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Aux output puzzle


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Radiator fan connected to Aux output 7. Temperature on set to 92 degree C, hysteresis 4 degree, polarity low. Car powered Ign. swith pos 2, engine not running, fan is off. When changing polarity to high fan goes on but is set to low. When powering down the ECU the fan goes on... This would suggest the ECU is driving to ground when power is off, this isn't the way it should behave is it?

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This problem is usually caused by back feeding.  Fans relays are often driven by an ACC signal from the key so they can be run with the key in ACC position for the air conditioner.  The positive side of the relays coil will be ACC fed and the negative side goes back to the ECU.  The ECU has internal flywheeling diodes on to the power supply to prevent transient spikes and provide current averaging.  When the ECU powers down, any solenoid or relay wired to an ACC fed or hot fed supply must also be powered down.

Either wire another relay between the ECU and the factory fan relay (make sure to power the relays coil with the ECU's power supply) or wire the fan to a non flywheeled channel (Aux3 and Aux4 on an LEM G3, spare ignition and injection channels are also not flywheeled).

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  • 2 weeks later...

OK, changed the setup and all appears to be working now. Engine is up and running now. I did change to Aux 4 btw but it didn't make any difference before the change. Also I would like to thank you guys for the very informative tech mail I received about this "issue". Nice to know the people of Link care!

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