What it means
Module cooling fan control voltage below expected range. A communication loss with this module breaks any function relying on its data — diagnostic tools may show 'no response' and dependent modules can fall into limp mode.
At a glance
- Usually lights the warning light of the system that lost communication
How it works
The control module cooling fan removes heat from a high-load module, and its control circuit lets the module command or monitor fan operation. U350D indicates the circuit signal is lower than the module expects, commonly because the wire is shorted to ground; a gateway or network fault can also affect reported status.
Common causes
Most likely first.
- Wiring shorted to ground
- Gateway module routing CAN messages incorrectly
- CAN terminating resistor (120 Ω) drifted out of spec
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
- Record freeze-frame data and scan all modules for related fan, low-voltage, and communication codes to see whether the fault is local or network-wide.
- Identify the fan circuit and inspect its wiring and connectors for chafing, crushed insulation, corrosion, or contact with ground.
- Command the cooling fan on with a scan tool under the manufacturer's specified test conditions and note whether it runs or the circuit reading changes.
- Test the circuit for a short to ground and check its power and ground feeds against the manufacturer's specification.
- If wiring tests pass, investigate gateway routing and network faults, then verify the module's fan output using vehicle-specific service information.
Common fixes
- Repair chafed or pinched fan-control wiring that is shorted to ground.
- Clean and secure corroded or loose fan-circuit connections.
- Repair a faulty fan power or ground feed.
- Repair a confirmed gateway or module control fault after circuit testing.
Can I keep driving?
If the module is overheating, shutting down, or limiting vehicle functions, stop driving when safe because continued use can lead to module shutdown or damage. If the vehicle behaves normally and shows no temperature warning, keep trips short and monitor for changes.
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.