Symptom
Cooling fans running constantly or not at all
Fans that run whenever the engine is on, or never run when they should. Constant running with a normal temperature gauge usually means a sensor reporting a false high rather than genuine overheating.
Also described as: fans always on, fan running constantly, fans not working, cooling fan always on, fan won't turn off, radiator fan issue, فن دائم کار میکند, فن رادیاتور کار نمیکند, ventilador siempre encendido, electroventilador no para, ventilador no arranca nunca, ventilador no para, مروحة التبريد شغالة على طول, المروحة شغالة دايما, مروحة الرادياتير لا تتوقف, المروحة تشتغل باستمرار, المروحة ما تدور أبدا
Some causes mean you should stop driving
1 of the 46 codes that produce this symptom indicate a fault where continuing to drive risks damage or is unsafe. If the symptom is sudden or severe, treat it as one of those until a scan says otherwise.
What this usually means
The two halves of this complaint are opposite faults and they want opposite diagnoses, so establish which is happening before anything else.
Fans that never run turn an ordinary traffic queue into an overheat while motorway driving stays perfectly normal — airflow at speed hides the fault entirely. That pattern is itself diagnostic, and it is the more urgent half because the consequence is engine damage.
Fans that run constantly with a normal temperature gauge usually mean a sensor reporting a false high rather than genuine overheating. The control module acts on what it is told, so a temperature signal biased high, or a circuit shorted, produces full-speed fans on a cold engine. The fans are the symptom rather than the fault, and renewing them changes nothing.
But constant running is not always a fault at all. Air conditioning requests the fans whenever the compressor runs, so a car with climate control set to automatic runs its fans far more than an owner expects. Switch the air conditioning off and see — that free test separates a request from a fault.
When fans genuinely will not run, the population is short and testable in order: the fuse, the relay or control module, the fan motor itself, and the temperature signal that requests them. Command the fans on a scan tool; a fan that runs on command but never on its own is a request problem, and one that will not run on command is a supply or motor problem.
And a fan that runs at one speed only is usually its resistor pack or control module, which is a common and inexpensive failure.
Working through it
| What you find | Likely cause | How to confirm it | What fixes it |
|---|---|---|---|
| Overheats in traffic, normal at speed | Fans not running — airflow at speed masks it completely | Watch the fans with the engine hot and again with the air conditioning on. Command them on a scan tool if they do not start. | Repair the fuse, relay, module or motor the tests name. Treat as urgent — this is the half that damages engines. |
| Fans run at full speed from cold start, gauge normal | A temperature signal reading falsely high, or a circuit shorted — the module acts on what it is told | Compare live coolant temperature against an infrared measurement of the housing. Implausibility with a cold engine is the finding. | Renew the sensor or repair the circuit. The fans are correct; the information is not. |
| Fans run whenever the climate system is on | Not a fault — the air conditioning requests them whenever the compressor runs | Switch the air conditioning off, including automatic climate modes, and see whether they stop. Free and immediate. | No repair. Explain rather than diagnose. |
| Runs on command but never by itself | The request rather than the fan — the module is not asking | Command on a scan tool; a fan that responds proves supply and motor. Then check the requesting signal and the module's coding. | Repair the temperature signal or the module. Do not fit a fan that has just proved it works. |
| One speed only, or high speed only | The resistor pack or the fan control module — a common and inexpensive failure | Command each speed in turn. A missing intermediate speed names the resistor or module rather than the motor. | Renew the resistor pack or control module. Check its connector, which runs hot and often melts. |
| Fans run on after the engine is switched off | Normal on many vehicles — run-on cooling after a hard drive, and standard on turbocharged engines | Note whether it stops by itself within some minutes. Self-limiting behaviour is the design. | No repair. A fan that never stops and flattens the battery is a relay stuck closed, which is a different fault. |
-
Overheats in traffic, normal at speed
- Likely cause
- Fans not running — airflow at speed masks it completely
- How to confirm it
- Watch the fans with the engine hot and again with the air conditioning on. Command them on a scan tool if they do not start.
