03 4T65E slipping in 1st - Page 4 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 10-05-2010, 11:30 AM   #31
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Quote:
Originally Posted by BillBoost37 View Post
I have a local guy with that code, have read the fsm many times, consulted with Steve and Dave etc etc.

P0748 is a pcs electrical issue code. You need to check the wires from the pcm to the connector at the trans for continuity. Then ohm out the wires at the trans connector and see what readings you get. At about 190F, IIRC the reading should be 6-8 ohms.

With this code set, your pressure should be maxed out. This is the reason why you are getting ..."firm" shifts.
Yep, sounds like we're on the right track. Worst case I'll run two new sets of wires and figure out the wiring harness later, but this sure as hell sounds a lot easier than dropping the subframe and taking the pan off. Lets hope it really is that easy because I want to be able to drive this car to California starting Friday night, and I still have to drop the gas tank to replace the fuel pump, replace the two front coilover springs (which actually only takes 10 minutes), and get an alignment.

Thank you all for your excellent help so far. I'll keep you all posted.
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Old 10-05-2010, 11:49 AM   #32
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That'* what the FSM says. PCM, wiring or soleniod. Currently I'm chasing something with this code on my buddies car and it'* not magically fixing itself. Pisses me off. We've done all of the above.

If you have to drop it.. holler and I'll give you the tips/tricks.
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Old 10-05-2010, 02:25 PM   #33
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Does anyone here happen to have the pinout diagram of what I need to verify? I know Bob re-pinned the PCM as this swap required him to do a few interesting things, but I'd really apprecaite it if someone could provide me with some diagrams to help me out. Which wires do I need to test for continuity on the pcm and on the trans connector?

Bob gave me this information earlier, but I'd just like to verify that its correct. This is for a 2003 transmission, and a 99 Monte Carlo PCM.
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Old 10-05-2010, 02:41 PM   #34
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I know I have the pin out for the trans at home. I might have put it in tech info under transmissions. But I don't recall.
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Old 10-05-2010, 02:45 PM   #35
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you know i haz access to them.

99 MC:


03 Century:

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Old 10-05-2010, 02:57 PM   #36
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Yep, that would be it.
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Old 10-05-2010, 03:04 PM   #37
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Anyone have one for the 99 MC PCM? I need to know where those wires go in order to test them, lol. I have the pin numbers written down at home, but it helps a lot to see the diagram. Like these for example, I wouldn't have been able to figure out since I would have had A-D reversed.

Thanks again!
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Old 10-06-2010, 11:18 PM   #38
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Alright, I've made some small amount of progress.

1st gear continues to slip regardless, if you drive it normally. However, if you manually shift into 1st, you will feel the car downshift (and engine brake) into 1st at 10mph. That'* what the tune is set to downshift at. If you then accelerate with the shifter in 1st, you have a perfect gear. I made a blistering fast run to 80mph that way just earlier. Everything is perfect. However, everything fails the moment you forget to downshift into 1st as you're slowing down.

I already checked the PCS wiring to the PCM, and that'* just fine, and I also checked the resistance of the PCS, and that'* also within spec. I haven't yet tested terminals D and C for shorts inside the transmission harness, but I will be able to tomorrow when I get some light tomorrow.

So what do I do? I have HPTuners and I've been playing around with the settings all night but haven't found anything that would make a difference.

Given that everything works perfectly when I keep the shifter downshifted into 1st gear, I'm led to believe that this is not a problem with the transmission, but rather a problem with the tune or the PCM. I am using a 99 PCM after all.

Any help would be greatly appreciated.
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Old 10-07-2010, 07:35 AM   #39
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By pulling down manually into 1 or 2 you are engaging an additional band known as the manual 1-2 band. This adds more grip. ..
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Old 10-07-2010, 10:36 AM   #40
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I keep thinking the problem is the shift accumulator. The 1-2 piston may have a bad Oring causing pressure to leak past the piston. It'* a easy task to drop the pan and inspect the accumulator. As Bill pointed out, manual shift is a different band. So this tells me the 1-2 band is not engaging right.
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