transmission fix for engine throwing code when using overdrive


Well-Known Member
Hi all,

Thought I would post this fix in case it helps anyone else. If you don't feel like reading a novel, just skip to the part with the picture. My trailblazer ext, with original transmission at about 260,000 miles, started acting up on me. Drive around town, everything fine and dandy. Pull out on the expressway, where the speed limit is 65 mph, and sure enough after a few minutes the check engine light would light up. Pull the codes, I get a generic transmission code, I don't remember exactly what, but it was something like P0894, and in the end it meant, "transmission component slipping". Reset the codes, everything fine until the next time I went out on the highway. I started experimenting and noticed that if I put the transmission in 3rd gear, I was far less likely to get that code. But, it would still appear on occasion, but at least I could drive to work without throwing a frigging code. At some point, I started getting another generic transmission code as well, but nothing that was specific. But going up on the expressway and using overdrive was definitely a reproducible trigger.

I spent a lot of time figuring this out, what a pain. Old tired transmission, right? Who knows what it could be, bad torque converter, seals, wtf. Some other symptoms that I had:
1) hard shifting would randomly happen from 1 to 2 or 2 to 3. Typically first thing in the morning going slowly. This has happened for years, like 7 years!, but again just random and not really on a regular basis.
2) at high rpms, I swear I could hear a slight whining coming from the transmission, this has also happened a few years, but not as long as the hard shifts.

I have dropped the pan and changed my transmission filter and oil every year for years, and did this as well. Fluid looked like it always does, a little used, but no metal shavings or anything bad like that. Could not think of anything recent that changed to cause this, other than pulling a 3500 lb boat and trailer more often.

So I broke down and bought a transgo transmission kit, the one that includes the torque converter valve replacement to fix shifting issues. First thing I did was took off the valve body, cleaned it all out and put that valve in. I looked at everything I removed, and it all looked ok, no cracks, broken things, etc. Right before I was about to start drilling holes for the kit, I decided screw this, I'm putting it all back on and just trying this valve replacement first. My thinking at the time was, nothing looks broken or wrong, and I really don't want to drill holes and make things worse. At least go step by step. Put everything back together, I think the valve body itself has like 24 bolts, and filled it up with fluid and tested things out. I noticed some improved shifting, maybe? But other than that the exact same problems surfaced, much to my dismay. I'm actually pricing used transmissions on the internet out in my moments of frustration.

Then I stumble accross a tsb talking about this: #08-07-30-008B, which lists several causes for P0894, among which is a crack in the torque converter clutch solenoid. This thing can be replaced without pulling off the valve body, just an FYI. I had the old style, brown, which is prone to cracking, see picture below:


See the tiny crack I circled in red? Right next to the normal "seam" ? You cannot see this unless you pull off that solenoid, clean it up, and take a close look. It's not easy with 50 year old eyes. Rockauto sells replacements for these, you have to splice them in, but it's pretty easy to do and has the splices included, for like $20...

I put this thing in, and all my problems were solved. Not only did the engine code problem disappear, but so did the occasional hard shifts, and even the whining transmission. I suspect what was happening, was that when the transmission oil got warm enough, and enough pressure was generated, it started slipping out of that crack. Oh yeah, the vehicle has more power now as well, just runs better, for several months now. I'll bet I dropped the pan at least 4 times working on this, and got tranmission fluid in my hair, eyes, mouth, garage floor, you name it through the course of this thing. First time I ever took off a valve body as well, which as you know the first time you change something on these vehicles can be an adventure! Anyway, it's a novel but in case some search terms show up for some random Joe trying to solve a generic transmission problem. Oh yeah, here is the tsb:


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Good check.

When I first ran into P1870 issues on my old 4L60E, first thing I did was change that solenoid. In my case, it wasn't the problem, and the Transgo kit was the fix. But, hey, look at it this way - your installation of your Transgo kit can only have helped your transmission, so it wasn't all in vain. I would have been ready to turn it into a boat anchor though had I gone through the install and found it was still acting up!


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Excellent detective work, and easy enough, compared to the 'Full Transgo', that I need to remember this first, when people start asking about P187x codes. Although the splicing needs to be done; that may scare off some folks. Are the wire colors the same, old > new ?

Thanks for uploading the TSB, as well.

If we had a 'posting of the month' (hint, hint, mods), I'd nominate this one.

PS: I didn't consider the post overly long. I speak with some authority, here :laugh:


Well-Known Member
I had a moment of hope, but it seems to be no different and still throws P0894 in OD. No signs of cracking on the TCC...I believe it's the newer revision. A positive note, a new filter and a partial flush. :ugh:



Well-Known Member
Yeah I remember reading the brown one was the older version and prone to cracking. It was probably worth replacing anyway since it's cheap enough.

Although the splicing needs to be done; that may scare off some folks. Are the wire colors the same, old > new ?
I don't remember the color matching, but I remember checking the wiring diagram to make sure I had it right, you don't want to fill everything back up and tear it out again. I was fully prepared to splice my own wires with my own connecters, solder etc but the kit had everything in it and was very easy to do.

Here is the 2nd tsb, which talks about the brown vs lighter color solenoid. Note it's my year vehicle 2006 that this primary occurs in apparently.


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Well-Known Member
I don't remember the color matching, but I remember checking the wiring diagram to make sure I had it right, you don't want to fill everything back up and tear it out again.
You can say that again. The original had a black and brown wire. I took that as ground and power respectively. The replacement (non-GM) had black and red wiring. Made the same assumption and soldered them in. Worked fine. build date was 05/2017 for my Trailblazer. That 3 months past the last TSB date.....safely into the new revision part. Sad that GM never quite sorted things out with the 4L60e even with constant revisions.

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