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HELP! needed for troubleshooting

This is a discussion on HELP! needed for troubleshooting within the Computer & Tuning forums, part of the LSx Technical Help Section category; So I finally rebuilt the tranny and engine. everything hooked up and the engine starts the very first time. after ...

  1. #1
    Junior Member 98goldta's Avatar
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    gold
    1998 trans am

    Question HELP! needed for troubleshooting

    So I finally rebuilt the tranny and engine. everything hooked up and the engine starts the very first time. after i take it for a spin using autotap i get the codes p1810 and p0748. these are transmission switch and pressure control circuit in the tranny. the troubleshooting leads me to believe the trans. range switch is not working correctly( I didnt replace this part). Upon further logging I see that the reason p1810 is flagged is when i am driving the car the pcm sees it in park/neutral. 1st reads first, 2nd reads 2nd, 3rd reads 2nd , drive reads park, reverse jumps in and out of park and reverse, neutral and park , read correct. also in the tranny the transmission input and output speeds dont register. on the throttle the idle air counts are not reading. So the question is does everyone think the tranny is the problem or is it the pcm starting to go flakey. I have checked the wire harness for all these signals and the continuity is good. the grounds on all the pcm pins are solid. Also one more item to note is with autotap i can not read the freeze frame data for the codes. it looses communication everytime i try to read them. it checks the dtc's just fine though.
    so what do you all think? sorry for the long read. and thanks for your help in advance.
    1998 Gold T/A 1 of 235 built, 3.08 moser 12 bolt, k&n filter, TB mod, egr mod, Lingenfelter 3.5" alum ds, Pcv oil catch can, BMR Lca's, Bilstein HD Shocks, Poly Sway Bar bushings, Full Ram Air Hood, optima red top, 220000 +miles ,never been to track Currently motor and tranny being rebuilt

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    Moderator Cutlass's Avatar
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    its hard to imagine all those things being related unless there really is something wrong with the PCM, power and/or ground to the PCM or your Autotap is flaky. You could try another scan tool for the IAC counts, Freeze Frame, and trans ISS and OSS.
    As for code P1810, that sounds like it could be a bad Trans Fluid Pressure Switch. There's even a service bulletin for it. Maybe start there, clear the codes and see where that gets you.

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    TunedbyFrost.com Tuner Frost's Avatar
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    Make sure all of the harness related to the shifter in the console is hooked up.

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    Member Tampa Tuning's Avatar
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  5. #5
    Junior Member 98goldta's Avatar
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    gold
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    Frost
    thanks for the advice. I didnt mess with anything on the console, but i will take a look and see.
    tampa tuning
    I live in Bartow.
    cutlass
    as for trying another scan software , i have auto tap on 2 different laptops and both read the same. when i unpluged the IAC with the car running nothing happens, and the voltage on the wire to ground on the 2 outer pins reads .485 volts . the 2 inside pins read 12.5 volts each. the coil reads 48 ohms on each pair of pins. does this seem wrong or are they inline, i dont have anything to go by for specs. is there a way to jumper the coil with a battery to see if the plug moves in either direction. i suppose the IAC could be faild along with the tranny range switch.


    thanks for the help guys, I will keep testing.

  6. #6
    Junior Member 98goldta's Avatar
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    gold
    1998 trans am

    Thumbs up

    Well, i took apart the console and no loose wires. put it back together started up the car. i played with the shifter several times from reverse to drive and 1st 2nd and 3rd. at one point i got autotap to read that i was in 4th gear but when i selected neutral and back it would not repeat. when i left it in drive , with it reading correctly after a few minutes it would jump to park and of course the idle would change as if the computer thought it was in park. so it looks like a bad switch. to confirm that it wasnt the pcm, because the IAC is still not reading on autotap, once i shut the car off i removed the IAC servo and with my finger pushed the plunger in. I turned the ignition to on, and the servo moved all the way out and back in to the parked position, so i am assuming the pcm is controlling this correctly i just cant see it with autotap for some reason.. so i guess i am going to pull the pan and replace the switch, wish me luck.
    Last edited by 98goldta; 01-15-2011 at 02:22 PM. Reason: signiture did not post

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    Junior Member 98goldta's Avatar
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    gold
    1998 trans am

    Smile

    just so every knows the switch was completely sscrewed up, open and close resistances were all over the place. purchased a new one and installed. everyhting related to the range indication is now working. still troubleshooting other issues still.
    thanks everyone for the advice.

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