TORQDEX // COOLING SYSTEM DIAGNOSTIC
Radiator Fan Not Working
Diagnose an electric radiator fan that does not operate by checking fan command, fuses, relays, power supply, ground, control modules, temperature inputs, and fan-motor condition.
01 // WHAT IT MEANS
Understanding the symptom
Electric radiator fans may be controlled by relays, resistor networks, solid-state modules, or direct computer commands depending on the vehicle.
A fan that does not run should be diagnosed by separating the control side of the circuit from the high-current motor circuit.
02 // QUICK CHECKS
Check these first
Start with simple observations and scan data before moving into deeper testing.
Check whether the fan is being commanded
Use scan data or an active test when available to determine whether the controller is requesting fan operation.
Check fan fuses
Inspect high-current and control-circuit fuses for open circuits or signs of overheating.
Try A/C operation
On many vehicles, air-conditioning operation can command one or more cooling fans.
Inspect the fan connector
Look for melted terminals, corrosion, loose pins, or damaged wiring near the fan motor.
03 // SYSTEMS TO CHECK
Common systems involved
Fan motor
Internal motor wear, seized bearings, brush failure, or open windings can prevent fan operation.
High-current power circuit
Fuses, relays, wiring, and connections must carry substantial current to the fan motor.
Fan ground circuit
A poor ground can prevent fan operation even when power is present.
Fan command and temperature input
Temperature sensors, pressure sensors, modules, relays, and communication faults can prevent the fan from being commanded.
04 // DIAGNOSTIC ORDER
Diagnose it in this order
Verify coolant-temperature data
Confirm the controller is seeing plausible engine temperature.
Command the fan if possible
Use a scan-tool output test to separate control logic from motor and power-circuit faults.
Check power and ground at the fan
Measure voltage and ground quality while the fan is commanded on.
Check relays and fuses
Verify relay control, relay output, high-current protection, and terminal condition.
Perform voltage-drop testing
Measure voltage loss across the fan power and ground circuits under load.
Evaluate the motor or fan module
If correct power, ground, and command are present but the fan does not operate, test the motor or integrated control module.
05 // TEST RESULTS
What the results may indicate
Check relay, fuse, and power circuit
The control system is requesting fan operation, but the high-current path is not delivering power.
Fan motor or module is suspect
If proper voltage and ground reach the fan while commanded, internal fan failure becomes likely.
Check inputs and control logic
Verify temperature inputs, A/C pressure data, module communication, wiring, and control strategy.
06 // COMMON MISTAKE
Don't replace the fan motor before checking whether it is actually being commanded
A failed sensor, relay, control module, fuse, or wiring fault can keep a good fan motor from operating. Verify command, power, and ground before replacing the fan.
07 // RELATED OBD-II CODES
Related trouble codes
08 // RELATED TORQDEX TOOLS