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DTC codes / U06xx · Network communication / U0672

U0672Lost Communication With Engine Coolant Pump

U0672 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 engine coolant pump module or the pump's integrated control circuit. The computer detected that expected periodic status messages from the coolant pump stopped arriving within the required time window, which sets the code and usually illuminates the check engine light.

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

Symptoms you may notice

  • Check engine light or service vehicle soon message illuminated on the dashboard
  • Often no symptoms besides the warning light, especially if the pump continues running on a default strategy
  • Engine temperature gauge reading higher than normal or fluctuating during idle and low-speed driving
  • Cooling fan running constantly or not engaging at all because the powertrain control module lacks pump status data
  • Reduced engine power or limp-home mode on vehicles that protect the engine when coolant flow is unconfirmed
  • Auxiliary or electric coolant pump not running after engine shutdown, leading to heat soak concerns

Common causes, most likely first

  1. Failed electric coolant pump assembly, including its internal electronics or brushless motor driver
  2. Damaged or corroded wiring harness and connector pins at the coolant pump or its in-line connector
  3. Blown fuse or faulty relay in the coolant pump power supply circuit
  4. Open or shorted CAN bus wiring between the pump module and the network gateway or powertrain control module
  5. Low or unstable system voltage caused by a weak battery or failing alternator, disrupting module communication
  6. Software calibration issue in the pump control module or powertrain control module requiring a reflash
  7. Water intrusion or heat damage at the pump connector causing intermittent communication loss

How to diagnose and fix it

  1. Scan all modules for stored and pending codes, then record freeze-frame data and verify whether other network codes are present
  2. Inspect the coolant pump connector and harness for corrosion, chafing, pushed pins, or signs of coolant wicking into the wiring
  3. Check the coolant pump fuse and relay, and measure battery voltage and charging system output to rule out low-voltage communication faults
  4. Measure CAN bus voltage levels and resistance at the pump connector to confirm the network segment is intact and properly terminated
  5. Command the coolant pump on with a scan tool and observe live data for pump speed, commanded state, and actual current draw
  6. Perform a voltage drop test on the pump power and ground circuits under load to catch high-resistance connections that a simple continuity test misses
  7. Replace the coolant pump only after electrical and network tests confirm the pump module is not responding, then clear codes and verify communication restores

Why the pump may still be running

  • A coolant pump that spins freely and moves coolant can still set U0672 because the code tracks the pump's electronic status messages, not its mechanical output.
  • Low system voltage from a weak battery often sets communication codes like U0672 across several modules, so always check charging system health before condemning the pump.
  • Coolant wicking through the pump harness into the connector is a common hidden cause that looks like a failed pump but is actually a wiring repair.
  • On some vehicles the coolant pump shares a CAN segment with other auxiliary modules, so a single unplugged or failed module can take the pump offline and set this code.
  • Replacing the pump without clearing adaptive learned values or performing a relearn procedure can leave the new pump unrecognized and the code returning.

Can I keep driving with U0672?

You can usually drive a short distance to a repair shop if the temperature gauge stays normal, but avoid heavy loads, towing, and long idles because an unconfirmed coolant pump can lead to overheating. If the temperature gauge climbs or a red overheating warning appears, stop safely and shut the engine off immediately.

Tools that help

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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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