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DTC codes / U35xx · Network communication / U350C

U350CControl Module Cooling Fan Circuit/Open

U350C is a generic network code indicating that a control module has detected an open circuit in the cooling fan control circuit, meaning the expected electrical path is broken or has excessive resistance. The module monitors the fan circuit and sets this code when the commanded fan operation does not match the feedback signal, often due to a wiring fault, failed fan motor, or faulty control module.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaNetwork communication

Symptoms you may notice

  • Cooling fan does not run at all, leading to engine overheating in traffic or at idle
  • Fan runs continuously at full speed regardless of engine temperature
  • Air conditioning performance degrades because the condenser fan is not operating
  • Intermittent fan operation that may cause temperature gauge fluctuations
  • Often no symptoms besides the warning light if the fault is in the feedback circuit only
  • Engine may enter reduced power mode or set additional overheating-related codes

Common causes, most likely first

  1. Broken, corroded, or disconnected wiring in the cooling fan circuit
  2. Failed cooling fan motor or fan assembly
  3. Defective cooling fan relay or control module
  4. Poor ground connection at the fan motor or chassis
  5. Faulty coolant temperature sensor or fan switch sending incorrect signals
  6. Open fuse or fusible link in the fan power circuit
  7. Internal fault in the control module that monitors the fan circuit

How to diagnose and fix it

  1. Inspect the cooling fan fuse and relay, replacing any blown fuse or faulty relay
  2. Check the fan connector and wiring for damage, corrosion, or loose pins
  3. Test the fan motor by applying power directly to verify operation
  4. Measure resistance and voltage drop across the fan circuit to locate an open
  5. Verify ground connections at the fan motor and chassis are clean and tight
  6. Scan all modules for related codes and check live data for fan command and feedback
  7. If all external circuits test good, diagnose or replace the control module as needed

Why the fan circuit open code misleads

  • A fan that spins freely by hand can still have an open internal circuit that only fails under heat or load, so a visual check is not enough.
  • The code can be set by a faulty coolant temperature sensor even when the fan motor and wiring are perfect, because the module never commands the fan on.
  • Some vehicles use a pulse-width modulated fan controller that can fail intermittently, setting U350C without ever storing a fan-related code in the engine module.
  • Aftermarket alarm or remote start installations often tap into the fan circuit and create opens that mimic a failed fan motor.
  • A weak battery or charging system fault can cause modules to misreport fan circuit status, so always check system voltage first.

Can I keep driving with U350C?

If the engine temperature gauge stays in the normal range and the fan runs at least sometimes, you can drive short distances to a repair shop, but avoid heavy traffic and long idles. If the temperature climbs above normal or the warning light flashes, pull over and stop the engine to prevent overheating damage.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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