Need help evaluating problem with 4L60E

Discussion in 'Transmission & Driveline Topics' started by falloutboy, Feb 18, 2011.

  1. Hi Folks,
    a friend of mine has a prob with a 4L60E in a '99 4WD Tahoe. I have some particular question about the VCM and the shift logic/pattern behind the 1-2 Shift Solenoid Valve

    I would bother JakeShoe with this prob, but I dont know if he'd feel comfortable with e-mailing back and forth.
    Do we have another Guru for Trannies?
  2. jakeshoe

    jakeshoe Veteran Member Lifetime Gold Member

    Dec 8, 2000
    Republic of Texas
    1-2 or A solenoid is on in 1st and 4th.
  3. mrvedit

    mrvedit Veteran Member

    Jun 12, 2009
    Ann Arbor, MI
    While some people call them the 1-2 Shift and 2-3 Shift solenoids, that is actually confusing and therefore many others refer to them simply as solenoids A and B. Here are how the solenoids are engaged in the 4 speeds:

    1st Gear - Solenoid A is ON Solenoid B is ON
    2nd Gear - Solenoid A is OFF Solenoid B is ON
    3rd Gear - Solenoid A is OFF Solenoid B is OFF
    4th Gear - Solenoid A is ON Solenoid B is OFF

    The solenoids are cheap ($15) and trivial to replace. However if they burn out the computer should generate a DTC code. I suspect the computer/trans will go into "limp mode" and not shift at all if a solenoid burns out.

    There is also a "pressure switch assembly" which tell the computer the actual gear the trans is in based on the gear shift position and any "override decisions" the trans may have made. Again a cheap and trivial part to replace. I realize you are in Germany, but this is GM's most popular transmission.

    While I am barely a trans novice, you could mention what the symptoms are.
  4. Thanks for the fast answers :)

    I have never driven the car itself, can only rely on descriptions of the owner.
    The car has around 200k KM down, and the trans has been rebuilt by a "professional" (possibly a bad sign here in Germany). The PO suspected a "electrical problem"

    I guessed that one of the solenoids went bad, but I wanna go sure and check everything else, so I get every possible error the tranny might have before I tell the owner what to get and what to do.

    Car drives, but seems to shift from first directly into 4th.
    DTC P0751 Solenoid A

    Now my question is, can I test the solenoid itself via "jumper" cables? I assume that 1-2SS doesnt get the ground signal via the VCM, cause it stay i the ON possition -> hence the 1 to 4 shift. But why doesnt the VCM give the signal to ground? Or why wont the solenoid ground?

    Under what condition can I check the connector 1020 for the 12V (meaning, does the tranny still has to be installed? Has the valve body to be installed? or what else? Has the shifter be in a definite position? )
    When do I have to expect the switched ground?
    What else could I do, to exclude the VCM from the error list?

    Can the soleniod be tested if uninstalled?

    Are these test worth anything, except checking the windings? Or that the solenoid is isolated?

    About the shift pattern.
    What would occur if 1-2SS stays OFF the whole time (being grounded whole time) Do I only have 2nd and 3rd - or if 2-3SS is OFF only 3rd?

    Can you describe the "pressure switch assembly" more in detail? Or what its official name is? (so I can look it up in my eSI)

    Thanks - my real pro's :)

    P.S.: talking about eSI, how can I find just wiring diagrams in it? I just stumble over them from time to time, but cant find only diagram.
  5. mrvedit

    mrvedit Veteran Member

    Jun 12, 2009
    Ann Arbor, MI
    OK. P0751 indicates that the transmission is shifting unexpectedly from 1 to 4 and that a likely cause is Solenoid A. While you could try to "poke" into the wiring to diagnose the solenoid, I wouldn't recommend it. If you apply ground or +12 to the wrong wire, you could fry the ECM (computer).
    Instead drop the trans oil pan and simply disconnect the solenoids and test them with an ohm meter. They should test at around 20-40 ohms. If you really wanted to, you could jumper 12V and ground to them to ensure they "snap" and move their plunger. (Make sure they are disconnected from the trans harness before testing!)

    With the oil pan off, you can remove a solenoid in 10 seconds - pull down/out retaining clip and pull out (sideways) solenoid. Note the Solenoid B is spring loaded with a very mild spring.

    If a solenoid is bad, it is trivial to replace.
    If the solenoids are good, you have an electrical problem. Either a short, an open or the ECM is faulty and can no longer pull the solenoid circuit to ground.

