Are ECM outputs floating or tied high when they're not active?

[davepl]

For things like the fan relay triggers - do they float or are they +12V when not active?

I don't have a single modern ECM running at the moment, everything in boxes, or I'd just go measure one!

If anyone knows, please let me know.

[matty b]

Inputs or outputs? Outputs are open from the transistor out unless they are turned on and then depending on the output, could be pull to ground or apply voltage. Inputs are a totally different thing and will never be floating (at least not on a professionally build unit). Depending on whether the input senses ground or voltage, it will have a pullup or pulldown resistor tied to it. IF they float, stray voltage can cause a false triggering of that pin.

[davepl]

Thanks - it was the output I was wondering about (fan specifically) and from your description they just let them float, rather than tying them high when off for example.

[DSteck]

A digital output thats either high or low will float by nature if I'm not mistaken.

I've seen analog inputs float. Digital inputs never float.

[davepl]

Input needs to be pulled one direction or the other as a reference, don't they? I'm a software guy so be gentle.

Outputs either have the ground path needed to complete the relay's magnet circuit or they don't, so it doesn't really matter. But an input you'd want at the known end of some range, I'd think.

My question is answered above, though.

[Montecarlodrag]

They float. I have checked several times when troubleshooting and they have no voltage when not activated, just a little floating voltage (pretty low, + or -)

[matty b]

Electrically an output doesn't "float" as that assumes that there is potential on the circuit. I suppose you could say that is "floating" when a component is wired to it, but the component itself is what is floating not the output. With nothing wired to it, you will not see any positive or negative potential on it. Inputs are another story altogether and regardless if its a digital (on/off) or analog (resistance to ground) there is a pullup or pull down on it. If its a pullup, there will be a resistor of a higher value than that of the sensor that is connected to Vref and the other side to the input pin which is wired in parallel with the sensor. When the sensor is unpluugged, path of least resistance is through the pullup and why youll see 5v on the circuit when its open. Pulldowns are the same but tied to ground instead of voltage.

Also to clarify, think of an output as a simple light switch. When the switch is off, there is nothing "floating" per se. If the switch is on, if nothing is plugged into it, its the same as if the switch was never turned on in the first place. When we speak of floating in electronics, its voltage trying to find ground and will take the path of least resistance, even if its high resistance. In the case of a simple resistive load output, no ground or voltage path will be available for that voltage so it cannot float even though I guess it is in a literal sense.