Jsdirt

Sounds to me like the pump has failed, but it could be an air pocket from improper servicing. What I do in those cases to verify that, is use my hands to feel the cylinder head and hose temperatures as it idles from a cold start. The T-stat isn't going to be open, so you can eliminate the 2 big hoses and radiator from that test. Coolant should be circulating through the heater core and a few bypass hoses. If the heads start getting uncomfortable to hold a finger on, yet all the bypass and heater hoses are cold, you've got zero circulation due to either a failed pump, or a giant air pocket. Most newer vehicles like this require coolant to be charged back into the system under vacuum, otherwise the system will not be full, and this problem can happen.

When it won't start, you'll need to find what you're missing and go from there. Spark, fuel, or both. Once you find out what is missing, you can troubleshoot from there. More than likely there's either a failing cube relay in the underhood fuse box, a corroded fuse or one that has bad pin contact / continuity, a failing module, or damaged wiring.

Easiest thing to do is just grab it from where it currently plugs into the horn now. Use that power to control the relay, and run separate, dedicated power wires to the horn.

FYI Duelin, I got a 404 on that link. Ahh, I see what happened - the link got posted twice right next to each, so it's trying to go to the double address. http://www.k0bg.com/wiring.html What an excellent article!! Thanks, Duelin!

If it were mine, I'd run the current through the sensor, just so the ECU knows how much is being used so that it can charge the battery accordingly. From my experience it seems they put fuel mileage as a priority over battery life. I'd personally prefer that reversed, but this is the world we live in. That's my reasoning for going through the sensor - the battery is going to need all the help it can get to make it just 6 years (When they used to last 8-10 on average without electronics).

I've seen strange things like a missing ignition ground cause battery drain before. I'd concentrate on the short circuit in the circuit that fuse is protecting, and go from there.

Don't have any idea what you're working on here, but this is a classic symptom of a bad o2 sensor. When you first fire it up, it's running in open loop. When in open loop, NONE of the sensors are being used to calculate fueling requirements - it's all pre-programmed in the engine computer. Once things are warm enough, it switches to closed loop, which then uses ALL sensors to calculate fueling. Should be throwing rich codes, and possibly o2 codes. Posting whatever codes it has would be super helpful, along with year, make, model. Pretty simple to troubleshoot watching live data on a scan tool. If the upstream sensor isn't switching from rich to lean at a rapid pace, and is just hanging at a high voltage (.7v-.9v), you've got bad sensor wiring or a bad sensor. Unplugged the scan tool should show .450v - if it shows this, wiring integrity is good. Another possibility is a stuck open EVAP purge valve with a flooded charcoal canister (If filled to the brim, and you forced a few more "clicks" at the pump in there). Scan data and codes will tell the tale. Just FYI, if this is a GM truck, 50 lbs. is on the low side. Should be 55 - 60 psi. This could just be a gauge variance, though. I would concentrate on the problem at hand first.

Could just be out of refrigerant due to a condenser leak. Look for oily areas on the condenser, usually on the sides or bottom - that's a leaker. Extremely common problem in this model year range. Fuse is probably in the under hood fuse box. Could be a relay in there as well. If you jump the correct pins (Be advised if you jump the WRONG pins you COULD smoke the computer) on the relay and the clutch engages, then everything circuit-wise is good - wiring, pressure switch, clutch coil. You will then need to figure out why it is not receiving the command for clutch engagement. Anything from low refrigerant to a faulty pressure sensor will do this. If the pressure sensor is saying there's 0 PSI ... or 600 PSI, the clutch will not engage.

You can add fluid underneath at the transmission, but for the amount in the radiator cooler, I wouldn't worry about it unless the transmission is now performing differently than before.

Ahh, gotcha. Didn't realize they have power opening now! Knowing GM they probably made the entire latch assembly completely different from the older models. Never know, though - I'd go to a parts site and compare part numbers, and see if you can find an actual picture of the assembly for comparison in case the part numbers don't match, but it ends up the same fitment. Absolutely NOTHING is easy anymore ... Best course of action would be to ask a junkyard, since they have access to fitment information. Although they may not be updated with '22 models yet.

If it were mine I'd just leave it unplugged. Quick, cheap, and easy. Fold up the excess wiring and zip tie it in a bundle, or just chop it off.

Your pressures look good there. You could have a dead segment in the armature, or bearings that are beginning to fail causing intermittent low pressure. You'll want to check out ALL wiring to the pump first before replacing anything. Either way, at the miles you're at, especially if that pump is OE original, I'd scrap it for a new one. Regulator is part of the pump assembly. I don't know where you're looking, but none of the pumps listed here mention a separate regulator: https://www.rockauto.com/en/catalog/chevrolet,2004,express+1500,5.3l+v8,1423954,fuel+&+air,fuel+pump+&+housing+assembly,10147 Always good practice to replace the ENTIRE assembly, not just the pump, since your fuel gauge relies on good contacts inside this unit as well. Be glad you've got a 800 series truck instead of the newer 900 series and up. Those have no return line, and rely on a fuel pump module, conveniently located above the spare tire where all the road salt gets tossed from all 4 wheels. So when your spare winch rusts out and you have to cut the hanger & cable off, then spend $200+ on a new module, you'll find it DOESN'T WORK without J-box programming (GM gets more money selling you the programming info), costing you even more money and downtime! Better hang on to that '04!

Sounds like it's still cable actuated since you worked it with the battery disconnected. Could be a failing brake switch, or the vehicle thinking it's one or more gears off from where it actually is. Could be an issue under the trans pan. I'm not familiar with the newer transmissions, but I'd bet on a problem there from what I've been hearing.

Sadly, this is the norm for GM V8's these days, but it's hit or miss. Grab 50 identical trucks and: 1.) All 50 may knock 2.) None of the 50 may knock 3.) Any combination thereof may knock The automotive industry today is a complete and total crapshoot (Shitshow, if I'm honest). Not knowing your mechanical aptitude, the knock could very well be lower-end rod knock, or, could be lifter knock. As you may or may not know, these engines are extremely failure prone, AND hit-or-miss, with lifter longevity. Most fail between 50k on the low end, to 180k on the high end. The majority seem to average a failure around 120k. Of course this depends heavily on maintenance, and oils used. The lifters are classic low-bidder junk GM tossed in an otherwise fantastic platform - par for the 21st century course, unfortunately for us consumers. They spin in their bores and self-destruct, or lock in either the open or closed position as it relates to AFM (Active Fuel Management - AKA, "4-cylinder mode"). Misfires accompanied by noise and high wear metal levels in the oil are the first clues. Also, the oil pump pickup tube o-ring is another high failure item (among a few other things).

The leak at the upper hose could be as simple as tightening a worm clamp, replacing a spring clamp ... or the hose has reached the end of its life, and/or the nipple where it lives needs a good cleaning. There are a couple failure-prone pot metal with plastic insert heater hose connections on the intake manifold - that could be running down the side of the block, along with these crappy plastic heater core connections at the firewall. The hoses themselves could be done for, too. Also could be weeping out of a leaky head gasket.