What it means
The vehicle bus reports loss of communication with smart cooling fan 4 (PWM brushless fan with own controller). Fan speed cannot be commanded; cooling falls back to default operation.
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
Cooling fan 4 is a brushless fan with its own controller, and the vehicle network carries its speed commands. U067D sets when communication with fan 4 is lost, preventing reliable speed control and potentially reducing cooling if the fallback strategy is insufficient.
Common causes
Most likely first.
- Bus wiring open or shorted
- Module without power or ground
- 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
- Scan all modules for communication codes and save freeze-frame data, then review coolant temperature and available fan status data.
- With the engine cool, inspect fan 4's connector and harness for corrosion, loose pins, heat damage, or chafing.
- Use vehicle service information to locate fan 4, then check its fuse, power, and ground against the manufacturer's specification.
- If supported, command fan 4 with a scan tool and see whether it responds while other fans operate.
- Test fan 4's network wiring for opens or shorts according to the manufacturer's procedure.
- If the wiring and supplies are good, use the manufacturer's diagnostic process to confirm a failed fan 4 controller or assembly.
Common fixes
- Reconnect fan 4 and repair damaged connector or harness wiring.
- Replace a failed fuse or repair fan 4's power or ground connection after finding the cause.
- Repair an open or short in the network wiring to fan 4.
- Replace the confirmed failed fan 4 controller or fan assembly.
Can I keep driving?
Avoid prolonged idling, towing, and high-load driving until fan 4 is operating, and keep an eye on coolant temperature because insufficient cooling can overheat the engine. Stop and shut the engine off if the temperature enters the danger range.
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.