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Hummer H3For the Hummer driver who wants the rugged look and off road capabilities of the Hummer, but in a smaller size and with a more fuel economy friendly engine.
Closing out this thread with some notes for anyone else tackling this project, along with my own experience from start to finish.
Initial Problem
On August 20, after dropping the transmission pan and draining the fluid, I started smelling transmission fluid coming through the A/C vents right after driving. Checked the codes and got P0700 and P0741 for the Torque Converter Clutch (TCC) solenoid.
Symptoms included:
Strange shift points during normal driving
RPMs flaring with light throttle input
No engagement in 4th gear (overdrive) at highway speeds — it would surge forward at ~65 mph but never fully lock in.
After digging through this forum and hummer4x4offroad, I decided against replacing just the TCC solenoid. Instead, I bought the 4L60E/4L65E/4L70E Transmission Solenoid Kit w/ Harness (2006–08, 7-pc Set, #99088) for about $323. You could replace the TCC solenoid by itself, but it's hardwired into the harness. The other solenoids are not. I am confident in my splicing/wiring abilities and there was no way I was going to try to do that in the transmission. Figured it would be much easier and worth it to replace everything while I was under there.
Replacement
Dropped the transmission pan and drained the fluid (saved it in a container to measure what came out).
Removed the pan without taking off the shift linkage or front driveshaft. Personally, I'd recommend removing the driveshaft (4 bolts, hang it with rope on the torsion bar) — it gives you way more room. My bolts were starting to round, so I left mine on.
Trans pan magnet after draining fluid (for reference)
Notes:
If you’re replacing all solenoids (including the EPC solenoid), you’ll need to remove the 1-2 accumulator (3 bolts) and lower or remove the valve body. This also lets you remove the 20-pin harness connector. This is also necessary to remove the 20-pin connector for the harness.
You don’t need to fully remove the valve body. I just backed out all the 10mm bolts and then the few 8mm bolts, which lowered it enough to pop out the EPC solenoid.
It's pretty obvious after looking back through the instructions and reading Doc's install procedure above, but in all honestly, I didn't really know what that meant. I'd never dealt with this type of repair to the transmission components before and didn't understand a ton about what I was looking at until I watched some videos and was able to look for myself. This video on the
When you go to reinstall everything – specifically the harness and EPC solenoid – make sure to follow this order:
Install the new harness connector (snaps in with 4 tabs).
Install the new EPC solenoid (connector facing down).
Line up the retainer clip and bolt EPC back in place (this one can be frustrating, good luck).
Reinstall the three bolts for the 1–2 accumulator.
Gently snug down the valve body bolts (torque later to 97 in-lbs).
You can see from this image that the EPC solenoid is in the way if you need to remove the harness from the plug.
Other solenoids were straightforward — just don’t lose the retaining clips. The clips for the TCC PWM solenoid and the 3–2 control solenoid were a pain. I ended up making my own tool by heating, flattening, and curling an old straight pick to grab them. Spent about 30 frustrating minutes trying to grab the clips with the picks I had with no luck before just MacGyvering it.
Fun surprise:
Here's where it got really wonderful for me. Around midnight (had been at it for about five hours), I laid the new harness next to the old one and realized the TCC solenoid was on the wrong side! I about lost my mind for several minutes but then realized the plastic casing around the wiring could be opened up to expose the routing, so I rerouted the TCC solenoid wiring to the other side. Not gonna lie, I thought I was toast for a few minutes, though!
OEM harness (left) compared to new AC Delco harness (right) BEFORE I rerouted the wiring to get the TCC solenoid over on the left side of the trident.
After that, everything went smoothly: torqued the valve body bolts, double-checked connections, reinstalled the filter, and bolted the pan back on. Again, I’d recommend removing the four driveshaft bolts and hanging it out of the way instead of leaving it on. It would have made some things a bit easier and go quicker when finishing it all up.
Wrap Up
After refilling with new transmission fluid (detailed earlier in the thread), I’ve since driven several hundred miles with no issues. Just make absolutely sure you add enough fluid if you are going to take this project on. Or any time you drop the transmission pan, I guess. I’m now pretty sure the codes after the initial restart, traction control warnings, and Park/shift issues came from running low on fluid after the install. Overall, this was a necessary fix but definitely wasn't a super fun project for me. Glad it seems to be okay now and I'll continue to hope that my transmission hold for a while longer now. Good luck to any other psycho who takes this on!
