I've got a sensor/connector which was sitting just forward of the ECU on my 2007 3.2L XC90 which wasn't connected to anything? I think it might be an optical crash, or ambient temp sensor (randomly different, I know)? It's got P/N: 9456721 on it, which is listed as a Cover in the ECU Harness, but does not identify the actual sensor (item 18 in attached link https://parts.volvocarsofphoenix.com...2/9456721.html). Please help, I've currently got it sitting near the intake grill to get ambient air temp (if that's what it's for...).

My wife lost all of her coolant in a heatwave here, and I've got a check engine light. I've tracked down several problems as a result. I've proven the electrical radiator fan has a burnt out contact on it, and also found a torn PCV valve (and consequently just replaced both), so I'm not sure which one would have been causing this engine light, or if it's this sensor (or maybe it's all of them?). I normally like to only change one thing at once to verify a problem's fixed, but I found all of this stuff broken, so needed to change it all.

I haven't started the engine yet, as I really want to know what this sensor is.

Thanks for any help you can provide. P/N: 9456721. Note, it's both halves of the connector in one assembly.
Note the frame clip on the bottom of connector

 

That isn't a sensor. That is an unused electrical connector with a dummy plug in it to keep junk out of it.