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2003 cavalier trac off/ jumpy tach/ hard shift

So I just got this '03 cavalier 2.2 a few months ago, and its really been a dream car for performance. Any way, last week, just driving normally in traffic, the trac off light came on and the tranny started shifting hard between gears. I pulled over and shut off and restarted the car. the light went out and shifting returned to somewhat normal. I never got nor have i gotten yet a check engine light. now the trac light comes on intermittently, and returns to shifting hard until i restart the car. if i baby it, it will stay off for short trips. it may have been acting funny befor the trac light came on, but now that i'm paying attention, i notice that between 2nd and 3rd with the trac light off, the engine seems to rev and the tach will jump just as it changes gears. 4th gear on the highway will kind of flutter and downshift too easily, almost on its own. 1st to 2nd seems fine as does 3rd to 4th. I did some research and tried changing the TPS, and it didn't work. this seems like a shot in the dark considering I'm not getting a code. I already had my mechanic put the reader on and there's nothing stored in the computer. Thoughts?


  • A bad Vehicle Speed Sensor (VSS) is a possibility.
  • is that the same as a wheel speed sensor (WSS). the one thats in the bearing hub.

  • Nope!
    You probably have two VSS, and they are connected to the Transmission Control Module, the Engine Control Module, and to the speedometer. Whether they are internal to the transmission or are external, I don't know, but some other forum members will know that info.
  • should this throw a code? or is this a maybe/maybe not situation?

  • Yes, it should throw a code, but...

  • You're describing a transmission that is slipping. And if the transmission starts to slip it will go into what is called the limp mode. When in the limp mode, the TRAC light will come on because the transmission is malfunctioning. If the transmission is slipping the tach will be erratic especially between shifts. And finally, when the transmission goes into the limp mode, the ECU will raise the line pressures within the transmission to prevent further damage. And this is what causes the rough/hard shifts.

    Have you checked the level/condition of the transmission fluid?

  • Ive had plenty of experience with slippy transmissions. It just doesnt feel that way. It has to be electrical. The trans feels fine.
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