Solenoid question, please help!

Discussion in 'The Projects Forum' started by dmc0162, Apr 28, 2008.

  1. dmc0162

    Thread Starter Active Member

    Dec 13, 2007
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    Alright well I need to do something for a solenoid inside my transmission and I was hoping somebody could help me.


    This solenoid is inside of my transmission and it controls the hydraulic pressure bypass valve. I 100% no longer need this solenoid to function, so I want to disconnect it.

    The problem is, if I just cut the wire going to this solenoid from my engine computer, the engine would see this as a fault in the circuit, and it would go into a "safe mode" and cause a check engine light.

    The solenoid operates on 12v, and has a resistance of 3 ohms. How can I "trick" the engine computer into thinking that the solenoid is still there when I cut the wire in half? People have told me that all I need is a resistor on the engine computer side of the wire, and then ground it. Is this true?


    Basically, I need to cut the wire going to the solenoid so that it gets no power, but make the engine computer still think there is a connection. Any ideas?

    Here is a picture to help you understand:

    [​IMG]


    Thanks in advance, guys!
     
  2. Caveman

    Active Member

    Apr 15, 2008
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    If I understand you correctly the resistor would work.
     
  3. dmc0162

    Thread Starter Active Member

    Dec 13, 2007
    51
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    What kind of resistor? Just a 3 ohm resistor? What about the watt rating?
     
  4. Caveman

    Active Member

    Apr 15, 2008
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    Well... 3 ohms. And the power is V^2/R = 144/3 = 48Watt.
    Hmm... that's a whopper!
    Remember that it just has to trick it enough. I would actually test it with larger resistance values and see what you can get away with. Maybe 100 ohms, 2Watt. Then just drop the resistance to get it to work.
     
  5. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,687
    900
    There is a possibility that the engine computer senses the resistance without putting very much current/voltage to the solenoid. At least, not until it tries to activate it. By analogy, the airbags in my car need a 2-ohm resistance on each plug or an error signal is created. Current is quite low, until it tries to set them off.

    Do you know under what conditions the computer will be sending a signal to the tranny? If there was a way to interrupt that signal (assuming you have not already stopped it), then there is a good chance that a fairly small wattage resistor, say 3 ohm at 2W, would keep the computer from detecting a fault. If you cannot interrupt the signal, then I would test drive whatever you use to be sure it does not get too hot as the control unit tries to operate the solenoid. John
     
  6. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    50 Watt 3 Ohm resistors can be had for two to ten bucks each. DigiKey has them, as does Newark and Mouser.
     
  7. dmc0162

    Thread Starter Active Member

    Dec 13, 2007
    51
    1
    Could someone please give me a link to a 50 watt 3 ohm resistor on Mouser or Newark? I just tried finding one but I am having a little trouble. Thanks
     
  8. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Seems to me that the signal to the solenoid is a series of pulses around 70 to 120Hz. The computer is likely expecting to "see" an inductive load; when a pulse hits the coil it initally looks like an open circuit until the current starts flowing. However, the current is cut off before the coil goes into saturation. The static resistance may very well be 3 Ohms, but the impedance at the frequency and duty cycle of the driving signal is something else altogether. It might be best to just leave the solenoid connected, unless you can use a decent O-scope on it and figure out what the actual impedance is.
     
  9. Caveman

    Active Member

    Apr 15, 2008
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    Search at mouser.com for
    resistor 50W 3ohms
     
  10. Externet

    AAC Fanatic!

    Nov 29, 2005
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    Hi.
    I will venture to say that your schematic is incomplete; in series with the solenoid could be a switch that closes to ground when the transmission reaches 4th gear.

    Substituting the solenoid with a resistor/light bulb/solenoid outside the transmission, MAY tell the ECU the transmission is all time in 4th gear as the same ECU senses ground when not energizing the line, probable spitting an error code anyway.
    I may be wrong as you do not specify car/transmission/model/year... Is that the TCC solenoid or other ?
    Miguel
     
  11. thingmaker3

    Retired Moderator

    May 16, 2005
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  12. dmc0162

    Thread Starter Active Member

    Dec 13, 2007
    51
    1

    There is no switch in series with the solenoid. This solenoid does not change gears, it simply bypasses fluid pressure all the time to provide softer shifts. It is perfectly ok to disable this solenoid, I just need to know how without casuing the computer to see a malfunction in the circuit.
     
  13. dmc0162

    Thread Starter Active Member

    Dec 13, 2007
    51
    1
  14. techroomt

    Senior Member

    May 19, 2004
    198
    1
    or, you could go to a junk yard and pick up a (good) used one, and connect it to the wiring normally connected to the one in the engine. strap it up somewhere out of the way.
     
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