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Old 03-16-2007, 10:54 PM   #1
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Default Another tranny/overdrive/P1870 question

I have a 96 Bonneville with 266,000 miles on it. As far as I know, this is the original tranny. The other day I had a check engine light and it was a P18709 (component slippage). I checked the fluid and it was burnt. I drained it and added Mobil synthetic and some Lucas tranny fix. I then borrowed a snap-on scan tool and gathered some info.

When the car is in third gear, the TCC appears to lock up. I say that because the scan tool shows only + and - 14 or so rpms of slippage. If I move the selector up to OD, I do not see the tack drop, and the TCC slippage jumps up to the 600 to 700 RPM range. If I move it back to third, the slippage will retrun to 0 or so. The tach moves very little during this time.

Any Ideas?
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Old 03-17-2007, 10:30 AM   #2
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Based on the above info, I would think it is better for me to not try to use overdrive. What do you think?

Has anyone lost forth gear and still had the torque converter lock-up? I can move the shifter back and forth between D and OD and see very little tach movement. And when it is in forth gear, I don't notice the engine flaring up or anything.

Oh yea, I see I spelled tach wrong and added a 9 on the end of my trouble code. It should of read P1870. I was pretty tired when I posted that and I think I was dozing off while typing.

Thanks in advance.
Andy in Mich
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Old 03-17-2007, 11:22 PM   #3
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Burnt fluid is not a good sign. If you keep it out of overdrive, it may help for a while if the issue is with the TCC, but either way it sounds like the tranny is on 'er way out.

Correct me if I'm wrong, but I think the TCC will still engage in third gear.

Drive on 'er for about a week. Then check the fluid again. Smell it. Does it still smell like it'* burning? Usually a clutch issue in that case.

With that many miles on it, and the fluid being burnt, I'd start looking for another tranny.
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Old 03-18-2007, 12:49 PM   #4
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Sounds a bit like the 4th gear clutch pack may be gone...

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Old 03-18-2007, 03:53 PM   #5
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Thanks for the replies. The TC is locking up in third according the the snap-on tester. If I slide it up into 4th gear, the tcc slippage goes up, but the tach does not due much. If anything it increases by about 100 RPM or so. I did not look at the tester for this info.

When it is in 4th, it does not seem to flare up at all. If the 4th gear clutches are gone, which I am sure is possible, would the car just act as if it was in 3rd gear. With the 4th gear clutches gone, would it just "pass through" and act as though it was in 3rd.

I have taken (2) 250 mile trips this week while leaving the selector in 3rd and it ran good except for the MPG (low 20'* instead of mid to upper 20'*).

Leaving it in 3rd and taking the trips, I did not set the P1870 code again.

Is it better to leave it in 3rd (less heat maybe) than 4th?

Thanks
andy
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Old 03-18-2007, 04:47 PM   #6
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That would tell me that you have an issue with 4th gear... Keep in mind I am not a tranny expert..

But here is whats happening... When all of the conditions are met the PCM will command the TCC solenoid on to send the TCC into lock up mode... When this happens the amount of slip between the input shaft and output is close to if not 0-10 Rpms of slip..

Now when you get to 4th gear and the PCM commands the TCC to apply you should again drop to 0-10 Rpms of slip... Even 60, 70 or 80 rpms of slip should not send the PCM into a frenzy...

I am taking a guess that its very possible that there is an issue with 4th gear, and being that you set the 1870 code in 4th gear, the PCM had commanded the TCC to lock via the TCC Solenoid and the result was not desirable according to the PCM programming... Hence the 1870 code...

Have you had a trans shop check it out?

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Old 03-20-2007, 07:36 AM   #7
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Thanks again for your replies.

To answer your question about the trans shop, no I have not talked to one yet. My experience with them is that no matter what is wrong, a complete rebuild will fix it.
I dont think it would matter if it was laying on the ground or doing what mine is doing, it will still cost like 1200 bucks or better to fix it.

With all the miles I have on my car, Im not sure if I want to put that much into it or not. I am thinking that I will just drive it using D instead of OD and see how long it lasts. I was wondering if I will get less heat in the tranny that way. The new fluid has about 6 to 700 miles on it and it is not burnt yet.

Thanks again
Andy
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