woodwright

I'm swapping engines in my 2000 Silverado. The new engine came out of a 2001 suburban. The only difference I have found is the sensor on the drivers side rear, right above the oil filter. On the one engine it's round and angles up into the water jacket and takes a 3 wire plug. On the other engine it's plugged off. I've been looking for a sensor diagram for 2 days and found nothing. What's it for? Thanks.