what's up with my Overdrive?? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 05-11-2005, 08:14 AM   #1
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Default what'* up with my Overdrive??

well i just went down to Denver today and back (~600 miles round trip). on the way down i had the gear selector in 'OD', and it seemed like i had to really press down far on the gas pedal just to make it downshift into 'D' so i could accelerate faster when passing cars, going up hills etc. so instead of pressing so far down on the gas just to downshift i began manually shifting to 'D' and then pressing on the gas pedal to accelerate. most of the time i only had to do this on hills, so i really didn't suspect a problem at this point. i just figured that'* the way it worked.

then on the way back i noticed that even with the gear selector in 'OD' the trans would not shift into overdrive unless i completely let off the gas pedal. i mean even if i maintained a steady crusie at 80mph in 'OD' in wouldn't shift out of drive & into overdrive unless i completely let go of the gas pedal. and then even if i pressed down on the gas pedal the tiniest bit, it would instantly downshift back to 'D'. also, when i completely let off the gas pedal (and thus letting it shift to overdrive) i could manually downshift to 'D' and i could feel the transmission downshift back to drive like it should. so apparantly overdrive does work, but it doesn't want to unless there is no pressure on the gas pedal

sooo.....why all of the sudden do i have no overdrive unless i'm not pressing on the gas pedal? it'* as if the computer doesn't want to use overdrive unless TPS is at 0%.

when i got into town i immediately parked and checked the trans fluid (on level ground, engine running and in Park of course). the fluid looked perfect, bright red and full. the transmission shifts perfectly fine otherwise, no wierd noises or anything.

any ideas or could this just be normal?

TIA
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Old 05-11-2005, 08:51 AM   #2
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Doesn't sound normal. I'm no tranny expert though. Soon the guys will awaken from the stupor and help out.

How many miles on the car and when was the last fluid change/filter change?
Anything odd or weird happen lately besides the tranny?
How'* the car running?
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Old 05-11-2005, 08:56 AM   #3
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the car just passed 106,000 miles (i just bought it two weeks ago). i have no idea if/when the previous owner did a transmission filter/fluid or flush.

the car runs great! although, last week when i checked mpg/hwy i got 34.7, and on this trip to Denver i only got 26.6 mpg/hwy

i really need to buy a scanner....
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Old 05-11-2005, 09:52 AM   #4
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My mother'* 95 Bucik Lesabre is the same. It'* like you gotta mash the pedal into the engine compartment sometimes to get it to downshift from 4th to 3rd when crusiing at highway speeds or up a grade. That to me sounds like crappy PCM programming. You might want to try a PCM reset so it can adapt to your driving style. The person before you (since you just bought the car) might have driven like a grandma never going over 40, so the car learns this over time and adapts. Disconnect a battery terminal for 10 minutes, connect it and drive around a day or two and see if it changes at all. Drive it how you really would drive it too.
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Old 05-11-2005, 04:45 PM   #5
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If you are at 80mph and you mash the gas to the floor will the car downshift?

The PCM uses the signal from the TPS for The trans kickdown signal and engine load...

If the TPS was dropping out, and say you were going up hill, you may have no kickdown signal and the trans may stay in OD...

On the same note if the TPS is intermintent it may keep the tranny from going to OD when it should or it could keep the TCC from being able to hit lockup...

And scantool would be a great thing for issues such as this one..

Also note, I have had issues with both of the PCM'* in my cars... And your 94 has the same PCM as my 95( 2 failed so far ) The factory unit and the reman unit...

So that scantool would be helpful in the way that it will show you what the PCM is seeing and calling for, as well as any codes that may be stored in the PCM..

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Old 05-11-2005, 07:20 PM   #6
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ugh. i took the SSE out this morning and hopped on I-90. had the gear selector in 'D' up to 75mph and then shifted into 'OD' and it went into overdrive just like it should? WTF? so apparantly now it'* back to normal!??

i hope this isn't some kind of intermittent problem i have to chase down. those are always fun

gonna buy a scan tool ASAP! thanks for the help!
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Old 05-14-2005, 06:44 PM   #7
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just wondering if anyone else here has experienced a problem like this?
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Old 08-18-2005, 12:27 AM   #8
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I am experiencing this problem and have been for several months. Seems like all the posts relating to this topic result in a self fix. Although when my scenario is repeated the results are the same; and no self fix. It'* pretty simple, yet aggrivating and now becoming expensive (with outrageous gas prices): all gears work fine upon initial driving, stop, go, fast, faster, slow; after driving for several miles (seems to be about 10 at highway speed, can be more at lower speeds) my trans shifts down into drive from overdrive; it is just as if i were to move the gear select lever into 'D' manually; and from then on out 'OD' is never accessed. This repeats if I shut the car off and let it sit and length of driving time before next misshift is proportional to length of time car sits. Any ideas?
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Old 08-18-2005, 01:21 AM   #9
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If I had to guess, I'd say you have a TPS sensor dropping out intermittantly like jr's3800 suggested. But the only way to tell is by reading the data with a scan tool or just try a new one.

Either way, get it resolved RIGHT AWAY! If you let it go too long it very likely will cause damage to the transmission, and as everyone knows, that isn't cheap!
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Old 08-18-2005, 02:19 AM   #10
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I agree with the TPS diagnosis. I'd also like to know what your Trans fluid looks and smells like.
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