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DTC codes / U06xx · Network communication / U0699

U0699Lost Communication With Coolant Pump F

U0699 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 coolant pump F, which is typically an electrically driven auxiliary or main coolant pump. The module monitoring the pump expects regular status messages or a valid feedback signal from the pump, and when those messages stop arriving within the programmed timeout window, it stores this code and may illuminate the warning light.

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 message on the dashboard.
  • Often no symptoms besides the warning light, especially if the pump is a secondary unit and the engine's mechanical pump still provides adequate cooling.
  • Elevated engine or inverter coolant temperatures if the failed pump is the primary circulation source for the engine or hybrid system.
  • Reduced cabin heat or inconsistent heater performance on vehicles that use the electric coolant pump for climate control flow.
  • A noticeable drop in fuel economy or power if the powertrain control module limits output to protect the engine or battery from overheating.
  • Intermittent warning light operation that comes and goes with vibration, moisture, or temperature changes at the pump connector.

Common causes, most likely first

  1. A failed electric coolant pump motor or internal control board that no longer communicates on the network.
  2. Damaged, corroded, or disconnected wiring and connectors at the pump, especially where the harness passes near heat sources or road splash.
  3. Blown fuse or tripped relay in the pump's dedicated power circuit, leaving the pump unpowered and silent on the bus.
  4. A CAN bus fault such as a shorted or open data line between the pump and the module that monitors it, often caused by chafed harness insulation.
  5. Low system voltage or a weak battery that causes the pump's electronics to drop offline intermittently.
  6. A software or calibration issue in the control module that falsely reports lost communication despite a healthy pump.
  7. Coolant contamination or debris that seizes the pump rotor, causing the pump to shut down and stop transmitting status messages.

How to diagnose and fix it

  1. Verify battery voltage and charging system health, then clear the code and test-drive to see whether U0699 returns immediately or only under specific conditions.
  2. Inspect the coolant pump connector and harness for corrosion, loose pins, chafed wires, and heat damage, repairing any obvious wiring faults before replacing parts.
  3. Check the pump's dedicated fuse and relay, confirming power and ground at the pump connector with the ignition on and the pump commanded on.
  4. Measure the CAN bus data lines at the pump connector for correct voltage and resistance, looking for a short to ground, short to power, or open circuit.
  5. Command the coolant pump on with a scan tool and listen for operation while watching live data for pump speed or status feedback to confirm whether the pump responds.
  6. If power, ground, and network signals are all correct but the pump does not communicate or run, replace the electric coolant pump and bleed the cooling system properly.
  7. After repair, clear all codes, perform any required pump adaptation or coolant bleed routine, and verify that U0699 does not return during a complete drive cycle.

Why a silent pump sets U0699

  • Many vehicles use the electric coolant pump for charge air cooling or hybrid battery thermal management, so a failed pump can cause derating or shutdown without ever overheating the engine itself.
  • A pump that spins freely by hand can still set U0699 because the internal electronics or position sensor has failed, so mechanical freedom does not prove communication health.
  • Technicians often replace the pump only to find a corroded ground splice or a chafed harness behind the radiator that was the real cause of the lost communication.
  • Aftermarket pumps with incorrect software or wiring adapters are a common source of repeat U0699 codes on vehicles that require a specific communication protocol.
  • A low or failing battery can cause multiple U-codes including U0699, so always check voltage and charging before condemning the pump.

Can I keep driving with U0699?

You can usually drive a short distance to a repair shop if the temperature gauge stays normal and the warning is the only symptom, but avoid heavy loads, towing, or long trips. If the engine or hybrid system temperature rises or the vehicle enters reduced power mode, stop safely and have it towed.

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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