What it means
A control module has stopped receiving expected network messages from fan 2. The effect on cooling depends on the vehicle's fan and control-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
Fan 2 is the second cooling fan named by the vehicle's control system, and its operating status is exchanged with other modules over the network. U0633 sets when expected messages from fan 2 are missing, which is distinct from a fan 1 communication fault and does not alone prove fan 2 has failed.
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 fan may not operate as intended
How to diagnose it
- Record freeze-frame data and scan all modules for fan 2, cooling, network, and electrical supply codes.
- Use live data to check fan 2's reported status or command and compare its response with fan 1 where the system permits.
- Inspect fan 2's harness, connectors, and nearby routing for chafing, corrosion, loose pins, or heat damage.
- Check power and ground at the fan 2 controller using the wiring diagram and manufacturer's specifications.
- Test fan 2's network wiring for opens and shorts using the manufacturer's method, then assess its controller if the circuit and supplies are good.
Common fixes
- Repair damaged or shorted wiring on fan 2's communication path.
- Clean or replace corroded or loose terminals at fan 2's connector.
- Repair a poor power or ground connection to the fan 2 controller.
- Replace the fan 2 controller only after its wiring and power and ground checks pass.
Can I keep driving?
If fan 2 contributes to cooling, avoid traffic, prolonged idling, and heavy loads until the cooling system's operation is confirmed. Stop if engine temperature rises or a warning appears, since reduced fan capacity can cause overheating.
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.