gwgw Posted July 9, 2016 Share Posted July 9, 2016 Hi everyone, i hope you can help: I've also posted this on the Fiat forum, so here goes: One cooling fan is constantly on as soon as the ignition key it turned, the other is off. So far I have replaced the radiator temp.,sensor blue in colour. Also the air temperature sensor in the radiator cowling, black with green coil. I have also replaced the two relay units. which has not rectified the fault... if anyone has the wiring diagram it would be most welcome. I can only assume that there is a cable broken, and there is some kind of failsafe system activated. Its a fiat ducatto based motorhome 1999 2.8 turbo diesel... Any advise would be gratefully received. I notice another post had a similar problem but no update was posted on how it was rectified. Many thanks a frustrated fiat ducatto owner. :-D :-D :-D Link to comment Share on other sites More sharing options...
Alanb Posted July 9, 2016 Share Posted July 9, 2016 Welcome to the Forum, As you have already deduced the fans are controlled by relays T06 and T07, mounted in the engine bay panel CVM. I have some further info, but I cannot vouch for its accuracy. Use the following as a guide only. The appropriate circuit description reads as follows. "On the basis of data supplied by the engine coolant temperature K036, engine management unit M001, excites (energises) the relay(s) coil(s) via a negative signal and thus supplies the fans with power." I suspect that, that is not much help. The sensor K036 is shown as being behind the LH headlamp assembly. However on peering into my 2006 2.8 JTD, I have not managed to locate it! I case they are of any help these are the wiring details given on the documentation that I have. From sensor pin 1 to ECU pin B85 Light Red (Italian HR), from sensor pin 2 to ECU pin B84 Violet/Black (ZN). Does this match the colours to the sensor that you have changed? Control outputs from the ECU pin A19 to CVM A20 (T06 control) is Yellow (G, giallo), and from ECU pin A20 to CVM A28 is Grey/Black (HN), for relay T07. There may be errors my translation of the Italian abbreviations, so I have included the original codes in brackets. If you discount an ECU fault, consider the possibility of an earth fault due to chafed wiring. Is they ECU giving any alarms? I do not think that I can help furthe,r but please do post the final outcome. Link to comment Share on other sites More sharing options...
Alanb Posted July 9, 2016 Share Posted July 9, 2016 Welcome to the Forum, As you have already deduced the fans are controlled by relays T06 and T07, mounted in the engine bay panel CVM. I have some further info, but I cannot vouch for its accuracy. Use the following as a guide only. The appropriate circuit description reads as follows. "On the basis of data supplied by the engine coolant temperature K036, engine management unit M001, excites (energises) the relay(s) coil(s) via a negative signal and thus supplies the fans with power." I suspect that, that is not much help. The sensor K036 is shown as being behind the LH headlamp assembly. However on peering into my 2006 2.8 JTD, I have not managed to locate it! I case they are of any help these are the wiring details given on the documentation that I have. From sensor pin 1 to ECU pin B85 Light Red (Italian HR), from sensor pin 2 to ECU pin B84 Violet/Black (ZN). Does this match the colours to the sensor that you have changed? Control outputs from the ECU pin A19 to CVM A20 (T06 control) is Yellow (G, giallo), and from ECU pin A20 to CVM A28 is Grey/Black (HN), for relay T07. There may be errors my translation of the Italian abbreviations, so I have included the original codes in brackets. If you discount an ECU fault, consider the possibility of an earth fault due to chafed wiring. Is they ECU giving any alarms? I do not think that I can help further, but please do post the final outcome. Link to comment Share on other sites More sharing options...
thebishbus Posted July 10, 2016 Share Posted July 10, 2016 I think this is correct for your engine. The fan temperatur switch is fitted to the rear of the lower radiator part. ( botton nearside corner ). The coolant temperature switches are fitted into the thermostat housing. ( attached to the end of the head ) Brian B, Link to comment Share on other sites More sharing options...
gwgw Posted July 10, 2016 Author Share Posted July 10, 2016 Thanks Alan, however mine does not have an ECU as it is 1999. I'm investigating the wiring and will post my findings later on. cheers Link to comment Share on other sites More sharing options...
gwgw Posted July 10, 2016 Author Share Posted July 10, 2016 Thanks Brian, on mine there are only two wires at the thermostat housing and i believe these are for the temperature gauge. cheers Link to comment Share on other sites More sharing options...
thebishbus Posted July 10, 2016 Share Posted July 10, 2016 The sensor / switch for switching the fans on and off is the one mentioned at the bottom of the radiator ( near side ) in accordance with the coolant temperature. Brian B. Link to comment Share on other sites More sharing options...
