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Curious transmission symptoms the other morning. A few details to build the context:

  • First I was the OP for this question, same vehicle...'97 Chevy Blazer, 4.3, 4wd, 257k miles on the original engine and transmission
  • About four months ago I had a shop replace a shifter/lever seal, or something like that, which seems to have stopped a slow trans fluid leak
  • I did some heavy driving over the weekend, including a fair amount of engine braking on the Blue Ridge Parkway
  • It was about time for a transmission filter/fluid change..

When I started the car Monday/yesterday morning, the following happened:

  • A stiff, heavy shudder when I shifted from park into reverse (it may be worth mentioning that I always use my parking brake, even when parked on a flat surface, which I was)
  • After backing up and shifting into gear (automatic/O), I had very low power....comparable to taking off in second gear using a manual trans
  • I noticed my "check engine" light was on
  • I pulled over, turned off the car (thinking I'd let it reset), tried to remove my key, and it was stuck..
  • Afterwards, I was able to drive it using first gear manually, so I took it to a transmission shop and left it there

After I left it at the transmission shop, they were not able to recreate the symptoms. They pulled it into the bay and the key removed normally. I theorized that I had warmed the fluid, and after sitting there, some things recalibrated and negated the symptoms. So they kept it overnight and tried it again this morning, thinking it might demonstrate the "cold" symptoms again, but it didn't.

The transmission techs think it's either an electrical or a computer/sensor-related issue. Their thinking is that it was not reasonable for EVERY part to have thrown fail codes simultaneously--literally the torque converter and every solenoid. They confirmed that my fluid was nearly perfect (I knew this as I check it almost every time I gas up) and that there were no obvious signs of trouble in the pan, such as shavings, etc.

FWIW, I experienced this once before nearly 4 years ago (the low power/2nd gear takeoff with check engine lights), however I didn't have the stuck key problem at that time. I did a trans fluid flush--crossed my fingers--and the symptoms went away until now. I've done at least two or three drain and fills since then.

Since the symptoms went back into hiding, and since it was due anyway, I had the shop replace the filter and fluid--against the recommendations of the service manager--and the vehicle has acted fine, so far. ::knocks on wood::

So the main question is....does anybody recognize these symptoms as a condition of failing sensors or perhaps disconnected/loose wiring? A secondary question is, does anyone recognize these symptoms for any other reasons that may not necessarily suggesting I need a complete transmission rebuild?


[Update 1] I found a page with a long list of symptom/solution combinations, and this one sounds very similar:

Problem: Shifts into gear harshly, car feels sluggish off the line, No 1st, 4th or Torque Converter Control (TCC) lockup available, Manual 2nd, 3rd and Reverse are only available gears, CEL is on

Symptoms: Transmission is either in limp-home mode or has lost electrical power. If there are lots of error codes in the PCM, check the under hood fuse that powers the Transmission, and if it pops again, look for a short in that circuit like an O2 sensor harness touching exhaust. Otherwise, check PCM codes for a particular fault in the Transmission causing the PCM to put it in limp-home mode.

Possible repair: Check the under hood fuse that powers the Transmission

If this is correct, I'm not sure what "under hood fuse" they're talking about. Might this be a relay? Because all the fuses I know of are under the dash on the driver side.. However a compromised circuit somewhere along the run seems very possible after 250+k rattly miles

Then again.....is it really possible this is just a bad brake light switch..?!?


[Update 2]: This guy's '06 Chevy with the same transmission, stuck in limp-home-mode even after replacing solenoids, just needed a new fuse for the transmission circuit. To summarize the useful comments:

  1. It's the BTSI (Brake Transmission Shift Interlock) fuse..

  2. Look for the trans solenoid fuse and replace with the correct number before doing anything else. Even if the fuse is not blown replace with new.

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It's been awhile since I asked this, so I wanted to leave a note that ultimately, changing the transmission fuse as discussed here seems to have worked. ::knock on wood::

At first, to test whether this approach was legit, I just swapped the transmission fuse (a red, 10 amp, if I recall) with the fuse for a different system I was less concerned about. After a few weeks of good running, I bought new fuses and replaced most everything in the fuse box, and so far it's been fine. ::knock on wood again::

In the end, this was the key insight that led me to the solution: The transmission techs think it's either an electrical or a computer/sensor-related issue. After which, Googling around I found a handful of trivial, seemingly goofy, oddball problems that can apparently have a big impact on the behavior of the transmission. These are documented as edits to my original question. But in my case, replacing the transmission fuse seems to have been the solution.

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