U0694

Code

Generic U — Network/User

Lost Communication With Hybrid/EV Battery Pack Coolant Pump A

Brand: Generic

Type: U — Network/User

Views: UK: 20 EN: 25 RU: 22

AI status

Completed

ready

Completed 100%

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

Use a scan tool to record all codes, freeze frame, and whether the pump A module appears on the network. Note related U-codes.
Confirm symptom: attempt to command the pump on/off via scan tool (if supported) and observe response/messages.
Visually inspect wiring and connectors at the battery pack and pump for damage, corrosion, or loose terminals; repair as needed.
Check fuses and relays for the pump/module circuit; verify supply voltage at the module connector with ignition on and with pump commanded.
Verify ground integrity: measure resistance between module ground and vehicle chassis (
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.
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.
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.
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.
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.
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