What did you do to your NNBS GMT900 Tahoe/Yukon Today?

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Sparksalot

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Are you still getting the normal condensation dripping out of the evaporator and hitting the ground below the vehicle? If so your drain line is OK. If not, it’s plugged.

I have on occasion experienced the same phenomenon you described in multiple vehicles when the temperature and humidity were just right. The evaporator chills the air below the dew point and blows out a stream of fog. And under similar high humidity conditions moisture can condense on the exterior surfaces of cold HVAC parts like ductwork and the evaporator housing, and drip down.

The most effective way to combat the latter scenario is running the HVAC on recirculate so more humidity is not drawn in, and crank the fan speed up to reduce the temperature delta between the components and the air passing through. Once the interior humidity is dried down by the HVAC, the surface condensation should stop.
I’ve assumed It was leaving the normal puddle. I know ass you me.

I’ll have to specifically look the next time I’m out to verify.
 
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So a few observations concerning the oil pressure switch replacement I did.

I purchased the Lisle socket for this and I already had a shorter one that I've used on my mustang. I figured the GM switch would be too tall to use the shorter socket. It actually just fits and reaches to the hex.

When I went to remove the sensor I couldn't get the longer Lisle socket onto the hex of the sensor. It was like either that plastic shield or something was in the way and wouldn't give me the correct orientation to get it over the hex. I tried the old shorter socket I had and it went on with no problem. attached are a couple pics of that socket.

Also, the new sensor ended up in the same orientation as the one I took off when tightened. This may be why there is this opening in that plastic shield in front of the sensor, just in case it's oriented facing forward.

I spent most of my time trying to access and remove that connector just by feel and using different tools like picks, mini screwdrivers, etc. If I knew or had seen the opening beforehand it would've made this job so much easier and take half the time. Once that connector was unplugged it took maybe 5-10 minutes to get the old sensor out, remove the screen, and replace the new parts and plug it back in.

I also disconnected the PCV line from the back of the valve cover along with the evap line to get them out of the way. Also took the large vacuum line off the brake booster that runs past that area and moved it up over that plastic shield on the back of the engine, so the only line I had to work around back there was the braided fuel line.

20210629_172651.jpg
20210629_172631.jpg
 
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Also while in there doing the work some of the wire loom covering the wires going to the coils, especially the rear coil, were brittle and crumbled to pieces. Guess next project is to replace some of that split loom
 

Tonyrodz

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So a few observations concerning the oil pressure switch replacement I did.

I purchased the Lisle socket for this and I already had a shorter one that I've used on my mustang. I figured the GM switch would be too tall to use the shorter socket. It actually just fits and reaches to the hex.

When I went to remove the sensor I couldn't get the longer Lisle socket onto the hex of the sensor. It was like either that plastic shield or something was in the way and wouldn't give me the correct orientation to get it over the hex. I tried the old shorter socket I had and it went on with no problem. attached are a couple pics of that socket.

Also, the new sensor ended up in the same orientation as the one I took off when tightened. This may be why there is this opening in that plastic shield in front of the sensor, just in case it's oriented facing forward.

I spent most of my time trying to access and remove that connector just by feel and using different tools like picks, mini screwdrivers, etc. If I knew or had seen the opening beforehand it would've made this job so much easier and take half the time. Once that connector was unplugged it took maybe 5-10 minutes to get the old sensor out, remove the screen, and replace the new parts and plug it back in.

I also disconnected the PCV line from the back of the valve cover along with the evap line to get them out of the way. Also took the large vacuum line off the brake booster that runs past that area and moved it up over that plastic shield on the back of the engine, so the only line I had to work around back there was the braided fuel line.

View attachment 343502
View attachment 343503
Was the screen underneath clogged, or any debris in it?
 
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Nice. So a clogged filter wasn't part of your issue.
Nope, bad sensor.

Engine ran fine, just yellow engine light on and pressure gauge on zero. Checked DTC, got P0523 (engine oil pressure switch voltage too high). Cleared it, restarted and gauge slowly swept all the way to the other side and light came back on.

When this first came on, we were out shopping and just got back in vehicle to go home. I checked the oil level and it was fine, and there were no unusual noises from the engine. I figured it was just a bad sensor. The oil light never came on and never gave the "low oil pressure stop engine" message on the DIC. Drove it home 35 miles with the dead gauge and engine light on.
 

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