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P0480 and P0481: cooling fan relay control circuit
A cooling fan that does not run produces a very specific pattern: fine on the motorway, overheating in traffic. That pattern is the diagnosis.
At motorway speed, air flows through the radiator whether or not the fan runs. In traffic, nothing moves that air except the fan.
That produces the single most diagnostic symptom in the cooling system: temperature normal at speed, climbing in traffic. If that is your complaint, start with the fan.
| Code | Meaning |
|---|---|
| P0480 | Cooling fan 1 control circuit |
| P0481 | Cooling fan 2 control circuit |
| P0482 | Cooling fan 3 control circuit |
Related: radiator fan not working and P0691 and P0692 fan control circuit.
Two fan architectures
Which one you have determines what can fail.
Relay-switched fans run at one or two fixed speeds, switched by relays. Simple, and the relay is the usual failure. Often two relays: one for low speed, one for high.
Variable speed fans use a control module that varies speed continuously with a PWM signal. Quieter and more efficient, and the failure modes are electronic rather than mechanical.
A vehicle with a variable speed fan will not respond to the relay-swap test below, because there is no relay to swap.
The checks, in order
1. Does the fan run at all?
Turn on the air conditioning with the engine idling. On almost every vehicle, this commands the fan immediately regardless of coolant temperature.
| Result | Meaning |
|---|---|
| Fan runs with A/C on | Fan and its power path work |
| Fan silent with A/C on | Power, relay, motor or fuse |
| Fan runs constantly, never stops | Relay stuck closed, or temperature sensor reading hot |
That single test splits the diagnosis in half in ten seconds.
2. Fuses
Cooling fans draw substantial current and usually have a high-rated fuse of their own, often in the engine bay box rather than the cabin. Test with a meter — a fuse can look intact and be open: fuses and relays basics for owners.
3. The relay
Swap it with an identical relay from a non-critical circuit. If the fault follows the relay, done.
4. The temperature signal
The ECU commands the fan based on coolant temperature. A sensor reading cold means the ECU never asks for the fan, and the fan itself is perfectly healthy.
Check that the live coolant temperature is plausible: P0116 to P0119 coolant sensor performance.
5. The motor
Fan motors seize, and brushes wear out. A motor drawing excessive current will also burn relay contacts, which is why a repeatedly failing relay points at the motor.
6. Wiring and ground
The fan ground is often on the body or the radiator support, in a place that corrodes.
The constant-running version
A fan that runs all the time, from cold start until you park, is the opposite fault and often more alarming to owners because it is audible.
Causes:
- Relay stuck closed — the contacts welded together.
- Coolant temperature sensor reading hot, so the ECU asks for the fan constantly.
- The ECU commanding it as a failsafe, which some vehicles do when the temperature signal is implausible.
It also drains the battery when the fan continues after switch-off: parasitic battery drain diagnostics.
Do not just watch the gauge
Dashboard temperature gauges are heavily damped and deliberately sit in the middle across a wide range of real temperatures. By the time the needle moves, the situation is already significant.
Log actual coolant temperature and watch when the fan cuts in. A healthy system shows a clear plateau or a slight fall as the fan engages.
Temperature gauge fluctuating and engine overheating diagnosis.
Why it matters more than it sounds
An engine that overheats does real damage: warped heads, failed gaskets, and sometimes a replacement engine. The code that records it afterwards is P0217 engine over-temperature.
A fan relay is one of the cheapest parts on the car. The consequence of ignoring it is not.
Sequence
- Test with the air conditioning on — the fastest split.
- Check the fuse with a meter.
- Swap the relay with an identical one.
- Verify coolant temperature is being read correctly.
- Check the ground connection.
- Test the motor by powering it directly.
- Log a drive in traffic afterwards to confirm the fan engages.
This check needs no workshop — an ELM327 adapter and the free tier of the app cover it. Log coolant temperature while stationary with the engine idling. Watching the moment the fan engages, and whether temperature responds, is the whole test.
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