Stuck Cooling Fan Relay
Stuck Cooling Fan Relay means the fan relay is stuck closed and keeps the fan running after it should shut off It can cause overheating, fan warnings, AC performance problems, or intermittent fan operation depending on the vehicle.
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Most Likely Causes
- 1
Failed fan motor, relay, fuse, or control module
The fan circuit may have a bad motor, stuck relay, blown fuse, or failed solid-state control module.
- 2
Bad coolant temperature or AC pressure input
Fan command often depends on coolant temperature and AC pressure. A bad sensor input can keep the fan off, on, or cycling incorrectly.
- 3
Loose connector, corroded terminal, or damaged wiring
Heat, vibration, road splash, and previous repairs can damage fan wiring and connector terminals.
- 4
Mechanical restriction or debris
Debris, shroud damage, or a seized fan can overload the motor or keep the fan from spinning.
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How to Diagnose It
- 1
Command the fan on with a scan tool if supported
Use bi-directional control to see whether the fan responds when commanded independently of engine temperature.
Tool: Bi-directional scan tool
- 2
Check fan fuse, relay, power, and ground
Verify power and ground at the fan or control module while the fan is commanded on.
Tool: Multimeter or test light
- 3
Monitor coolant temperature and AC pressure data
Compare live data to actual engine temperature and AC operation to see whether the computer should be commanding the fan.
Tool: Scan tool
- 4
Inspect fan blades, shroud, connector, and harness
Look for debris, melted connectors, loose pins, corrosion, rubbed wires, or damaged fan blades.
Tool: Flashlight
How to Fix It
Repair confirmed electrical fault
Replace the bad fuse, relay, connector, wiring section, or control module after testing the circuit.
Replace failed fan motor or assembly
If power and ground are present but the fan does not run or runs weakly, replace the fan motor or fan assembly.
Correct sensor or cooling-system input problems
Repair coolant temperature sensor, AC pressure sensor, thermostat, low coolant, or overheating causes that are commanding fan operation incorrectly.
Parts & Tools
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Related Issues
Bad Cooling Fan Relay
A bad cooling fan relay can stop the radiator fan from turning on when the engine gets hot. This can cause overheating at idle, overheating in traffic, weak AC performance at low speeds, or a cooling fan that only works sometimes. The relay should be tested before replacing the fan motor because a fan motor can look dead when the relay is not sending power.
Blown Cooling Fan Fuse
Blown Cooling Fan Fuse means the fuse protecting the radiator fan circuit has opened, usually because the fan circuit drew too much current or shorted The repair should start with power, ground, fuse, connector, and load testing instead of guessing at modules or replacing parts at random.
Cooling Fan Relay Failure
Cooling Fan Relay Failure means the relay that supplies fan power is stuck open, stuck closed, or intermittently failing It can cause overheating, fan warnings, AC performance problems, or intermittent fan operation depending on the vehicle.
Other Cooling Issues
Browse more diagnostic guides in this category.
AC Compressor
Your ac compressor is the heart of your air conditioning system, pressurizing refrigerant to cool cabin air. A failing compressor will leave you blowing hot air and typically requires replacement rather than repair.
AC Compressor Car
An ac compressor car component is the heart of your air conditioning system, pumping refrigerant to cool cabin air. When it fails, your AC stops working entirely, leaving you in uncomfortable heat.
AC Compressor Cost
AC compressor cost typically ranges from $500 to $1,500 at a repair shop, including parts and labor, with DIY replacements costing $100–$400 in parts alone. A failing compressor reduces cooling performance and can damage other AC components if left unaddressed.
AC Compressor Oil
AC compressor oil is a specialized lubricant that reduces friction inside your compressor and keeps it running efficiently. Low or contaminated compressor oil can damage your AC system and lead to expensive repairs.
AC Compressor Price
AC compressor price varies widely based on your vehicle make and model, with costs typically ranging from $200 to $1,500 or more for parts alone. Professional installation adds labor charges, making total replacement costs significantly higher—often $500–$2,500 at a shop.
AC Compressor Pulley
The ac compressor pulley is a spinning component that engages and disengages the compressor from the serpentine belt to control when your air conditioning runs. When it fails, your AC won't work properly and you'll hear grinding or squealing noises from the engine bay.
Mistakes to Avoid
- Do not replace the radiator fan before checking fuses, relays, power, and ground.
- Do not ignore fan problems on a vehicle that overheats at idle or in traffic.
- Do not jump fan wires without using proper fused test leads.