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I rarely drive my 135000 mile 2004 Chevy 2500 since I retired, usually just to tow my home-built squareback trailer (2250 lbs) on camping trips. Before retirement, it was a hauler for my drag race car (for 5 years), towed my camper (for 9 years, now), and also my daily-driver (for 5 years, then part-time after I bought an HHR panel as my daily). The bed is full of camping gear and emergency-use supplies (about 800-1000 lbs), year-round, so it sits while other cars and trucks get more usage. After sitting for three months this time, I changed the oil, topped up some other fluids, and took a 500 mile trip with my trailer attached. Sometimes, if I started off too hard from a stoplight, the 4l80e felt like it was slipping, but not so much if I feathered it at the start. At first I wondered if it might've been a U-joint getting loose, but a quick test underneath proved it to be OK. Furthermore, when I pulled off into soft mud, it really slipped before it grabbed (two-wheel-drive). Though my 6.0L engine/4.10 rear combo has no trouble pulling the 2250 lb trailer, I started using tow/haul mode on the second half of the trip, whenever I was either braking in traffic in urban areas, or when taking off from a dead stop. No slippage when tow/haul is engaged. I had the solenoids upgraded about 50000 miles ago, when stop & go daily driving in rush hour traffic was causing erratic behavior, and I used Lucas Transmission Fix about 25000 miles back, when I felt a slight slamming into second gear (upon part throttle). In each case, the problems went away. I didn't check my transmission fluid before the trip, I confess, but I did check the tranny pan, rear seals, differential for signs of leaks, and found none. On the trip home, I stopped just around the corner and bought a new grease gun & cartridges (for the driveline, which may need some, though I did the front end 10k miles back), and a 24 oz bottle of Lucas Transmission Fix (if the fluid level is low, I'll just top up...if the level is OK, then I'll drain/siphon 24 oz and replace with Lucas). It worked before, so why not try it again?

New guy here with engine problems. All parts are stock. No modifications have been done to engine and engine management to our knowledge. With that said, here is what is going on. Truck is a 1996 GMC Sierra. Crew cab, long bed, C3500, non dually. Has 7.4 454 Vortec and 4l80e transmission. Driveline has 147,000 miles and engine has good compression. All cylinders read 120 to 140 PSI. What's going on is the engine refuses to run properly. First up is the MAF sensor. Had the engine light on the dash so I used our OBD2 scan reader on it. Got P0102 which is Mass Air Flow sensor low output. Replaced the sensor with a Bosch unit and cleared the code. Next engine start that same code came back. I checked all the wires and plugs that section of the harness goes through. It has a good run to the computer. No frays or breaks. I even reset all plugs thinking there might have been some resistance in the connectors. No dice. Code comes back every time I clear it. Any ideas? Next up is the really serious problem that prevents the engine from running properly when cold. Low fuel pressure. According to our gauge it only has 20 PSI max and leaks down as soon as the pump turns off. On the fuel system we have a new pump in tank, fresh filter, and new regulator. That was a pain to install as the top of the intake manifold had to come off. Still have the low pressure and leak down. We thought the injectors were leaky but the thing is lean at idle as we sprayed starting fluid in the intake tube and the idle evened out. When cold it doesn't want to idle at all but will even out at 650 to 750 RPM when warm. Any idea what is going on? We have no idea what type of pump is in the tank as the people who own the truck put it in before we were tasked with fixing it. Still have the stock one. We plan to pressure test it and if it can go up to at least 80 PSI we will just put it back in and see what happens. So, any ideas on what is going on? I can record videos if any of you want to see the engine and hear it running. If anyone can figure this out I would greatly appreciate it as this goes beyond my knowledge of fuel injection problems.