- What fixes it
- Repair the fuse, relay, module or motor the tests name. Treat as urgent — this is the half that damages engines.
-
Fans run at full speed from cold start, gauge normal
- Likely cause
- A temperature signal reading falsely high, or a circuit shorted — the module acts on what it is told
- How to confirm it
- Compare live coolant temperature against an infrared measurement of the housing. Implausibility with a cold engine is the finding.
- What fixes it
- Renew the sensor or repair the circuit. The fans are correct; the information is not.
-
Fans run whenever the climate system is on
- Likely cause
- Not a fault — the air conditioning requests them whenever the compressor runs
- How to confirm it
- Switch the air conditioning off, including automatic climate modes, and see whether they stop. Free and immediate.
- What fixes it
- No repair. Explain rather than diagnose.
-
Runs on command but never by itself
- Likely cause
- The request rather than the fan — the module is not asking
- How to confirm it
- Command on a scan tool; a fan that responds proves supply and motor. Then check the requesting signal and the module's coding.
- What fixes it
- Repair the temperature signal or the module. Do not fit a fan that has just proved it works.
-
One speed only, or high speed only
- Likely cause
- The resistor pack or the fan control module — a common and inexpensive failure
- How to confirm it
- Command each speed in turn. A missing intermediate speed names the resistor or module rather than the motor.
- What fixes it
- Renew the resistor pack or control module. Check its connector, which runs hot and often melts.
-
Fans run on after the engine is switched off
- Likely cause
- Normal on many vehicles — run-on cooling after a hard drive, and standard on turbocharged engines
- How to confirm it
- Note whether it stops by itself within some minutes. Self-limiting behaviour is the design.
- What fixes it
- No repair. A fan that never stops and flattens the battery is a relay stuck closed, which is a different fault.
Codes that produce this symptom (46)
Listed with the codes that most typically present this way first — the likeliest place to start.
- P0115 Engine Coolant Temperature Sensor 1 Circuit Typical of this code High
- P0117 Engine Coolant Temperature Sensor 1 Circuit Low Typical of this code High
- P0480 Cooling Fan 1 Control Circuit Typical of this code High
- P0481 Cooling Fan 2 Control Circuit Typical of this code Moderate
- P0482 Cooling Fan 3 Control Circuit Typical of this code Moderate
- P0483 Cooling Fan Rationality Check Typical of this code High
- P0484 Fan Circuit Current High Typical of this code Moderate
- P0485 Cooling Fan Power/Ground Circuit Typical of this code High
- P0493 Cooling Fan Overspeed Typical of this code Moderate
- P0495 Fan 1 Overspeed Typical of this code Low
- P0526 Fan Speed Sensor Circuit Typical of this code Moderate
- P0527 Fan Speed Sensor Circuit Range/Performance Typical of this code Moderate
- P0528 Fan Speed Sensor Circuit No Signal Typical of this code Moderate
- P0529 Fan Speed Sensor Circuit Intermittent Typical of this code Moderate
- P0691 Cooling Fan 1 Control Circuit Low Typical of this code High
- P0692 Cooling Fan 1 Control Circuit High Typical of this code High
- P0693 Cooling Fan 2 Control Circuit Low Typical of this code Moderate
- P0694 Cooling Fan 2 Control Circuit High Typical of this code Moderate
- P0695 Cooling Fan 3 Control Circuit Low Typical of this code Moderate
- P0696 Cooling Fan 3 Control Circuit High Typical of this code Moderate
- P2184 Engine Coolant Temperature Sensor 2 Circuit Low Typical of this code Moderate
- P2B2F Fan 1 Performance/Stuck Off Typical of this code High
- P00B2 Radiator Coolant Temperature Sensor Circuit Range/Performance Moderate
- P0118 Engine Coolant Temperature Sensor 1 Circuit High High
- P0119 Engine Coolant Temperature Sensor 1 Circuit Intermittent/Erratic Moderate
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
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- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
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