Year: 2008
Engine: 3.7L I5 Automatic
Miles: 152,303
Current DTCs: P0700, P0741, P0420 (10+ years old)

Looking for advice on how to proceed with my transmission issue. Previous pan drop and fluid change was at 121,000 miles in September 2022 so I was due for a trans fluid change. Dropped the pan and replaced the filter on August 20 and I didn't think the fluid was overly dirty either. Within the past few days, I really started to feel the RPMs jumping way up with just a slight tap of the accelerator. I could feel and hear it shifting gears driving around town but only when I accelerated slow and smooth. Quick scan showed the codes P0700 and P0741: Torque Converter Clutch (TCC) circuit performance or stuck off. I decided to drop in a bottle of Seafoam Trans Tune first since the shifting issues didn't seem awful just driving around town. I had to take a 75-mile round trip on the highway yesterday and the issue because extremely noticeable. Seemed to get through gears 1-3 "okay" but it couldn't seem to lock into 4th gear around ~70mph. Felt some surging until I either backed off the gas or stepped on it a bit more. RPMs steady around 3,000 as well. There almost seemed to be sweet spots where I could cruise at 75mph without the RPM remaining high but it didn't take much to get back to the surging.

Seems obvious what I need to do now but I'm looking for any advice on whether I should simply try to replace the single TCC solenoid that's throwing the error or if I would be better off buying the entire 4L60E transmission solenoid kit with harness. I feel like the entire harness kit would be best after reading through this TCC solenoid and P0741 thread but I just spent $300+ on a driveshaft and CV joint last month and was hoping not to have to spend another $300 for the entire kit. I will if that's the correct thing to do most of the time when this type of issue shows up but curious if anyone has just replaced a single solenoid and been fine after. Also, I'm not 100% clear on the specific individual solenoid needed, the TCC solenoid or the TCC PWM solenoid. I'm also not interested in doing any wiring. Can someone confirm that all solenoids are remove/replace with plugs? Seemed to find some conflicting info across the forums.

Worth also noting that I haven't noticed any transmission-related issues prior to this one which made me think it could have been me inadvertently screwing something up with the wiring when I had the pan off last month. I didn't notice any problems other than one of the gray plastic clips that hold the harness up seemed to be loose or broken. I didn't think it was in the way when I bolted it back up by any means but I guess it's possible that the harness was loose and got pinched between some of the other components. That seems like a stretch but I'm in an interesting spot with the trans over 150,000 miles already.

I'm plan to keep my H3 until it cannot be driven anymore but would reallllly love to avoid having to look into another transmission now.

 

I'm personally going to recommend rebuild time or swap for known good unit.

 

All the problems started when - You Dropped the pan and replaced the filter on August 20 ???

 

@ski.dive correct. It’s been in the back of my mind since it started that I could have potentially knocked something loose but dropping the pan isn’t overly complicated. I did a little bit of light cleaning before I replaced the filter and bolted it back up but nothing that I would consider as rough.

 

make sure the fiter seal is seated properly and that you dont have an old seal stuck inside behind the new one.

 

Will double check it once I drop the pan again. I removed the previous one that I installed in 2022 when I changed the fluid last month and installed the new one that came with the filter. I don't believe that I caused any damage during the seal removal or install process but I will be sure to take a close look.

 

Completely forgot to add that I've been smelling trans fluid when driving the car, especially with the A/C on. It's a pretty strong smell coming from the vents. I can also smell it right after turning off the car and getting out. Can't see any active leaks, though. Everything is dry around the pan bolts and hoses leading to the bottom of the radiator. Not sure what to think about that.

And so it's documented here, I have been checking the fluid to be sure it's still within range on the dipstick so low/dirty fluid doesn't seem to be the culprit.

 

If fluid is HOT/Boiling it will vent vapors out of the Trans Vent Hose = you can smell it. If that continues, fluid itself will blow out the vent and you will see it under the truck going toward the back. If that continues it will spew on the ground.

You are in rebuild territory if it runs too hot too long. Can you get a trans fluid temp reading with a scanner while drive at full operating temp?

 

The vent hose is definitely damp at the tip. Haven't noticed anything on the ground yet but that could be it. I went ahead and bought the AC Delco kit with the harness and got it in the mail today. I'll drive it one more time tomorrow morning and try to grab the trans temp reading. I can't seem to get the transmission temp through my code reader and apps, but I do have the Vident iLink 400 that can provide that. Although whenever I try to look through everything in that reader, all the electrical components just shut off and go dark. Never figured out if I was doing something wrong or what.

I'll remember to get the temp reading in the morning and hopefully I can drop the pan and swap out the solenoids and harness in the afternoon. I'll be sure to document what I find and add anything relevant here.

 

Good luck with the job. If you do ‘t have it already, here is the relevant FSM section for the work:

https://charm.li/Hummer/2008/H3%20L5...0and%20Repair/