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PaulHodg

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About PaulHodg

  • Rank
    Newbie

Contact Methods

  • First Name
    Paul

Profile Information

  • Ford Model
    S Max
  • Ford Year
    2008
  • UK/Ireland Location
    Hertfordshire
  1. Like a lot of people it seems, I had trouble with the radiator/cooling fan not operating on my S Max. Presumably this also applies to the Galaxy mk3 and the Mondeo. I have now fixed the problem and thought it would be helpful to share what I know as there is little information that I found when searching the internet, some of which is incorrect. I am an electronics/software engineer by trade and so for my own curiosity as much as anything I wanted to find out how the fan operates..... Attached to the cooling fan housing is a speed controller in a small metal box. Some forum posts refer to this as a relay box, which is incorrect. It is driven by a PWM signal - to those who don't know what that is, it is a continuous series of pulses that change width dependant on the speed required. There are three wires going to the fan controller, a permanent 12V feed (Red), a ground (Black) and a pink wire. The pink wire is the control (PWM) wire. There are two wires that come out of the other end of the speed controller and connect to the fan. The powertrain control module (PCM) in the wheel arch drives the PWM signal on the pink wire. So how do you tell if the fan should be on? The signal on the pink wire appears to be an open-collector drive - a bit technical but basically means that you probably won’t be able to measure a signal unless it is plugged in to the fan speed controller at the time. This is also how the PCM detects a fan fault. The speed controller has an internal pull-up resistor between the pink wire and 12V (Measures about 2700 ohms). When the fan is connected, the PCM module can see the 12V on the pink wire, so when the fan is disconnected, the 12V disappears from the pink wire and the PCM can detect a fault. If you have a voltmeter - when connected between ground and the pink wire you should see 12V (or whatever the battery voltage is) when the fan is off and a lower voltage when the fan is on. The actual voltage will depend on how fast the fan should be going and the type of voltmeter but it will probably be around 4V at full speed. I believe there are two ways to force the fan to come on. The first is to disconnect the engine temperature sensor - however I did not try this as I was not sure where it was. The second method (that I used) is to turn the aircon on full - when the aircon is on the cooling fan should come on full speed. This will only happen though when the engine is running as the aircon pump has to be engaged. If you just want to test the fan itself works, you can disconnect the 2 pin connector from the output of the fan controller and connect them to 12V and GND. I did this by also removing the 3 pin connector and using the red and black connections on their to link across to the fan connector. So what was wrong with my fan ? I had what appears to be a common problem of the pink control wire being broken/corroded in the wiring loom. The following is a description of a right hand drive, I don't know if the engine layout is different for a LHD. The PCM module is located in the passenger (near) side wheel arch. You need to remove the wheel and arch liner to get at it (Mine has the protective cover over the connectors with a shear bolt which I don't have tools to remove). You don’t have to take the wheel/liner off but I found it gave me better access to the loom. The wiring loom from the PCM goes through the arch and at about 6 inches in to the engine bay (pretty much under the bottom radiator hose) part of the loom goes up to the top. This bit of the loom is cable tied to the inner wing. This contains the pink control wire which then goes across to the fan controller. My pink wire was broken/corroded at the point the loom separates in the bottom of the bay. There are two reasons for this. The first is that the cable firstly bends to the left and then is bent back on itself to go the wheel arch and taped up so that there is too tight a bend in the wire. The second reason is that this join is below the washer fluid bottle and water dribbles down into the join which over time corrodes the wire. What I learnt when fixing the problem: It is much easier to access from the bottom of the engine bay. I started trying to un-tape the loom from the top (After removing the air filter box). After removing the wheel arch liner, I discovered it was much easier to access from the bottom and removing the liner gives you more room to manoeuvre your arms. You will have to remove a fair amount of tape and some conduit from the loom to work out which wire it is but there are only a couple of pink wires in that part of the loom and I think only one that has a tight bend. I cut out the bent/corroded piece of wire and replaced it. I have read on some forums that any fault codes need to be reset before the fan will work again. I didn’t reset my code (P145C, Fan System Component A) and it worked anyway. The attached pictures show 1) A picture of the PWM signal on the pink wire viewed on an oscilloscope. This is with the fan full on. 2) a picture of the wiring loom from above after removing tape/conduit - This taken with the air intake box removed. 3) The small section of wire that I removed and the break/corrosion in the middle 4) A view of the PCM module inside the wheel arch with the liner removed 5) A picture of the wiring loom from below with the pink wire cut out Hopefully all of this info will be useful to someone……