U02AB: Lost Communication With Vehicle Thermal Management Control Module

What it means

The vehicle bus reports loss of communication with the vehicle thermal management module. Coordination of engine, battery and cabin cooling/heating loops is lost; sub-modules fall back to local control.

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

The vehicle thermal management control module coordinates cooling and heating across engine, battery, and cabin circuits. U02AB sets when the network stops receiving its messages, so those loops may lose central coordination and some may fall back to local control.

Common causes

Most likely first.

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

Symptoms

• Multiple warning lights may illuminate
• Affected modules may go into limp mode or shut down
• Specific functions inoperative depending on module
• Diagnostic tools may show communication faults

How to diagnose it

1. Scan all modules and record freeze-frame data to identify related engine, battery, cabin climate, or network codes.
2. Review live temperatures and thermal-system status to see which engine, battery, or cabin functions have lost coordination.
3. Inspect the thermal management module connector and harness for loose pins, corrosion, coolant contamination, or physical damage.
4. Check the module's power and ground using the manufacturer's wiring information and test conditions.
5. Test its network wiring for opens, shorts, or poor connections according to the manufacturer's procedure.
6. If power, ground, and network wiring pass, confirm module failure before replacement and follow the manufacturer's configuration procedure.

Common fixes

• Reconnect or repair a loose or corroded thermal management module connector.
• Repair damaged wiring or a poor network connection at the module.
• Restore the module's power or ground supply.
• Replace and configure the thermal management control module if testing confirms failure.

Can I keep driving?

Engine or battery cooling and heating may be limited, and the vehicle may reduce power to protect components. Avoid strenuous driving if temperatures rise or a thermal warning appears, and stop safely if the vehicle reports overheating.