Northern Banana Posted May 5, 2022 Share Posted May 5, 2022 Car Sigma 1.6 vtt 270r (race car)Could anyone enlighten me as to how the cooling fan is wired/powered in these cars.I'm having an issue with voltage drop at the ECU when the fan kick in 97 degrees.When cold and the fan not running I get 12v at the fan plug, when it reaches 97 and gets the signal from the ECU it reads 12.5-13.5v is that slight increase in voltage what switches on the fan? This doesn't seem right.Obviously being a race car it may have been modified but can't get my head around how its configured. Thanks Link to comment Share on other sites More sharing options...
Jonathan Kay Posted May 5, 2022 Share Posted May 5, 2022 If you'd like a wiring diagram please send me a Private Message with your email address.Jonathan Link to comment Share on other sites More sharing options...
Jonathan Kay Posted May 5, 2022 Share Posted May 5, 2022 "When cold and the fan not running I get 12v at the fan plug, when it reaches 97 and gets the signal from the ECU it reads 12.5-13.5v is that slight increase in voltage what switches on the fan?"Where are you putting the other probe?And what colours are the wires to the fan motor?Jonathan Link to comment Share on other sites More sharing options...
Northern Banana Posted May 5, 2022 Author Share Posted May 5, 2022 Positive to the fan is black/green. Link to comment Share on other sites More sharing options...
Jonathan Kay Posted May 6, 2022 Share Posted May 6, 2022 I don't understand what you're observing. Black/Green is the usual colour for the feed to the fan. Is there a Black earth in the same connector?I suggest disconnecting at that connector and measuring the voltage between the two terminals on the chassis side of the connector. Ignition OFF. Ignition ON but engine cold.Jonathan Link to comment Share on other sites More sharing options...
aerobod - near CYYC Posted May 6, 2022 Share Posted May 6, 2022 If it is a standard Sigma wiring loom, the ECU Pin 33 connects to the engine harness plug which then connects to the fuse/relay panel bottom relay. The relay then activates the Rad Fan. The signal wire from the ECU to relay is black/pink and the 12V supply wire from the relay to fan is black/green. It also looks like the Rad Fan Switch can also activate the Rad Fan relay independent of the ECU.The black wire on the Rad Fan should end in a crimp with half a dozen other wires that then end in a ring terminal on the chassis and the Rad Fan black wire should also connect to the black wire on the Rad Fan Switch.Black/green to ground should be 0V when the fan is off and black/pink wire is 0v from the ECU or switch, when the black/pink voltage goes to 12V, then black/green should go to battery voltage and the fan switches on. Link to comment Share on other sites More sharing options...
Northern Banana Posted May 9, 2022 Author Share Posted May 9, 2022 Sorry for the delay replying. Thank you for all your advice, its really helpful for someone with only a basic knowledge and 4hrs minimum drive from a knowledgeable caterham specialist.I'm hoping to get into the workshop later on today and will work through the above. <Many thanks Link to comment Share on other sites More sharing options...
Northern Banana Posted May 9, 2022 Author Share Posted May 9, 2022 This mornings findingsWith master switch off and ignition off - zero voltage to cooling fan (reading taken from T plug connector)When I turn on master switch (ignition still off) I get 11.16v at the fan T connectorIf I connect the fan up in this state it doesn't run so assuming fan needs minimum 12v to operate.If I unplug all relays (I have 4 under the dash) I still get 11.16v at the fan T connector. Same 11.16v with ignition on, engine not runningSame 11.16v with engine running13.2v when coolant reaches 97 degrees (when T connector plugged in fan runs, this is when voltage drops at ECU occur) I suspect we have to assume that the race cars wiring does vary for the road/standard car. As soon as you switch on the master switch (ignition off) the fuel pump primes. When the variable valve timing variant was introduced Caterham had bespoke looms produced to removed all the unnecessary ancillary stuff. When I look at the relay pic below it doesn't correlate to the wiring colours referred to in the wiring loom. Link to comment Share on other sites More sharing options...
Jonathan Kay Posted May 9, 2022 Share Posted May 9, 2022 "With master switch off and ignition off - zero voltage to cooling fan (reading taken from T plug connector)When I turn on master switch (ignition still off) I get 11.16v at the fan T connector"That's with the connector separated? And the voltage between the two terminals in the connector?Jonathan Link to comment Share on other sites More sharing options...
Jonathan Kay Posted May 9, 2022 Share Posted May 9, 2022 "When I look at the relay pic below it doesn't correlate to the wiring colours referred to in the wiring loom. "If you can post which relay is which we can try to identify the appropriate diagram.Jonathan Link to comment Share on other sites More sharing options...
Northern Banana Posted May 9, 2022 Author Share Posted May 9, 2022 "That's with the connector separated? And the voltage between the two terminals in the connector?"Yes, also double checked with earth to chassis. Link to comment Share on other sites More sharing options...
Jonathan Kay Posted May 9, 2022 Share Posted May 9, 2022 Thanks.I don't think that the difference between 11.6 V and 13.2 V is turning the fan motor on.I wonder if that 11.6 V is coming from another circuit that won't supply much current."Same 11.16v with ignition on, engine not running""Same 11.16v with engine running"What's the voltage at the battery when you observe those at the connector?Jonathan Link to comment Share on other sites More sharing options...
Northern Banana Posted May 9, 2022 Author Share Posted May 9, 2022 12.5v at the battery."I don't think that the difference between 11.6 V and 13.2 V is turning the fan motor on.I wonder if that 11.6 V is coming from another circuit that won't supply much current."I would agree. One line of thought is that if there is a parasitic power supply, when the switch properly opens at 97 degrees and delivers a full 12v+ it is causing the issues with current heading back up the source of the parasitic supply. However if I let the temps rise beyond 97 degrees with the fan T connector disconnected I don't see the voltage drop at the ECU. Link to comment Share on other sites More sharing options...
Jonathan Kay Posted May 9, 2022 Share Posted May 9, 2022 It might be possible to test that idea by measuring the voltage between the terminals (and across the fan motor) with the connector (and the fan motor) connected...Jonathan Link to comment Share on other sites More sharing options...
Northern Banana Posted May 9, 2022 Author Share Posted May 9, 2022 JK,Have you come across this wiring diagram before?https://andrewrevill.co.uk/Downloads/Wiring%20Diagram%20-%20Main%20Vehicle%20Loom%20-%20Corrected.png Link to comment Share on other sites More sharing options...
Jonathan Kay Posted May 9, 2022 Share Posted May 9, 2022 Yes. That's Andrew's corrected version of the factory wiring diagram for a main vehicle loom... probably a late K.Jonathan Link to comment Share on other sites More sharing options...
Northern Banana Posted May 9, 2022 Author Share Posted May 9, 2022 OK I'm going to pop up a new post to see if anyone has a wiring diagram for the vtti race cars. Link to comment Share on other sites More sharing options...
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