What it means
A control module has stopped receiving expected network messages from coolant pump A. The code indicates a communication fault; the effects depend on the vehicle's cooling 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
Coolant pump A is a networked pump that circulates coolant in a circuit defined by the vehicle's cooling system. U0623 sets when a control module stops receiving expected messages from pump A, so it cannot confirm or command that pump's operation normally.
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
- Cooling system may not operate as intended
How to diagnose it
- Scan all modules for communication codes and save freeze-frame data to identify whether pump A went offline with a low-voltage or broader network fault.
- Check the temperature gauge and live coolant temperature, and look for a pump A status or command value if the scan tool provides one.
- With the engine cool, inspect pump A's connector and wiring for damage, coolant contamination, corrosion, or loose terminals.
- Check the pump module's fuse, power, and ground using the manufacturer's wiring diagram.
- Test the network wiring to pump A for opens and shorts according to the manufacturer's procedure.
- If power, ground, and network wiring pass, verify pump A's communication and operation before replacing it.
Common fixes
- Repair damaged or corroded pump A wiring and connector terminals.
- Replace a failed fuse or restore pump A's power or ground.
- Repair an open or short in the pump A network circuit.
- Replace coolant pump A if its supply and network wiring are sound but it does not communicate or operate.
Can I keep driving?
Do not continue driving if the temperature gauge rises, a temperature warning appears, or coolant circulation seems impaired; stop safely and let the engine cool. Pump A may serve a cooling circuit needed to prevent overheating, which can quickly cause engine damage.
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.