1997 88 LS, Code P0740 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 12-17-2011, 12:43 AM   #1
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Default 1997 88 LS, Code P0740

Hello; I'm new to the forums. I found this place while trying to find a potential solution to my problem; hoping maybe someone here can help.

About two weeks ago, there was a massive snowstorm; long story short, my car (the titular 1997 Olds 88 LS) slid into a ditch. Day of, it had to stay because there was too much snow on the ground for anyone to be able to grip the road enough to pull it out. Next day, a friend gave it his best shot, but with both of us flooring in reverse, the car slid into another ditch and snapped his tow webbing. This second ditch, however, had a much shallower approach a few hundred feet down the road; I drove it a little ways, where it got stuck on a patch of ice and had to wait another day for that to thaw.

Third day, I did finally get it out; beginning that day however (and known to have only begun that day), I no longer had reverse. Further testing showed that, above 20mph, the clutch would slip. The MIL lit for a few minutes that first day, but then never came on again until I located the TCC itself and pulled the plug, then plugged it back in. Upon obtaining a code reader, I got code P0740, TCC circuit malfunction; by that point, I'd kind of already guessed that was the case.

I'm about 80% sure this is an electrical problem based on the aforementioned MIL re-lighting upon re-seating, but also based upon this vehicle'* track record with electronic components (A/C blower, coolant fans, headlights, windshield wiper fluid jets, coolant thermostat); however, even with this knowledge, I'm not sure where to begin.

Fuse 5C is entirely intact, as is Fuse 5 in the passenger-side fuse box. I have not been able to get a running voltage reading on the TCC plug, but when the vehicle is on, there is an 11.6-volt reading to the brown wire going in. Not sure if there are any other fuses, electrical components, etc. that I might want to check, or even where they might be (I've only had this car since October). Any help would be greatly appreciated.
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Old 12-17-2011, 09:28 AM   #2
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im no trans expert but im pretty sure the tcc is a pwm signal and cant really be seen properly with a regular meter. im sure it maybe difficult but i would trace those wires back to the pcm to be sure nothing got pinched. feel along the wire the insulation sometimes doesnt have to be nicked for the wire to be bad if it got pinched hard enough.
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Old 12-17-2011, 11:26 PM   #3
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Yes, all schematics I'm seeing show the TCC as a signal entirely controlled by the PCM. I'll have to do that when it'* light out and the sky isn't falling on me. (We've been having a lot of weather up here.) Didn't really think about the possibility of a pinched wire, since the problem didn't start until it had sat on a field for a day; the ditch-slide itself did little more than ding a fender. Still, anything is possible really; might've gotten something chewed on, too.
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Old 12-22-2011, 09:06 PM   #4
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I could not find any issues with the electrical, so I cleared the code and tried to see if another would surface; I believe now that the reason the code had been generated in the first place is because I'd started it one time with the TCC plug unplugged. Certainly, that would cause a TCC circuit malfunction. :P (I will change the primary post title to reflect this.)

In the meantime, I've been trying to study this additional sound; it'* new as of the incident, and only occurs in Park, Reverse, or Neutral. It'* a sort of rhythmic mildly high-pitched sputtering sound that seems to come from the same general vicinity as the neutral start switch. Its rhythmic frequency seems tied to the engine, rather than the transmission, as when the engine is revved and the transmission isn't engaged, it speeds up, then slows back down as the engine goes back to idle. I'm wondering if it might not be a vacuum issue? Certainly, there'* a possibility that a hose got pulled loose somewhere. I understand this was the last year GM equipped this model with a transmission vacuum modulator; that seems to still be connected to the vacuum line, if it'* what I think it is, but it'* also not where the sound is coming from.

Unfortunately, I cannot seem to find much information on this; the rudimentary diagram on the radiator cover only shows so much. Does anyone have any ideas?

For the record, the closest shop is about 20 miles away, and it'* pretty much just one guy; even if I could afford to take it in just to get looked at, I really can't get it that far.
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Old 12-22-2011, 10:32 PM   #5
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I would start with dropping the trans pan and taking a look. I've seen, more then once. Pans filled with metal. The Diff on these transmissions do not do well when spinning one tire for long periods. The roll pins come apart and the diff will eat it'* self. When this happens things start to act strange. It may drive, it may not, reverse may not work. You may hear noise. As debris built up it plugs the filter and with the loss of oil pressure, the transmission starts to slip.

Here is an example of what you may find if the diff is dead.
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Old 12-23-2011, 08:49 AM   #6
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can you take the diff off without removing the trans?
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