    I'll try to find some schematics for you later. I have many printed out, but the websites are either gone, or I don't know where I got them.

    You absolutely do not need to drop the entire trans or even the valve body to diagnose and likely fix all this.

    The "Pressure Switch" is also called the "pressure switch manifold". 'llI find a picture for you, but it sounds like it is OK from what you have said so far.
    Last edited: Feb 18, 2011
  6. mrvedit

    mrvedit Veteran Member

    Jun 12, 2009
    Ann Arbor, MI
    Here is a wiring diagram:

    While Solenoid A is always Pin A on the trans connector, it will vary widely as to what pin this is on the VCM or ECM.
    On a 1999 Camaro, it is circuit 1222, Light Green wire which connects to the PCM red connector pin 48. On your truck it is likely something very different.

    Here are some other 4l60E diagrams:

    If you find that the solenoids are good, you will have to debug the electrical circuit. It could be:
    1. The solenoid wasn't connected.
    2. The Pin A wire in the trans harness got pinched and grounded.
    3. Pin A is broken on the trans connector
    4. The VCM/ECU can no longer pull circuit 1222 to ground.

    If you end up thinking it is 4. let me know and I will give you some ideas on how to test that. I don't check the forum all the time, but my email that I check hourly is:
    ted -at- vedit -dot- com.
  7. mrvedit

    mrvedit Veteran Member

    Jun 12, 2009
    Ann Arbor, MI
    Not sure this info will help you, but to be complete...

    A good Scan tool, like what a professional trans shop should have, can activate any solenoid without the engine running, e.g. with the trans pan removed for easy access to the solenoids.
    For example, with my HP Tuners scanner, I can, in an absolutely quiet garage, actually hear each solenoid engage and disengage. (Even with the trans pan on.)
  8. Thanks for all the help.
    Now I'll have to wait what my friend finds out.
  9. Hi, got some news:
    Solenoid 1-2 : 26,4 ohms; hooked up to 12V - works fine.
    solenoid 2-3: 26,2 ohm
    3-2 contoll solenoid: 26,2 ohms
    TCC PWM solenoid: 15,1 ohm

    So solenoid 1-2 or as u call it solenoid A seems to work fine.

    I assume the VCM doesnt support the ground signal for the solenoid.
    But HOW do I check this, WITHOUT a Tech2 or other tester? (except a Multimeter)

    I am kinda at a loss here. :(
  10. mrvedit

    mrvedit Veteran Member

    Jun 12, 2009
    Ann Arbor, MI
    I don't have the experience to say exactly what it is, but here are my thoughts:
    * It appears that Solenoid A (1-2 shift) is not turning OFF, it is staying ON. (Therefore some of my previous comments don't seem valid now.)
    * I would first remove Solenoid A again from the valve body and verify that it is under spring tension. If there is no spring tension, it won't turn off. (Note that Solenoid B does not have spring tension; Solenoid A is more in the middle of the valve body.) Since you say the trans was rebuilt, I would guess this is likely.

    I can think of several reasons why Solenoid A won't electrically turn off:
    * It's wire is pinched and grounded in the trans case. It is Pin A on the trans connector. This is also somewhat likely.
    You could test this by removing the harness connector from the trans and checking the resistance between Solenoid A terminals and the case. If the Pin-A terminal is less than 25 ohms (it might even be infinite) there is a short inside the trans. It should be easy to check the wiring inside the trans.

    * The VCM has a fault and has the corresponding line internally shorted to ground. (The line will be run by a power transistor in the VCM and when they fail, they often short out.) If the trans was simply rebuilt, this seems less likely. You might be able to test this by connecting the trans harness again and disconnecting the battery. Then check the resistance between the Solenoid A Pin-A terminal and ground(case); if it is now less than 24 ohms, it may be a defective VCM. I don't know how to be sure without determining which VCM wire it is and cutting it.

    If it were me, I would first check that Solenoid A is spring loaded and if OK, drive it to a GM dealer that has transmission diagnostic equipment.

    BTW - If you put the rear axle on jack stands, start the car and put it in gear it should try to shift to 2nd gear at just 11mph. (With a stock tune, the trans is programmed to shift to 2nd gear with minimum throttle at 11mph.)

    Again, please remember that I am a novice with this and am just trying to help.

    BTW - There is a nice series of Youtube videos on the 4l60E valve body. Here is one of them:

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