What it means
A control module has stopped receiving expected network messages from coolant pump D. The effect on cooling depends on the vehicle's system design.
At a glance
- Usually lights the warning light of the system that lost communication
- The engine or gearbox may go into limp mode
How it works
Coolant pump D moves coolant through the cooling circuit it serves. U0649 sets when a control module stops receiving expected network messages from pump D, so pump status may be unavailable and cooling performance may be affected.
Common causes
Most likely first.
- Bus wiring open or shorted
- Module without power or ground
- Module failed
Symptoms
- Warning light or message related to the affected system
- Cooling system may not operate as intended
How to diagnose it
- Scan all modules and record freeze-frame data, including any coolant-temperature, pump D, or network codes.
- Check live data for pump D status and the temperatures of the systems it serves, looking for missing pump data or abnormal temperature rise.
- With the vehicle safely powered down as specified by the manufacturer, inspect pump D’s connector and accessible network wiring for corrosion, looseness, or damage.
- Check the pump D module’s power and ground circuits against the manufacturer’s specification.
- Test the network wiring to pump D for opens or shorts using the vehicle wiring information.
- If the wiring and supplies pass, verify communication and pump operation before replacing the module.
Common fixes
- Reconnect or clean the coolant pump D connector.
- Repair damaged network wiring to pump D.
- Restore the pump D module’s power or ground supply.
- Replace pump D if its power, ground, and network circuits are sound but communication remains absent.
Can I keep driving?
A cooling warning or rising temperature calls for stopping in a safe place and following the vehicle’s instructions; continued driving can cause overheating. Avoid using the vehicle until cooling operation is checked if temperature warnings persist.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.