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Home / DTC / U0694 — Lost Communication With Hybrid/EV Battery Pack Coolant Pump A

U0694 — Lost Communication With Hybrid/EV Battery Pack Coolant Pump A

Detailed page for trouble code U0694.

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Code

U0694

Generic U — Network/User

Lost Communication With Hybrid/EV Battery Pack Coolant Pump A

Brand: Generic
Type: U — Network/User
Views: UK: 15 EN: 17 RU: 18
AI status
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Page language: EN

Causes

  • Faulty or intermittent CAN/LIN network between battery coolant pump module and vehicle control module
  • Open or shorted wiring, damaged connector, or corroded pins at pump/module
  • Blown fuse or failed relay powering the pump module
  • Defective battery pack coolant pump module or pump motor
  • Poor ground connection at pump/module or vehicle chassis ground
  • Software/firmware mismatch or module programming corruption

Symptoms

  • Malfunction Indicator Lamp (MIL) or warning indicator illuminated
  • Battery thermal management disabled or reduced (warnings on dash)
  • Reduced charging rate or charge inhibited by battery management system
  • Unusual battery temperature increase or thermal warnings
  • Possible loss of driveability or entry into limp/limited performance mode
  • No operation from battery coolant pump A when expected

What to check

  • Read all stored and pending DTCs and freeze frame data with a capable scan tool
  • Confirm whether the pump A module is present/listed on the network via scan tool
  • Visually inspect connectors, wiring, and harness for damage, corrosion, or water ingress at pump and battery pack
  • Check fuses and relays that supply the pump/module for continuity and correct operation
  • Verify proper battery/ignition supply voltage and ground at the pump/module connector
  • Perform CAN bus voltage checks and look for activity on CAN high/low with a scope or graphing scan tool

Signal parameters

  • CAN High/CAN Low differential voltage and idle voltages (typically ~2.5 V common mode, ~0.5–2.5 V differential when active)
  • Presence and frequency of pump module messages (messages/sec or ms interval)
  • Module 'alive' or heartbeat signal count
  • Battery coolant pump supply voltage (12 V or high-voltage control feed depending on design)
  • Pump motor current draw (A) when commanded on
  • Ground resistance at module (ohms)

Diagnostic algorithm

  1. Use a scan tool to record all codes, freeze frame, and whether the pump A module appears on the network. Note related U-codes.
  2. Confirm symptom: attempt to command the pump on/off via scan tool (if supported) and observe response/messages.
  3. Visually inspect wiring and connectors at the battery pack and pump for damage, corrosion, or loose terminals; repair as needed.
  4. Check fuses and relays for the pump/module circuit; verify supply voltage at the module connector with ignition on and with pump commanded.
  5. Verify ground integrity: measure resistance between module ground and vehicle chassis (
  6. Probe CAN bus near the module: verify idle voltages and active message traffic with a scope or CAN diagnostic tool. Compare to a known-good segment.
  7. If bus voltages or message traffic are absent/intermittent, trace CAN wiring back toward junctions and other modules, checking continuity and shorts to ground/voltage.
  8. If power, ground, and CAN are good at the module connector but no messages, suspect a failed pump control module. Verify with swap or module bench test if available.
  9. If pump module reports but pump motor does not run, check motor resistance and insulation, relay/power driver, and apply bench 12 V (or follow HV safety procedures) to verify motor operation.
  10. Repair or replace wiring, connector, fuse/relay, pump module or pump motor as indicated. After repair, clear codes and perform a full system test and road test; monitor for reappearance.
  11. Check for software updates or calibration procedures from manufacturer and perform VIN-specific reprogramming if required by repair.

Likely causes

  • Loose or corroded connector at the pump control module
  • Loss of power or ground to the pump module (blown fuse or bad relay)
  • CAN high/low wiring open or shorted near the battery pack
  • Failed pump control module (internal electronics)
  • High module resistance or intermittent wiring causing dropped messages

Fault status

⚠️ Status
Lost communication with Hybrid/EV battery pack coolant pump A control module — no valid messages received. Battery thermal management may be reduced or disabled until communication is restored.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.5-3.0 hours

Similar codes

U0100 U0121 U0141 U0073 U0299
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