2001 E46 318ci - aux fan always on!

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  1. 2001 E46 318ci - aux fan always on! (FIXED) 
    #1
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    Hey guys I've got an aux fan problem. About 10-15 seconds after I start the car the aux fan comes on builds up to a high speed and stays on constantly throughout my journey. When I turn the car off it stops straight away. I've a feeling I may have a faulty sensor/ switch somewhere but what checking of switches/sensors can I do at home and where are they located so I can narrow the fault down. I'd rather spend a few pound on a sensor and fit it myself than take it to a garage. I got the car from an independent dealer and the car is still under warranty with him but his mechanic doesn't seem to think there is anything wrong so I'm not keen on taking it back there yet until I can identify the problem. In fact they fitted a new hedgehog last week for my wonky climate control and he said the aux fan was linked to that which I know it isn't, so my faith in him isn't great. If it's a cheap, easy fix I'll just do it myself. Any help guys would be greatly appreciated.
    Last edited by CRIBBYRHYMES; 29-09-2009 at 23:40. Reason: Title change - problem solved
     
     

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    First thing I'd advise would be getting the BMW fault codes read for the cars engine ECU and heater ECU, any Main dealer(more expensive), BMW Independent specialist or good independent garage should be able to do this for you, get a copy of any codes and then post them up here and we will help out where we can with what you need to do next.

    Would also be worth checking the high speed fan relay and low speed relay. I think they are behind the glovebox. I'll check for you.
     
     

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    CRIBBYRHYMES (29-08-2009)

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    Thanks Ronnie
    Went this morning to a recommended Independent garage and he checked the codes for me free of charge. My emissions light came on yesterday aswell and it threw up an o2 sensor fault on the machine so hes going to replace that. No other codes were showing though, he thinks it might be the coolant temperature sensor which he will check when replacng the o2 sensor but surely that would have shown up a fault code? Didnt realise there were replaceable relays for the fan speeds so a hows to in how to check these would be much appreciated.
     
     

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    Quote Originally Posted by CRIBBYRHYMES View Post
    Thanks Ronnie
    Went this morning to a recommended Independent garage and he checked the codes for me free of charge. My emissions light came on yesterday aswell and it threw up an o2 sensor fault on the machine so hes going to replace that. No other codes were showing though, he thinks it might be the coolant temperature sensor which he will check when replacng the o2 sensor but surely that would have shown up a fault code? Didnt realise there were replaceable relays for the fan speeds so a hows to in how to check these would be much appreciated.
    The coolant temp sensor won't flag up a fault code unless it breaks.

    As there's only one sensor that tells the ECU what the coolant temp is there's no way the ECU knows if the water is 50.C like the sensor is saying or 90.C like it could actually be.
     
     

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    OK, new o2 sensor has been fitted and the emissions light has stayed off. He couldnt find any fault with the coolant temperature sensor and the diagnostic didnt reveal any issues either. Suspected fault with the module integrated into the fan but even then he wasnt 100% sure as it cut out the minute the engine stopped and he had seen it before but the fan stayed on after ignition was cut. Went back to the dealer I got the car from today and they fitted a brand new BMW OEM fan and guess what......it made no difference whatsoever. About 10 seconds after startup it takes off like a jet plane and stays on for the whole journey. At least I got a brand new fan for nothing any clues guys as to what else might be at fault? Could there be problems with the ECU? Other than this issue the car runs like a dream no other problems.
     
     

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    Got the car hooked up to the GT1 today for a full diagnostic. It was showing an air conditioner fault. Fan and relay system all ok as is wiring loom for fan and relays. It needs a new air conditioning condenser unit and he said the wiring and plug to this should also be checked as this would show the same symptoms, so best to check before putting in the new unit. He also cleared a dormant air bag activation fault from the time of the cars crash in 2005, but said that their is a chance that the condenser or its wiring could have been damaged at the time of the crash but as the fan running all the time wont cause any more issues other than being hard on the battery and wearing the fan out prematurely the previous owner never got it sorted. So back to the dealer it goes armed with this new info to get it fixed under warranty. Fingers crossed it finally sorts it.
     
     

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    Ok guys, been fiddling around with a few things waiting around for the car going in on 22nd. when I pull fuses 62 and 63 the fan doesn't come on, so I think the problem is definitely linked to the air con in some way. Anybody have any idea what sensors, plugs or wires I can check that are linked to the air con, condenser?
     
     

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    Starting to feel a bit lonely here guys, either nobody knows or nobody cares........
     
     

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    This is what I have on the E46:

    The fan speed is influenced by the coolant temperature at the radiator outlet and the pressure in the air conditioning system. The fan speed is reduced as the vehicle speed increases.

    The electric fan is driven at maximum speed in the event of a fault in the coolant temperature sensor at the radiator outlet.

    I haven't had any experience of this myself but it may be some help.
     
     

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  14. 2001 E46 318ci - aux fan always on! (FIXED) 
    #10
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    Got the car back tonight 100% working, happy days!
    They tried re-gassing the air con to no avail, the compressor wasnt kicking in at all, so they set about checking wiring looms and plugs for any broken connections. Im not sure where exactly it was but after hours of testing wires they came across a set of broken wires and a plug. A new plug was put on and everything connected back up and hey presto everything is working 100%. Air con is kicking in and working great and the cooling fan is only coming on when it should instead of running at full speed all the time. Fingers crossed the problem is finally sorted in the long term.
     
     

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