What it means
A control module has stopped receiving expected network messages from hybrid/EV battery pack coolant control valve B. The effect on battery coolant routing depends on the vehicle's system design.
At a glance
- Usually lights the warning light of the system that lost communication
- The engine or gearbox may go into limp mode
How it works
Hybrid/EV battery pack coolant control valve B routes coolant within a battery thermal-management system and sends status through a networked module. U0637 sets when expected messages from valve B are lost, specifically affecting valve B's communication rather than valve A's.
Common causes
Most likely first.
- Bus wiring open or shorted
- Module without power or ground
- Module failed
Symptoms
- Warning light or message related to the affected system
- Battery cooling may not operate as intended
How to diagnose it
- Capture freeze-frame data and scan all modules for battery thermal-management, valve B, network, and supply codes.
- Review live data for valve B communication and commanded or reported state, comparing with valve A if the system exposes both.
- Inspect valve B's low-voltage harness and connectors for chafing, corrosion, loose terminals, or signs of coolant entry.
- Verify power and ground at valve B's reporting module using the wiring diagram and manufacturer's specifications.
- If basic checks pass, test the network and evaluate the communicating module according to the manufacturer's hybrid/EV diagnostic procedure.
Common fixes
- Repair damaged or shorted low-voltage communication wiring serving valve B.
- Clean or replace corroded or loose valve B connector terminals.
- Restore a verified power or ground connection at the module communicating valve B.
- Replace the reporting module only after its network circuit and electrical supplies test correctly.
Can I keep driving?
Avoid fast charging and high-load driving if a battery cooling warning or power limit appears. Lost communication with valve B can leave coolant routing unconfirmed, so stop if the vehicle reports battery overheating or another thermal warning.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.