Thursday, November 29, 2012

"Radiator fan" "Engine Fan" "COOLING FAN WILL NOT TURN OFF"

Ignition OFF but Radiator Cooling Fan won't turn OFF

As we know that if the cooling fan is not turning ON,then we notice Engine Overheating issues

But here the case is reverse,the Engine Cooling fan is not turning OFF.

So to troubleshot the issue,we have to go to the basics.

First know what electrical components are controlling the fan or what components are operating the fan and making it run.

The first thing is Cooling Fan relay,next is cooling fan switch and another is cooling fan fuse.
On some car models there is no fuse for cooling fan.

On some now days latest car there is module which controls cooling fan.These module is called cooling fan module.

The fan relay open and closes and fan gets command to start and stop.
The most first and very common problem for fan not turning off is faulty relay.Because if fan control fuse is faulty then fan will not turn on at all.

But here fan is running,so it can be shorted relay connections or relay itself.If relay gets bypassed,the fan will get direct power and these will make it run non stop.

In the vehicle there are few electrical components on dashboard which always operate even when ignition is off.If in case the fan relay wiring gets connected to these Always On component wiring then Fan will remain always on.

So first thing to check is fan relay and next is Fan relay wiring and fan wiring.Check for 12 volts to these wiring.Check voltage both in ignition off and ignition ON.If the fan is getting voltage with ignition off,then its definitely the issue of fan wiring short.

Now one more thing,if the relay and wiring checked ok,then another thing is fan switch.

On some models there is thermoswitch beside the radiator. These switch gets faulty or short and due to these also fan will not turn off.

When the coolant fan thermoswitch goes bad it defaults to the closed run all the time position, which is better then the open never run overheat until head gasket blows position.

On some models the very rare problem occurs.
You check the relay,its ok,you check cooling fan switch its ok,you check its wiring its ok,you check the fuse its ok,the fan will not turn off.
One such case came at our Auto repair garage.

The problem was very strange when we traced the fault.

The fuse slot where cooling fan fuse was fitted,under that fuse slot,the arch/spark occurred sometime back and that area got burned and that got shorted.So when e checked fuse it was not blown,it was working fuse.
The problem is the pins that hold the fuse are small and will/can arch and burn that area of the fuse block without blowing that fuse causing an area of high electrical resistance .
So in testing it showed us 12 volts on one side and like 6.5 volts on the other side of the fuse.And these tells FCM (fan control module) to enter sleep mode and make a/c compressor not work and cooling fans to not operate at all.Or work non stop.
But when we checked voltage it made all clear that issue is there in the area of fuse slot.

So always remove the fuse from its position,visually inspect both fuse as well as its area of placement.

These details will help.

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It can be faulty fan relay. The relay is not turning the system off. Or its wire short issue. Even with ignition off, the fan relay is getting power so it’s not letting the fan to turn off. Bypass the fan control relay and see if still the fan works with ignition off or not.

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