 | Area: computer (engine control module) and output circuits. |
| 44 | The exact fault in that area. |
What to do next
- Note P0644 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0644
What does P0644 mean?
P0644 means "Driver Display Serial Communication Circuit". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P0644?
P0644 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will P0644 fail an emissions test?
P0644 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is P0644 to fix?
Difficulty: medium. A typical repair takes 1 to 3 hours of work. This is a job for a workshop.
Will P0644 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.