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Sigma Radiator fan wiring - Is this normal?


Northern Banana

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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

 

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"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

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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

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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.

IMG_2181.thumb.jpg.29ebe90dfce991827b313c6b0a52c4a9.jpg

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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

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This mornings findings

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

If 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 running

Same 11.16v with engine running

13.2v 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. 

IMG_2447.jpeg.9bf3cee32e7912f2992c96ff5ec3c467.jpeg

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"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

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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

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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.

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