Cooling Fan Not Operating
Diagnostic path for radiator fan no-operation, overheating at idle, A/C warm at idle, relays, fuses, fan command, and motor checks.
A cooling fan fault should be split into command, power, ground, relay/fuse, motor, sensor input, and airflow problems. Do not replace the fan assembly until command and circuit behavior are confirmed.
Common Sounds or Signs
- Overheats in traffic but cools while driving
- A/C gets warm at idle
- Fan never comes on or only one fan operates
- Fan runs constantly after shutdown
Quick Checks
- Verify coolant level and actual engine temperature before electrical testing
- Command the fan with a scan tool when supported
- Check fan fuses, relays, control module, power feed, and ground under load
- Check ECT data plausibility and A/C pressure request inputs
- Backprobe motor current draw or voltage drop before condemning the fan assembly
Inspection Priority
- Verify coolant level and condition first.
- Inspect thermostat behavior and circulation evidence together.
- Pressure test the cooling system when coolant loss or smell is present.
Common Causes
- Failed fan motor or high-resistance fan connector
- Blown fuse, failed relay, control module, or missing power feed
- Poor ground or voltage drop in fan circuit
- ECT sensor data, A/C pressure input, or PCM command issue
- Blocked condenser/radiator airflow or damaged fan shroud
Diagnostic Path
Pick the first inspection path.
Command Path
Find whether the PCM is requesting fan operation and why.
- Compare actual temperature to scan-tool ECT
- Check fan command with A/C request
- Review P0117, P0118, P0480, and pressure sensor data
Power and Motor Path
If command exists, prove fuse, relay, feed, ground, and motor behavior under load.
- Load test fan power and ground
- Check relay control and fuse voltage
- Measure motor current draw if accessible
Next Best Step
Inspect before expanding the quote.
Pressure test cooling system
Confirm external leaks, cap behavior, and pressure loss before parts.
Inspect thermostat
Compare warm-up, scan temperature, and hose temperature behavior.
Verify radiator fan operation
Check fan command, AC-load response, fuses, relays, and airflow.
Related Inspection
Recommended Next Repair Paths
Compare repair paths before replacing parts.
Radiator Fan Replacement
Use after command, fuse, relay, power, and ground checks confirm the fan motor or assembly.
Cooling Fan Diagnosis
Use when command or circuit testing is needed before parts are selected.
Explore Related Systems
Use when multiple systems overlap.