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Thread: 4L80E tranny headache

  1. #1
    Junior Member
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    Sep 2010
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    4L80E tranny headache

    So... I traded two P.O.S.'s for a slightly polished ****. I knew when I bought it that it had a problem with the tranny but I was hoping it was just dirty. It is not that simple. I've spent the past two month (on and off) trying to get the tranny out of "limp" mode with no success.

    Here's what I have:
    '95 Chevy 2WD Dually with a 7.4L and a 4L80E tranny.

    Here are my symptoms:
    Will only shift between 2nd & 3rd but has reverse.

    Problems revealed with an engine analyzer:
    Bad MAP sensor - swapped.
    Bad spark control module - swapped.
    Bad Quad driver module
    Bad ABS wheel sensor - checked and found section that feels like it was pinched (heading to the junkyard for a replacement).

    Other work/testing I've done:
    Could not find a downshift module for a 4L80E only a 4L60E. Changed the filter and shift solenoids. Checked for fluid on the tranny harness connector and it is leaking so the internal harness will need to be swapped, in the mean time I cleaned the connector with brake clean, blew it out with air and put dielectric grease in the contacts. Swapped the input speed and output speed sensors. I've checked the TPS and pulled the IAC and cleaned it (the code for the ABS is the same as the code for the IAC). Tightened all electrical connections to the bat. Swappped the ignition switch harness with a junkyard unit. Checked all fuses. Pulled an ECM from a junkyard van to test and this did not change the symptoms. Pulled out the meter and test light and started testing pins at the ECM and the tranny plug, I have bat & ign power to both.

    My questions:
    Will a faulty ABS sensor cable cause the tranny to go into "limp" mode?
    When testing the pins with the ignition on I have 14.5 VDC on the 1-2 Sol. and 245 mVDC on the 2-3 Sol. does the ECM need to see certain perameters before it will allow the 2-3 to work? This is a ground switched unit.

    I know I'm not listing some of the symptoms I've found but I can't think of anymore right now. I'm certain this issue is electrical but I'm not familiar enough with the system to know what steps to take next. I've been using the Haynes manual and the ATSG Tranny manual and have checked everything they have recommended.

    Something else... this has a OBDI system in it. The only code I have found manually is on the ABS side. I had a local parts house hook a scanner up and it did not flash any codes. I took it to a local shop and they hooked up a Snap-on computer and found the codes for the sensors and modules.

    Any help I can get would be greatly appreciated.

    Thanks!
    '95 C3.5K 2wd Dually, 7.4L, 4L80E, Stock 4 now :sleepy:.

  2. #2
    Senior Member
    Join Date
    Sep 2008
    Posts
    206
    not to be the berrer of bad tiddings but I spent months going thru the same frustrating steps to find out that the crank didnt slid all of the way into the transmission the motor spun the flat spot off of the pump. you can get a brand new 4l80e from GM with the factory warranty for around 1800. I still have a good core if you are interested. these have a 700. core charge

  3. #3
    Junior Member
    Join Date
    Sep 2010
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    I came here to post a very similar issue. If you feel I am thread******* I will start a separate one.

    I don't think the faulty ABS sensor will cause the tranny to go into limp mode. My front left sensor has been faulty for several months with no tranny issues. Although my tranny is just now acting up.

    From the research I've done the past couple days, the solenoids are hooked up in parallel with Pin E (the 12 VDC supply from the fuse block). You should see at least 12 VDC on both of those as well as the TCC solenoid.

    I have a '96 C2500, with a 5.7L and 4L80E.

    It appears to be stuck in only 3rd gear. If I start off with the gear selector in 2nd and manually shift to 3rd and OD, it will shift to 3rd and sometimes OD. I have 12 VDC at the tranny in off and run, but it drops to ~9.5 VDC in start. That sounds low to me, but "limp" mode would put the tranny in 2nd, not 3rd. I haven't hooked up a computer to it yet, but I have started looking into the sensors and solenoids. When I applied a voltage to the solenoids (Pins A-E and B-E), I could hear the 1-2 solenoid cycle, but not the 2-3 solenoid. I did a resistance check across the same pins and got 22 ohms each. For the TCC solenoid (Pins S-E) I got 11 ohms. I forgot to check the pressure control solenoid (Pins C-D). I have no idea what the acceptable range is for these components. I'm planning on checking these again when I get the chance just to double check it.

    Currently, I'm leaning towards a bad 2-3 solenoid that's stuck in the "on" position. Is there anything else I can check before I drop the pan?

  4. #4
    Junior Member
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    Sep 2010
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    Hey, the more the merrier as long as it fixes our problems.

    A couple of quick things about what you have done and found.

    Yes you should have 12VDC to Pin E in OFF and RUN but only with the ignition in the START and RUN positions not in OFF or ACC. I'm not sure if you already know or not but the tranny is ground switched so as long as you have 12VDC where you are supposed to in the tranny the problem is more than likely a grounding issue.

    I haven't checked on mine to see what kind of voltage drop I get at startup but if you feel you're getting too much you may want to check your battery it may be starting to get weak.

    As far as what to check before pulling the pan I would check and test the engine temp sensor, TPS and MAP sensor since these are all tied into the grounding of the PCM. I've also read that some people have traced a problem to a bad ignition switch harness.

    Hopefully some of this will help. I know you've given me a couple more ideas to try. I'm hoping to work on it some more this weekend so I'll keep you posted.
    '95 C3.5K 2wd Dually, 7.4L, 4L80E, Stock 4 now :sleepy:.

  5. #5
    Junior Member
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    Sep 2010
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    Apparently I can't find what I'm looking for, but once I switch to something else I find what I was looking for the first time.

    Solenoids A and B 20-44 ohms
    PCS Solenoid 3.5-8 ohms
    TCC Solenoid 10-15 ohms

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