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  1. #1
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    Default TCC issues, or a gremlin?

    Howdy all!

    Long time lurker, first time poster. Got a 2008 Grand Prix 3.8L N/A base from my brother who passed away a few years ago. Believe it or not, it was on a lift in a tranny shop when he died, it got stuck in a parking lot and was towed to said shop the day before. I had called him that afternoon when I found out, and was supposed to hear back that night with details, but got a call from the paramedics on his phone instead. **Hug those you love often, you never know when your "last time" to see them will be**

    Anywho, that shop was not very confidence-inspiring and wanted $2500 to overhaul the transmission, and with everything else to deal with, I just found a used one for I think $600 with 37K miles and had them put that one in. Car had just under 100K at the time, and that was about 50K miles ago. Other than telling me to pull over due to the tranny overheating one time (like 265 degrees!), I really haven't had any trouble out of either. About 10K miles ago, I installed an aux cooler, and after dropping the pan, changing fluid/filter and back-flushing the lines, finally got the heat to stay under 190, even on the interstate in summer. I was a happy camper!

    Jump to about two weeks ago, it started slightly raising rpms like 300 or so cruising on a flat highway at about 65 MPH, then back down, then would repeat after 30 seconds or so. When I got to a slower, more curvey and hilly stretch of road, it was more pronounced, so I put the selector in 3 to keep it more steady (and disengaged cruise). Checked the fluid as soon as I got home, was at the low end of the good range, so I added about a pint and called it a night. Next day, took it for a test run, no change. Hit the internet and saw WAY too many possible 'causes' for this, figured out the quickest and easiest thing to try would be to pull the PCM fuses for an hour or so to reset. Another test drive and it was worse! Now it 'bucked' a few times, too, mostly under slight throttle up a hill around 40-45 MPH. Backing off or pushing on the throttle would stop it. Harder throttle it wouldn't do it. OK, read some more about cleaning MAF and TB, also about some saying pulling negative battery cable like overnight, so I did the latter and planned on getting cleaner the next day. No change (except for a something weird I'll bring up later), even after the cleanings. Went on another (longer) trip to town to get/try some injector cleaner, and it wasn't really bucking anymore, but I had now seemed to loose either 4th or the TC completely! Read some more on average speeds for shift changes, went on another test drive to determine if it was 4th or TCC, and now I have a DTC - P0741! All of this has occurred within 150 miles or so.

    Now for the weird part. Right after I started driving it years ago, I had that headlight issue where low beams would just go out, frantic flipping switches and flashing brights would bring it back, but there's not much scarier than driving down a curvy country road at night and having your lights go out! So, I replaced the headlamp relay/module (in the fuse box) and that fixed it. Except it did it again a couple of times on me about 1 week before this shifting weirdness started. Also, after pulling the two PCM fuses for an hour, the headlights went out completely, daytime running lights and all, and no flipping of switches would bring them back. Great! Well, after I pulled the negative cable overnight (see above), they are back on, operating normally! One more electrical weirdness happened a couple of hours ago. I had read earlier about pulling the main tranny harness under the TB to remove all signals, leaving R, 2nd and 3rd with full line pressure, and thought I'd try that a little to see if I could maybe free up the TCC or PCS with the added pressure, got in the car, closed the door, put the key in the ignition, and the doors locked!! I'm not kidding! I went ahead and turned the key to ON, waited for the fuel to pressurize (like I always do), turned the crank and all dash lights just went out. Turned the key to off pretty quickly, and watched all the guage needles do their little peg dance!!! With the dash as dark as night!!! Thought "well that didn't go well", unlocked the doors and proceeded to plug that connector back in. Got back in, started right up, just as normal as you please. OK, I'm going crazy, this didn't just happen, so I pulled the connector again, tried to start, and the exact same thing happened again, plug it back in, starts right up.....

    for the , but I'm hoping someone can tell me I'm not !!!


