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1994 Silverado 1500 4x4 - Shifting Problem 1st to 2nd

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by Papi325i, Mar 7, 2009.

  1. Papi325i

    Papi325i New Member

    Hello everyone,

    I have a 94 Silverado 1500 4x4. It's running great, expect the truck seems not to know when to shift out of 1st. I have to lift off the accelerator in order to get it to shift; if I don't, it starts to get into red-line territory. The rest of the gears shift fine. Anything simple that anyone thinks can sooth this, if not make it go away? I appreciate the input.

    Rudy
  2. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    Hi Rudy,

    The PCM tells the transmission when to shift. The PCM is watching Throttle Position, Air Flow, and Vehicle Speed to determine when to send the signal. So a faulty speed sensor, TPS or dirty Air Flow Sensor can Cause your problem. I would check for codes if possible. This will give you the correct place to start your diagnosis.

    If you don't have a scanner the first thing I would do is clean the Mass Airflow Sensor which is located between the Air Cleaner and the Throttle Body. Use BrakeKleen or Denatured Alcohol to clean the sensor. HTH
  3. ct9a

    ct9a Epic Member 5+ Years 1000 Posts

    Actually, if it's a '94 I don't think you need a scanner. You just have to jump the ports on the diagnostics port by your left knee. Also, if your '94 is like mine, you have a TBI 5.7L, which mine doesn't have a MAF sensor, but a MAP sensor instead.
  4. Chris Miller

    Chris Miller Rockstar 100 Posts

    That's easy to do. Take a paper clip and jump the top right-hand terminals on the computer plug(it's next to the parking brake release), and put the key in Run(DON'T START IT). The light will blink out the code 12. That's the diagnostic. After it blinks that code three times, any fault codes will follow. If none are present(and on some early 94s, they didn't program in any transmission fault codes), I'd suspect the 1-2 shift solenoid on the side of the transmission.
    Last edited: Mar 8, 2009
  5. Papi325i

    Papi325i New Member

    No Codes on Jump / AAMCO Says Tear Down Needed

    Thanks for the imput guys. I jumped the code port and no codes came up; it just kept blinking the "12" code. I took the truck to AAMCO for a free diagnostic, and lo and behold they want me to pay $700 to tear it down. Then they'll tell me what's wrong from there. Am I being too cynical, or should I feel this is what they tell everyone?

    One of you mentioned a selenoid on the side of the tranny. Where is it and is there a way to check if it's bad? I haven't had time to find and see if the aforementioned sensors (TPS, MAF or MAP, Etc) are dirty or what not. Again, is there a way to test those?

    Clearly I would prefer to avoid forking over all that money to AAMCO or anyone if there's a way to narrow down the problem myself. Thanks again guys for the imput.

    Rudy
  6. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    Rudy,

    You can check sensors till you're blue in the face and you probably wont find a bad one. I would take the truck to someone with a scanner that can see your trucks data <sensors in operation> . Drive the truck watching the scanner to find the sensor that is acting up. A sensor that is giving the computer bad information may never set a code. A good example is a Speed sensor that's reading too slow because of dirt on the pick up. The computer will see this slow speed and believe it. The result is your truck won't shift until 20MPH. The same analogy can be made with the air flow sensor. Make sense?

    Jim
  7. Papi325i

    Papi325i New Member

    I'll definitely try to find someone that's willing to do that. Thanks a lot. And if anyone out there knows some one in Los Angeles, by all means give me a heads up.
  8. Papi325i

    Papi325i New Member

    Well, after checking out other posts and people with similar problems, I'm gonna go for a 1-2 shift solenoid change. It doesn't seem horribly difficult to do it yourself, so if anyone knows of a good DIY guide, that would be appreciated. I'll check out a Haynes book to see if I'm up for it, and if not, it seems like only a few hundred dollar job. I'm willing to take that chance before spending thousands on a remand or used tranny job.
  9. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    Why not attach a Snap On scanner and test the solenoid first? You can switch the solenoid on and off with the scanner and see if it works. If this solenoid "SSA" were bad your transmission would take off in second gear shift to 3rd and not shift to 4th.
    If the other Solenoid "SSB" were bad your transmission would take off in 4th and shift back to 3rd.
    If you have all 4 gears both of your solenoids are working.
    Instead of looking for a quick fix to try why not find the problem first before wasting your money on parts you don't need?
  10. Papi325i

    Papi325i New Member

    I'll try to find a scanner, but a lot I'm seeing work on newer models (96 and newer). My truck's a 94 and I can't seem to find a specific scanner (not just code reader) that works on it. If anyone knows a specific one, I'd like the heads up (Snap On makes a lot of differnet ones it seems).

    With the way the truck shifts, all I can tell is the following:
    - Reverse Works
    - When I manually select 1, it works.
    - Nothing happens when I shift over to 2, regardless of throttle position
    - When I shift to D, it'll shift if I drive slow or let off the throttle a bit
    - Overdrive seems to do something when coasting; if I coast and shift back to D, the RPMs will go up

    But, I'll head to the store to try to find a scanner that'll work on a 94.

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