I was wondering if anyone has had this problem with there 4L80e transmissions. On my truck the transmission overheats when driving with no load on rather mild days (75 degrees F). My truck is a 2006 2500hd 6.0l 4x4 and I have an extra trans cooler in addition to the factory auxiliary cooler. Initially I was thinking that my coolers were plugged because the line coming from the transmission was hot and the line returning from the coolers was the same as ambient temp. Thinking that the coolers were plugged I tried flushing them, forward and reverse, I even removed them, and I still get that condition of one cooling line being hot and the other being cold. I started to think that maybe the cooling lines have a blockage so i flushed them as well (both forward and reverse) but still the same problem ( i also verified that the radiator did not have a blockage since the heat in the line is past the radiator). Since this did not work I took the truck in to have the transmission flushed just in case there was something going on the the transmission. The shop checkout the pan, filter and fluid and said it looked good (no metal shavings, minimal debris, not burnt). This shop used the HotFlush system to flush the system. Even after the flush the same problem. The system is acting like the transmission is not letting the oil back into the transmission from the oil cooler return line. Does anyone here know what could be causing this? Outside of this issue the transmission is stock and is running fine. please help thanks

So I’ve searched all over and can’t seem to get a straight answer to what I’m experiencing. So I have a Black Bear Tuned 03 GMC Sierra 1500HD with the 4L80E 4 Speed Automatic transmission with the ability to Manually shift 1-2-3. My understanding is that when I Manually shift it down into 1st gear it’s suppose to lock it into 1st gear so it revs up way higher and engine brakes to slow down but does not shift until I manually shift up to 2 or 3 or put it back in Drive. Well when I lock it into 1st gear, the revs are much higher but it still automatically shifts to 2nd gear once I get close to 25-30mph even though I have 1st gear selected. Is Manual shift lock not working for me? Has anyone else experienced this? I just don’t get the point of manual shifting if it’s still gonna shift up automatically anyway Thanks for any input!

Please Help. We're working on a 2001 Chevy Silverado 2500HD.It was stuck in limp mode. We first got the P0783-85 codes, so we replaced both shift solenoids, as well as the wiring harness. Still shot the same codes and was stuck in limp mode. So we replaced the transmission. Still didn't work. Now it's pulling up P1860 and both shift solenoid again. Also I realized it was shooting these codes before I even put it in gear. And that's what makes me think it's the ignition switch. Any help at all will be greatly appreciated and save my sanity.

Hello! To whomever may have any advice. I recently bought a 2005 gmc single cab with a 6.0 4l80e that wouldn’t start unless you put a little fuel down the intake and jump the starter(which I didn’t do bc I’d rather fix the problem logically). Anyways so a problem that I found is that he had actually broken the ignition interlock cable on the steering column and you were actually able to turn the key by hand but turning it to the start position wouldn’t do anything other than a like if you would say meh out loud that’s literally what the engine or I believe the electrical would sound like when you turned the key into that position. So I replaced the wire from a donor steering column which was a PAIN!!! anyways I have the original column in with the new wire but it’s still not trying to start at all. I also noticed that the throttle body doesn’t open when you press the Gas and you can’t push it open. It also makes a small humming noise like it wants to try to open and slightly vibrates. Also so I jumped the 87 pin on the starter relay to the positive and the engine turns over but won’t fire and start. I’m assuming that it’s a fuel problem(yes I put fuel in the tank today 7gals). So my next theory is going to maybe test the starter? I’m not really educated on this stuff but I do have the tools for the most part. Any advice would be appreciated. ALSO it has a newer ignition Solenoid and it has the lock and car light on the dash so I’m not sure if the new keys have to be programmed and that has anything to do with it? Maybe? But I’m not sure and thank you again! I’ll post a link to a YouTube video tomorrow to show exactly what’s going on and what I’m working with for a visual!

Hello everybody, I’m really stumped on this issue I’ve been having on my 4l80e, it’s a 1989 c1500 with a 5.3 ls and 4l80e, the transmission has its own stand alone harness, it was working fine for about a year until one day the transmission did not want to shift, the trans ecu is reading tps , rpm, speed perfectly fine , the transmission is not shifting , only reverse and drive works, cannot manually shift, if I power off the trans ecu the transmission will just got into limp mode and stay in 2nd gear , I’m confused what the issue could be? Any help will be appreciated