Trailblazer 2002, trans vent hose discharges some oil

If the fluid is a dark reddy/browny colour it's transmission oil. If the transmission cooling connectors into the radiator can't be replaced, you will need to replace the entire radiator. Check hoses and lines, clamps etc as it might only be a minor leak or fault.

Disconnect the hose (s) from the oil cooler line ( some oil might drip from the hose ) change the fitting, reconnect the hose, start the car and check the fitting and hose connection ( clamp ) for leaks ( tight as necessary ) move the transmission shifter thru all the gears and check the transmission oil level.

Transfer case switch may be bad allowing trans fluid in vac. Lines and can reach as far as heater switch common problem fix these all the time 17 bucks for tranfer case switch and 20 foot of vacume hose and replace all the vac. Hose because this issue causes pcv to not work correctly so the moisture from crank case ends up going out the distributor vents causing cap and rotor corrosion there is service bulletin to remove distributor vent screens i would fix that since you will be working next to it any way

Where in relation to the car's underside is this fluid coming from?

Side: Check washer bottle reservoir, any fluid filled engine mounts, and power steering hoses and reservoir.

Middle: Check engine sump, front and rear crankshaft seals, and gearbox seals.

Also if you drive with the airconditioning on, then the airconditioning drain vent for condensation is usually just slightly off centre, behind the engine. This is normal though, and doesn't constitute a fault.

If you can jack your vehicle up and inspect it, this would be the best thing.

Good luck.

You cannot repair the leak until you determine where it is leaking. More than likely it is leaking from the oil filter, oil pressure sending unit, or valve cover gasket. Check around the oil filter for a leaks and if you see oil on the filter then replace it. Check the oil pressure sending unit and if it is leaking replace it. Wipe all the oil off the bottom of the engine and any other place you see oil. Now place newspapers on the floor under the car and then start the engine and let it run for about 10 minutes and then shut down. Wait overnight and you can see where the leak is coming from.

Vacuum hose for air vents is not connected. These black hoses should be accessable by feeling under the dashboard. The hose just slides onto the air vent intake. Hope this helped.

sounds like a vac line leak or actuater problem

Unless this happens in the rain as well, I would not worry about it. Likely in the car wash, far more water is coming in than the normal drain system can handle, therefore causing it to overflow. If you do have a drain obstruction, find the drain hose (small right angle hose on firewall passenger side) and roll it in your fingers to clear it.

im not that familiar with hummers but it sounds like youve found the end of the transmission vent hose or possibly the front differential vent hose and they will have seepage of oil sometimes. however if its a constant oil drippage, then there could be a buildup of pressure inside tranny or rearend. if u follow the hose down to its beginning youll know if its the trans. or differential(rearend). it might be normal to see this fluid,or it could be too much fluid inside trany/rear.

theres alot of 2002 chevys of different kinds but they all can get a vacume leak the 3.1 and 3.4 even the 4.3 and the 5.7 blow intake gaskets. un plug the pcv valve and the vent hose from the valve cover to the air cleaner hose. plug the holes good with tape and rags till sealed if it runs smooth ar idle then the intake is leaking. Coming into cold weather I did then as fast as I could as there was always another one in the parking lot. Leak coolant too. about half and half, some both. a few were driven too far they were blown. Plug wires and injectores dropping out will do it too. but check engine light on with codes P0300 or any code P0301-308. Vacume leak can set all kinds of stuff from map senser, cam senser Egr back pressure, ramdom cylinder miss to certain cylinder miss. and the leak will be the problem not the sensers or wires