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Aftermarket Fans, Standalone Ecu, and Factory Wiring

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wishihadatalon

20+ Year Contributor
2,615
72
Aug 18, 2002
Grand Rapids, Michigan
So I have a 95 TSI AWD with a Megasquirt ECU. Before I was using the A/C on switch to control just one fan which wasn't very good, but now I have added another fan and I blow the 20amp fuse when I try to turn on the fans (this makes sense to me). I have an output on the megasquirt that I can use to control the fans, but looking at the factory ecu pin out, I am not quite sure which wires control the relays. I've tried pin 20 before and had no luck getting the fans to turn on when the MS ecu output comes on. Any ideas on what wires I should use?

Additionally, do you know what voltage is supplied to the relays?

Thanks.
 
Can't help on the exact ecu pin... But I run a 30 amp fuse for my fan.

For the relay it should see +12v. What pin are you using on MS? Most likely it's switch to ground so you would need +12v to pins 30 and 86 of the relay. Pin 85 would connect to the MS pin. Pin 87 would be the +12v to the fans.


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I used that for wiring the fans. The problem is the ecu doesn't have a temp reference, so the fans don't work properly. Because of this, I am looking at controlling it with the m.s. Do you know if 20 or 21 is for the passenger side fan? Thanks
 
I don't know anything about Megasquirt ECU. Does it replace the factory ECU? What do you mean the ECU doesn't have a temp reference (no ECT temp sensor?) - you mean the Megasquirt one or factory one or??? How is it supposed to control the fans then? Factory ECU pins 20 & 21 aren't for one fan or the other - my link in post 3 explains how they're used - both pins control speeds of both fans.

If your ECU(s) have no way or controlling fans you may have to do:
1) Manual override: http://www.dsmtuners.com/threads/cooling-issue-plus-wiring-them-up.273645/#post-151319397 or

2) Use new relay for both fans activated by engine running: http://www.dsmtuners.com/threads/ho...come-on-when-car-is-on.281438/#post-151391082.
 
Megasquirt can be a full stand alone system or a piggy back. It can share sensors like that put out a voltage signal. It can't share sensors like temperature, throttle position, intake air temp.

That's why he is saying the stock ecu doesn't see any temperature. The temp sensor is hooked to the MS now.
 
I have both the factory ecu to keep the gauge cluster working and megasquirt for engone management. I have replace the factory coolant temp sensor with a GM one for the megasquirt, so the factory ecu doesn't get coolant temp input. Perhaps I will try a factory sensor for the time being and see if that works.
 
Okay, I made some progress on this tonight. With ECU wires 20 or 21 hooked up to my megasquirt output, I can get control of the main fan. Now I am looking for the signal wire for the a/c fan. From the ecu pinout on vfaq, I would assume it is either 22 or 45. Any insight on this before I start cutting more wires on my harness?

Thanks,

TJ
 
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