BrianBW Posted July 10, 2016 Share Posted July 10, 2016 See my web site for hints/solution: www.ourwanderer.uk Brian Link to comment Share on other sites More sharing options...
thebishbus Posted July 10, 2016 Share Posted July 10, 2016 Having read the OP again I see that one fan is running all of the time . I belive the cooling is in two stages. Stage 1, one fan running and stage 2, both fans running depending on temerature. Both are switched by the switch in the bottom of the radiator. If is not the switch I would suspect a short circuit in the wiring. Brian B. Link to comment Share on other sites More sharing options...
Alanb Posted July 10, 2016 Share Posted July 10, 2016 Hi, This is beginning to sound like the twin thermostat that I had to change on my 1990 2.5 Turbo Talbot Express many years ago. I was suffering from frequent short blips on the cooling fan. Took some diagnosing as the fan did not really start, it just blipped the vehicle 12V system. This may have been an early step on the track to continuous operation. As suggested above, it was situated towards the bottom rear of the radiator, but I cannot remember which side. As I am an inveterate and ancient hoarder, I still have the offending twin thermostat. It has a stepped 22mm max dia black plastic body, nominal 29mm hexagonal brass end with 22mm threaded end into radiator It is a 3 wire device red to single male 4mm connector, black and white wires to a twin male/female white connector with the black wire to the female connector. I therefore presume that the black wire was the common earth connection to the twin thermostat contacts. This unit is of course older than your vehicle, so the design could have changed. Link to comment Share on other sites More sharing options...
gwgw Posted July 17, 2016 Author Share Posted July 17, 2016 Hi again, i removed the blue sensor switch. I then shorted out two of the three wires, this kicked in the nearside fan. The strange thing is this happened whilst all three relays were removed from the rad cowling. Surely the sensor switch operates the relay as the wires are small in size. I checked voltage at the sensor and the one of the three wires is live as soon as the ignition is switched on. Any suggestions are most welcome Thanks Link to comment Share on other sites More sharing options...
Alanb Posted July 18, 2016 Share Posted July 18, 2016 Hi gwgw, I would expect, as do you, that the fans would be controlled via relays. A fan running with a relay removed begs the question, have you identified the correct relays? Standard practice appears to involve controlling the relays by the negative lead. With this configuration, looking into the wiring harness towards the relays, from the thermostat, with the ignition ON, I would expect to see two wires reading about 12V positive, from the relay coil terminals 85, and one earth connection. Have you checked the thermostat? There should be no connection through it at ambient temperature. ______________________________________________________________________________ I have located some old notes in a notebook kept for my 1990 Talbot Express. Given here in case they of use. Fan 1 (LH) cut in 88 deg, off at 83 deg, harness wire colour to relay Bk/Vl, relay socket coloured white. Fan 2 (RH) cut in 92 deg, off at 87 deg, harness wire colour to relay Pk/Bk, relay socket coloured red. The above refers to the relay coil connections from the thermostat. The relays were of the "standard" automotive type, and THINK that they were located in the dashboard, behind the instrument panel. Link to comment Share on other sites More sharing options...
gwgw Posted July 19, 2016 Author Share Posted July 19, 2016 Hi again and thanks for reply, strange thing about the relays are with the fan running if i remove the appropriate relay the fan goes off. But as mentioned before if i remove the relays and short out two of the three wires on the blue sensor switch the fan will power up. I'll check out the voltages at the relays when i get a chance. Cheers Link to comment Share on other sites More sharing options...
gwgw Posted August 13, 2016 Author Share Posted August 13, 2016 Finally sorted it. I basically followed the wires from the switching side of the fan relay, these went down towards the floor then across by the starter motor and then up towards the battery. From there they headed toward the rhs headlight, it was here i found the cable [very small in diameter] had broken. Soldered it up and all works perfect. Thanks to those who replied. :-D :-D Link to comment Share on other sites More sharing options...
Alanb Posted August 13, 2016 Share Posted August 13, 2016 Congratulations on your success. Still cannot understand how fans operated with relays removed. That i s where a circuit diagram would be useful. Your taking time to post the solution is appreciated. Link to comment Share on other sites More sharing options...
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