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DTC codes / U06xx · Network communication / U0647

U0647Lost Communication With Motor Electronics Coolant Pump B

U0647 is a generic network communication code indicating that a control module on the vehicle's Controller Area Network (CAN) bus has lost contact with the motor electronics coolant pump B, which is an electrically driven auxiliary pump used for battery, inverter, or electronics cooling. The module that sets this code has detected that the pump's dedicated communication messages have stopped arriving within the expected time window, so it flags the circuit as offline rather than reporting a mechanical pump failure.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaNetwork communication

Symptoms you may notice

  • Illumination of the check engine light or a dedicated service warning for the hybrid or electric cooling system
  • Often no symptoms besides the warning light, especially if the pump is only intermittently offline
  • Reduced power or a limp-home mode triggered by the vehicle's electronics thermal management strategy
  • Overheating warnings for the battery pack, inverter, or onboard charger in electrified vehicles
  • A cooling fan that runs continuously or at maximum speed because the module defaults to a safe thermal state
  • Intermittent loss of communication that appears only after the vehicle is fully warmed or during high-load driving

Common causes, most likely first

  1. A failing motor electronics coolant pump B, where the pump's internal electronics stop transmitting on the CAN bus
  2. Damaged, chafed, or corroded wiring in the pump's power, ground, or CAN communication circuit
  3. A loose or corroded connector at the pump or at the module that communicates with it
  4. Low or unstable voltage supplied to the pump, often from a weak battery or a poor ground connection
  5. A software or calibration issue in the control module that monitors the pump, requiring a reflash or update
  6. A failed control module that hosts the pump communication interface, though this is less common than pump or wiring faults
  7. Aftermarket accessories or improper repairs that introduce electrical noise or disrupt the CAN bus

How to diagnose and fix it

  1. Perform a full scan of all modules and record every stored and pending code, then verify that U0647 is current and not history
  2. Inspect the pump connector and the harness along its routing for corrosion, chafing, or loose pins, and check the pump's power and ground with a multimeter under load
  3. Measure the CAN bus voltages at the pump connector with the ignition on to confirm the communication pair is alive and not shorted
  4. Check the vehicle battery state of charge and perform a voltage drop test on the pump's ground circuit to rule out a supply problem
  5. If wiring and power are good, substitute a known-good pump of the same part type or use a bidirectional scan tool to command the pump and observe communication
  6. Check for technical service bulletins or software updates for the module that sets the code, and reflash if a calibration is available
  7. After any repair, clear the codes and drive the vehicle through a complete warm-up and cool-down cycle to confirm the pump communication remains stable

What the coolant pump code really means

  • U0647 is a communication fault, not a direct pump performance code, so replacing the pump without checking the wiring and connectors first is a common and expensive misdiagnosis.
  • On many electrified vehicles the motor electronics coolant pump B runs only during charging or after shutdown, so the code may set without the driver ever seeing an overheating symptom.
  • A weak 12-volt battery can cause intermittent CAN communication loss on the pump circuit, and the pump itself may be perfectly healthy once the battery is replaced.
  • The module that sets U0647 is often not the engine control module but a hybrid or battery energy control module, so scanning only the engine computer can miss the full picture.
  • Aftermarket electrical accessories tapped into the wrong circuit can introduce noise that corrupts the pump's communication messages and sets this code intermittently.

Can I keep driving with U0647?

You can usually drive a short distance to a repair shop if the only symptom is the warning light, but avoid heavy acceleration, sustained high speeds, and fast charging because those conditions demand maximum cooling from the electronics. If the vehicle displays an overheating warning or enters limp mode, stop safely and have it towed rather than continuing.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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