U063B: Lost Communication With Coolant Bypass Valve Actuator A

What it means

A control module has stopped receiving expected network messages from coolant bypass valve actuator A. The effect on coolant routing depends on the vehicle's system design.

At a glance

• Usually lights the warning light of the system that lost communication

How it works

Coolant bypass valve actuator A helps route coolant through the paths selected by the vehicle’s thermal management system. A control module expects the actuator or its controller to send status messages over the network. U063B sets when those messages from actuator A are lost, so the module may not know whether coolant routing is correct.

Common causes

Most likely first.

1. Bus wiring open or shorted
2. Module without power or ground
3. Module failed

Symptoms

• Warning light or message related to the affected system
• Cooling or temperature control may be affected

How to diagnose it

1. Scan all modules and review freeze-frame data for communication faults that occurred with the coolant bypass valve actuator A message loss.
2. Check live data for actuator A status and commanded position, if available, for a missing reading or a response that does not update.
3. Inspect actuator A’s connector and network wiring for damage, corrosion, loose terminals, or signs of coolant intrusion.
4. Check the actuator or controller’s power and ground against the manufacturer’s specification.
5. Test the network wiring for opens or shorts and assess the actuator’s reporting module if wiring and supplies are sound.

Common fixes

• Reconnect or clean and secure actuator A’s network connector.
• Repair damaged network wiring to coolant bypass valve actuator A.
• Restore the actuator or its controller’s power or ground.
• Replace the failed actuator reporting module after confirming its circuits are sound.

Can I keep driving?

If the vehicle shows a coolant or temperature warning, avoid long trips, heavy loads, and hard driving because incorrect coolant routing can cause overheating or poor temperature control. Stop if the engine temperature rises or a warning appears.