U0647: Lost Communication With Motor Electronics Coolant Pump B

What it means

A control module has stopped receiving expected network messages from motor electronics coolant pump B. The effect on motor electronics 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

Motor electronics coolant pump B circulates coolant for part of the vehicle’s motor-electronics cooling system. U0647 sets when a control module stops receiving expected network messages from pump B, so the system may not know whether this pump is operating as commanded.

Common causes

Most likely first.

1. Bus wiring open or shorted
2. Module without power or ground
3. Module failed

Symptoms

• Warning light or message related to the affected system
• Motor electronics cooling or vehicle performance may be affected

How to diagnose it

1. Scan all modules and record freeze-frame data, including any motor-electronics temperature, cooling, or pump codes that help distinguish pump B’s fault.
2. Check live data for pump B status and motor-electronics temperatures, looking for missing pump data or temperatures that are rising.
3. With the vehicle safely powered down as specified by the manufacturer, inspect pump B’s connector and accessible network wiring for damage or corrosion.
4. Check pump B’s module power and ground circuits against the manufacturer’s specification.
5. Test the network wiring serving pump B for opens or shorts using the vehicle wiring information.
6. If the wiring and supplies pass, verify pump B communication and operation before replacing its module.

Common fixes

• Reconnect or clean the motor electronics coolant pump B connector.
• Repair damaged network wiring to pump B.
• Restore the pump B module’s power or ground supply.
• Replace pump B if its circuits and network connection are sound but communication does not return.

Can I keep driving?

If a cooling warning, rising temperature, or reduced-power message appears, stop safely and follow the vehicle’s instructions; continued driving may overheat motor electronics. Avoid continued use until pump B communication and cooling operation are checked.