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Old 02-21-2011, 11:17 PM   #1
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Default Transmission Electrical problem

1992 Bonneville lost first & second gear, transmission shop says trans is fine they can ground at the PCM and get the gears.They say everything points to the PCM but I have tried 3 different ones but always the same result no first or second gear.I have been looking at and cleaning grounds , I have printed off some All Data diagrams but I don't know what gears the A & b Selenoids control and when they need to be grounded, If anyone has any ideas I might look at to solve the problem it would be much appreciated. Thanks Dennis
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Old 02-22-2011, 01:53 AM   #2
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On the transmission plug, check that the wires haven't cracked. Sometimes that'* the issue. On my 94, the top wire broke off, and I didn't have 4th or overdrive. I soldered it back together and had the trans working again. Also, manually shift into 1st or 2nd, and you may have at least 2nd gear to start off in. Whether in 2nd or 3rd, you should go to N to idle at a stop light.
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Old 02-22-2011, 07:28 AM   #3
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With your pcm inside and the trans in the engine bay, it'* possible to have broken wiring anywhere in between. I'd start by checking for continuity from the pcm connector to the trans.
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Old 02-22-2011, 07:49 PM   #4
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It is a floor shift model no matter what forward gear you select it starts in third then shifts into overdrive normally, reverse and neutral work in their correct positions.I will check the plug at the transmission,I have cleaned the PCM grounds and checked continuity on them, their all good.I see why the trans shop says everything points to the PCM because when they ground the selenoid wires at the PCM plug the car shifts I think this proves the wires good to the trans selenoid, its like the PCM not sending the ground it has,but 3 PCM'* doing the same thing? I don't think so.I will look at the plug then I guess its to the dealer,glad its just a back up car. Thanks Dennis
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Old 02-23-2011, 07:44 AM   #5
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In 1st, both solenoids are energized. So I would back probe the solenoid ground wires @ the connector when the car is supposed to be in 1st gear and see if in fact that you are grounded. The power wire is a common wire between the shift sol. When the car shifts to 3rd, the solenoids are turned off.

You could also have a connection problem @ the computer or where the wire meets the computer connector.

I agree with the shop that the trans is not the issue.

Did you check for codes? You may see something.
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Old 02-24-2011, 08:43 AM   #6
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SGP suggested to me in the past to make a connector box to do some testing. Are you sure the shop plugged in at the computer? it'* more likely they plugged in at the trans.
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Old 02-24-2011, 09:32 AM   #7
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I would still like to see what codes are present, if any.
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Old 02-24-2011, 04:36 PM   #8
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No codes were ever set I even checked the donor PCM'* when I put them in.The trans shop was grounding at the PCM plug, and had the car running on the rack listening to it go through the gears, this would make me and them think everything from the PCM to the trans was fine.I don't know what all tells the computer that it needs to go to first gear I think maybe its not getting that message.I guess or hope to know soon broke down and dropped it of at the dealer for them to look at. Thanks I will post what they find.
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Old 03-06-2011, 03:21 PM   #9
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The dealer says electrical checks out good, they think it is a blockage in the valve body.I tried to reproduce an outside ground the solenoids to get first gear at the PCM connector with no luck.I also found the trans shop must of originally had the wrong two wires, they had a yellow VSS hi, and IACB Hi whatever that is, my diagram says it is yel/blk, and lt. green, I also confirmed 12 volts at plug into trans and ohmed all the grounds and thewires to the shift solenoids to be good.I found how to check the TPS on the forum and will try this and try to find out how to check VSS, even though there are no codes set.I will take it to a different trans shop $1,300. for rebuild but he says its not normal for the trans to be fine going to get coffee then leaving 10 minutes later with no first or second, unless there had been other signs -noises or slipping which we didn't have he says sounds electrical to him, But where?
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Old 03-06-2011, 05:28 PM   #10
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You could have a solenoid that has failed mechanically. It should, but may not set a code.
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