U063D: Lost Communication With Hybrid/EV Electronics Coolant Pump A

What it means

A control module has stopped receiving expected network messages from hybrid/EV electronics coolant pump A. The effect on electronics cooling 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 electronics coolant pump A circulates coolant to help control the temperature of high-voltage electronics. The vehicle network carries pump status to the modules that manage electronics cooling. U063D sets when a module stops receiving expected messages from pump A, which can affect cooling control and may lead to reduced vehicle performance.

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
• Electronics cooling or vehicle performance may be affected

How to diagnose it

1. Scan all modules and review freeze-frame data for related communication or electronics cooling faults.
2. Check live data for pump A status and electronics coolant temperature to see whether the pump’s report is missing and temperatures are rising.
3. Inspect pump A’s network connector and wiring for damage, corrosion, looseness, or coolant contamination.
4. Check power and ground at pump A or its controller against the manufacturer’s specification.
5. Test the network circuit for opens or shorts and evaluate the pump’s reporting module if its wiring and supplies are sound.

Common fixes

• Reconnect or repair a loose or damaged pump A network connector.
• Repair an open or short in the network wiring to pump A.
• Restore power or ground to the pump or controller.
• Replace the failed pump A reporting module after confirming the circuit is intact.

Can I keep driving?

Do not continue driving if the hybrid/EV system displays a temperature warning, limits power, or reports a cooling fault; electronics may overheat and the vehicle may enter reduced-power mode. Stop safely and arrange diagnosis before driving again.