Closed Throttle Switch A/T

Discussion in 'Technical' started by tjleilo, Apr 27, 2019.

  1. tjleilo

    tjleilo New Member

    I found out why my automatic transmission slows down very quickly if I release the gas pedal after I reach 64kmh (40mph). Around that speed is when my torque converter locks up. I have a new throttle position sensor set at .46V and the closed throttle sensor also works. Though, while the transmission can see how open the throttle is and reads it as a percentage through cozult, it doesn’t read when the closed throttle sensor is on or off.

    My ECU can see the closed throttle sensor and when I let off the pedal the closed throttle sensor turns on as it should and it does what it should, though, the transmission doesn’t turn it on, and that keeps the torque converter engaged.
    Does anyone know why it would do this?

    I know what it says to do in the manual and I have already checked the the harness where it plugs into the TCU and made sure the plug is sitting in the TCU correctly. Again, the sensor is working and the transmission is reading the TPS but isn’t turning on the closed throttle sensor...but the ECU is and reads it just fine...?

    My transmission fluid temp sensors voltage isn’t correct and is wrong as well, just a side note. I don’t think that would correlate with this, but who knows.
    At idle the transmission reads my TPS opened at 0-1% it switches back and fourth very fast from 0-1% but it never engages the closed throttle sensor.

    TWIN TERROR Well-Known Member

    Are you sure you have the correct throttle position sensor/switch as there are different ones for different models.
    Just a thought
  3. tjleilo

    tjleilo New Member

    Yeah, this issue was here before I changed it out. Good idea though. I hope I can get this fixed...
  4. LitlElvis

    LitlElvis Z32 Servant

    It seems like the problem would be either with the TCU or the lock-up solenoid in the transmission. Check if the TCU turns off the voltage to the circuit when it should... if there's voltage at all times, it's the TCU - if there's only voltage when expected, then the solenoid is most likely stuck open.
  5. tjleilo

    tjleilo New Member

    Thanks! I think it isn’t stuck open. Could a bad ground wire in the TCU harness cause this too? I can feel it when it clicks over and locks up around 40mph. It’s weird. Thanks!
  6. LitlElvis

    LitlElvis Z32 Servant

    I believe the lock-up circuit is powered by the TCU and grounded inside the transmission at the solenoid, so I don't think a ground wire in the harness would affect it.

    Does the lock-up disengage at all when braking to a stop? Or does it stall the engine? I tend to think the engine would stall when the car is stopped if the lock-up did not disengage.

    You also mentioned that your transmission temp sensor voltage is not correct - I'm only guessing here, but I think the lock-up function would be limited by the transmission fluid temperature. The transmission needs to get up to operating temperature as quickly as possible for best efficiency and allowing the converter to lock-up when cold would make the transmission take longer to get to operating temp. Your temp sensor's incorrect voltage may be part of the problem but I don't think it would keep the lock-up engaged indefinitely.
  7. tjleilo

    tjleilo New Member

    Ohhh that makes sense...
    The lock up does disengage at 39mph (62kph) when I let off the throttle, but if I’m going any faster than that it will be locked up. The car doesn’t stall. The transmission always thinks that it’s hotter than it is, so it thinks it’s at operating temperature really quickly after starting up, and even when the voltage is wrong (the voltage is always out of range at the sensor) but for a short period after starting up it will show that it is at its operating temperature (it will not actually be at its operating temperature, it would be colder in reality but the car thinks that it is at operating temperature despite the voltage being off at the sensor) but it will still not lock up correctly either way.
    Thank you for your help! Hopefully this can get figured out!

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