    Where do I go from here?!? Lucas Trans Oil? Transgo Shift Kit? dealer PCM reflash? Crazy house? My brother really loved this car, and so do I, so hopefully one of you gurus can help me out!
    2008 Grand Prix Base 3.8L V6 - bone stock (well, a trans cooler! )

  2. #2
    GT Level Member wstefan20's Avatar
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    Default Re: TCC issues, or a gremlin?

    As far as the last section goes, your instrument panel data is tied directly into your transmission data, so it's feasible that by having this unplugged it caused the instrument panel module to "wig out". I wouldn't be alarmed by this result.

    For the rest however, a bit more serious! This by far takes the cake on strange electrical problems I've heard of!

    It's hard to tell without looking at direct shift data or being there in person, but I would wager that your issues are unrelated to anything you did. I'm leaning more towards an issue with the TCC solenoid or the natorious TCC valve in your valve body. It's possible it's an electrical issue though, but your headlight issue could be unrelated so it's hard to say. The high heat could have caused internal problems in the transmission, etc.

    Basically, if I were you, I'd run to a real transmission shop to run a diagnostic procedure on it and see what they unearth. Though it might be beneficial to try upgrading your pcm (zzp, intense, overkill etc.). There's so many things it could be, it's really hard to say. Sorry I haven't been much help! I wish you luck though. Sorry to hear about your brother.

  3. #3
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    Default Re: TCC issues, or a gremlin?

    Thanks for the reply and good words. I wish I had a more advanced scan tool, but the one I have basically only reads and resets DTCs, no live data streams. The fluid on the dipstick looks pink and doesn't smell horrible like it did before, but I know those years of driving with excessive heat could have done some damage. I've only had bad experiences with tranny shops in the past, and generally like to do everything myself, but I might have to bite the bullet. Would/could a GM dealer be able to scan the tranny and check the PCM? I've seen some say they will scan for free, charge for a reflash, but some say they charge if you walk in the door! Guess that's up to each dealer...

    If it's the TCC valve or solenoid, would a little Lucas make it better? I guess it couldn't hurt, huh? I've looked for bad wiring, loose connections, cracked vacuum lines, etc. but haven't seen anything obvious. I did recently change the plugs and wires, and I used the technique of rotating the motor forward to access the rear plugs, but this was after I was already having trouble with the shifting. I had replaced the (easy) front plugs and wires a couple of months ago, and put off the rears 'cause of the PITA factor! I sorta thought the shifting weirdness might have been because I was still running with one bank of old plugs / wires. No change after replacing them, however.

    I'm a little concerned about driving it anymore, but you gotta do what you gotta do... I've seen several posts of people who have chased a similar problem for months or years, so I guess it shouldn't leave me on the road any time soon. I do have roadside towing on my insurance! I did see info on driving with a bad TCC, like it dumps lots of metal into the fluid everytime it has a problem, is there an easy way to disconnect or disable it until I get it figured out? TIA!
    2008 Grand Prix Base 3.8L V6 - bone stock (well, a trans cooler! )

  4. #4
    GT Level Member Gregorius's Avatar
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    Lightbulb Re: TCC issues, or a gremlin?

    Well, you are probably crazy, but with that being said....


    1) Weak Battery. How old is it? What do the clamps look like?

    2) Bad grounds. Battery ground, harness grounds. There are about a dozen places on a GP where a ground wire is is bolted to the frame with a 10mm bolt. They all corrode, lose connection and cause gremlins. Take em off, wire brush the eyelets and bolts, sandpaper the body/frame, coat everything in dialectic grease, reassemble. I say this all the time, but I've fixed too many issues by cleaning electrical crap up. There is a list of them floating around here somewhere.. Hmm. There it is.

    Magic Link to WarStryker13's google drive

    http://drive.google.com/drive/folder...nN3SVBBWmlkTnc

    3)I guess the Slippy OD issue could be electrical... or a fluid pressure issue<Bad PCS/TCC?>. But I assume the 4th gear clutch is shot. PITA.
    Magic Link to WarStryker13's Google drive


    ... our lady of blessed exceleration, don't fail me now ...

