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Noticed when I got a MAP sensor wiring problem repaired a couple of months ago on my '05 Colorado that there was a P0894 code in memory.. Which is basically "Generic transmission component slipping"
I cleared it, thinking it might have been a false code due to the MAP sensor problems (Wiring harness was broken, so it would intermittently think there was no MAP sensor for a second or two).. It came back.. Not enough to illuminate the MIL.. So, scheduled a time to take it to the shop, as the tranny was rebuilt about 10k miles ago and was still under warranty.
Driving down to the Atlanta area last weekend, on I-85 at about 70mph.. Felt like a kick in the butt, transmission felt like it jumped out of 4th gear to 3rd, or perhaps O/D to 4th.. Which now seems to have been the torque converter clutch disengaging.. Which seems to be a fail-safe mode for this transmission. Stop, wait a minute.. It drove fine for another 5 miles or so, then happened again and illuminated the MIL.. Fished my code scanner from the back, saw the P0894 code, cleared it.. As soon as I cleared the code, TCC (I assume) re-engaged and it ran fine the rest of the way down and back.
Got it to the shop on Tuesday.. Didn't have a code, they said they needed the code to do anything.. It was back by Wednesday, again, not enough to turn on the MIL..
They found that the "Sonnax coated pump valve" had failed or was failing and replaced it under their warranty. Only had it back for less than 50 miles, so.. No comment on whether that was 'it' or not yet.. I tend to believe them.. But time will tell. They said an updated part was just put out, so they used that one to replace it..
I did some searching on the P0894 online, and there's alot of horror stories about it.. Just thought I'd post one that, seemingly, isn't that bad. Every other post about it I saw pretty much said "rebuild"
If anyone is a tranny expert.. I'd love a low level technical explanation and whether you think their fix holds water.. It's under warranty for another 2 years/36000 miles or so.. If the code comes back, they'll have to do it again, so.. I don't see it as worthwhile for them to fudge about the problem.
So.. Apparently.. Just giving a heads up on this, again, if anyone runs into it.. The pump valve was not the only problem, if it was ever the problem.. Code came back within a few days.. They wound up replacing the entire valve body and torque converter (again, under rebuild warranty)...
Apparently, when they rebuilt it originally.. They used all the upgraded parts in rebuilding it, but an old style torque converter.. Which, the mismatch (so they say) is what was causing the code to throw.
I can say it rides a whole lot smoother after the latest round of fixes.. It's surprising what you 'get used to' so far as feel..
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