I think I have this figured out about the FANC override....

[blacksi76]

2000 Civic SI , H22 Turbo
S300 with built in OBD2B ECU Connector....with OBD2B factory civic harness

fanc-relay-wiring.gif

Spunkster, I saw this image you posted in another post here about the FANC over-ride, I checked my helmes manual, and my haynes manual, and pin A12 is A20 FANC (Green wire) on my OBD2B harness. That wire goes to the Engine Coolant Temperature Switch that connects to the Thermostat housing. There are two wires, the Green(A20) and a black(ground).... I am running a T1 Koyo half rad, SPAL Fan and shroud combo which came with the aftermarket Relay which I have wired up like this:

BLK/RED (oem rad fan connector) = 85
BLK (oem rad fan connector) = 86
user's 20A fused +12vdc = 30
user's wire to SPAL Red/+12vdc = 87
SPAL Black/GND = Chassic Ground

So using your Diagram, then I would not use the OEM fan connectors on 85 and 86 at all, just wire the A12(A20) Green Thermoswitch wire to 85, SPAL fan red wire to 87 with SPAL fan ground to chassis, and switch my 12v power source to 86 and tap 30 into 86....I was using a 12vdc right off the fusebox, is it neseccary to switch it to a 12v switched source? Thanks

[Spunkster]

It should always be a switched power source.

[blacksi76]

ok so if I switch the power source to a 12v switched, am I correct? I don't use the factory rad power connector wires because I am now using the ECU to control the fan and supplying a 12v switched power source?? Just wire it as you have show and I should be good to go...I don;t have to add an extra relay because I am already using an aftermarket relay...

[Spunkster]

No, the Fan should still be controlled via the original thermoswitch. The ECU control is a backup you can over ride this with. The fan should still operate normally without the ECU controlling the fan.

[blacksi76]

Ok, so I haven't been able to get the S300 to override the fan, yet the factory themoswitch does turn on the fan at the factory presets, so what am I suposed to do to override the fan so I can control it via the s300?

[Spunkster]

You will have to wire the ECUs fan control output into the relay that is controlling the fans.

[blacksi76]

on my car, there is only one wire (Green) on the harness for FANC that runs directly to the thermoswitch on the thermostat housing...

[blacksi76]

my harness is a civic OBD2B
I am here looking at the wiring diagrams:

I have the Engine Coolant Temp Switch A - 2 wires, one green which goes to a junction connector and one green goes directly to the ECU (FANC A12/A20) and from the junction connector, another Green goes directly to the under-hood fuse/relay box into the Radiator fan Relay.

I also have the black/red wire then that comes from the radiator fan relay, and goes directly to the Radiator fan motor which powers the OEM fan.

There is also the ECT sensor which has a Red/white wire that goes directly to the ECU and a green/black wire that goes to a Junction connector which seems to me to be just a negative ground for a bunch of sensors cause they all are green/black wires at the junction connector.

what do you think??

[blacksi76]

OR .....now that I am using an aftermarket relay to power my fan, I take the green FANC wire that is going to the factory underhood fusebox fan control relay, and re-route it to the new aftermarket relay? That would keep the wires that goes to the Thermostats switch intact and connected and the wires from the ECU A12/A20 ( OBD2B ) intact ata the ECU????

So I unbolt the Underhood fusebox and snip that green fan control wire and just run it to the new relay??

[Spunkster]

Try wiring it to the new relay.

[blacksi76]

the green wire going to the factory relay under the fusebox? wire that as A12/A20..

[blacksi76]

Using the Nitrous AUX 1 to control, the fan....this is what one guy did that worked....what do you think??

fandiagram.jpg

[Spunkster]

It may work, but you should also be able to wire the relay to the FANC output to have it also turn the fans on (besides the thermo switch).

[blacksi76]

if I take that FANC wire from the underneath the fusebox under the hood, and connect that to my aftermarket relay....will that effect the black/red wire that comes from the factory relay in the fusebox and is conected to my aftermarket relay now?

[Spunkster]

Just run a wire from the FANC output on the ECU to the relay that is controlling the fans.