  5. #5
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    Default Re: TCC issues, or a gremlin?

    Thanks for the reply, and the link - good info there!

    The battery is good, pretty fresh, like a year or so old. Connections are clean, no corrosion, although the neg is snug, it could be tighter. I just brightened them up a bit, and we'll see if I can get that adjustment screw to turn on the neg terminal!

    I'll go through your info pages and check out the ground locations, couldn't hurt! I'm leary of tranny shops, but I've seen some good reviews on one not too far that says they do free computer scan and road test, I guess I'll give them a try, probably tomorrow. I think I'm also going to try some Lucas...
    2008 Grand Prix Base 3.8L V6 - bone stock (well, a trans cooler! )

  6. #6
    GT Level Member wstefan20's Avatar
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    Default Re: TCC issues, or a gremlin?

    Wish I could give better news. Sometimes switching from dex 3 to dex 6 and a shift kit will help some, but especially with 4th clutch there's nothing to do other than a rebuild.

    On a brighter note, you don't have to be a master tech to tackle these transmissions. I have rebuilt three of these so far and all are still running. Never touched a transmission in my life before that first one! Only spent $500 on parts and rebuilt everything from case bushings, seals, electronics, 4th clutch, steels and frictions, bushings, tcc valve, afl valve and all! Only need one special tool, some time, the free astg manual, $30 ebay video manual, and tears! First one took all weekend, now only a few hours!

  7. #7
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    Default Re: TCC issues, or a gremlin?

    I'm with the having a shop look it over. Had a bad coil that didn't throw a misfire, but caused some nice high load, low rpm issues. Similar to what you describe, tough to say though. I swapped the trans (cause I'm that guy) and still had the issue. Decided to shotgun a bunch of parts (had everything laying around) and located the coil issue.

  8. #8
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    Default Re: TCC issues, or a gremlin?

    I might have to take a look at those coils. I did retrace some stuff today, cleaned and put penetrox on the battery terminals, and on that main ground connection right below the neg terminal. Weird thing, when I removed that ground, nothing happened, but after brightening and coating, upon reattaching got a pretty healthy spark - even the horn sounded off a little! Also strange, without starting it up but key on, the DIC was reporting 12.24V, so I hooked up my charger, took a couple of hours to reach 100% (at 4A charge rate). Afterwards, checked DIC again, and with just the door open and ignition on (nothing else) watched the volts go 12.5 to 12.4 to 12.3 in like 5 seconds! OK, so the battery (replaced Jan/16) isn't that great, had it tested at walmart, showed 630 CCA, and 12.66 - PASS! ?!?

    I had also decided to spray some QD cleaner on that 20 pin connector at the top of the tranny under the TB, and also rigged an elbow on that vacuum line that bypasses the TB (had a crack at the base of the plenum end), and on the way to have the battery tested (like an hour drive one way) hardly a sniffle out of the trans!?!?! I mean, it was almost like before all this started, just a couple times did the TC seem to loose lock. I'm really hoping this does turn out to be some weird electrical problem, although a PITA to chase down, MUCH cheaper in the long run! I'm going to spray the harness side of that connector tomorrow, and I noticed there's another identical one at the top of the driver's side strut tower, gonna hit that one too. Pretty sure I've seen a procedure to test the coils, so may have to do that, too! Keep the good ideas coming folks!

    Oh, yeah, the low beams went totally south tonight, luckily I'm under the 150k extended warranty on these - this will be the second time I've had to change out this part! Gonna take a trip to the dealer tomorrow, I think...
    2008 Grand Prix Base 3.8L V6 - bone stock (well, a trans cooler! )

  9. #9
    GT Level Member wstefan20's Avatar
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    Default Re: TCC issues, or a gremlin?

    strange... hopefully that's it! Let us know! I'm invested now! haha

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