About two months ago, my Check Engine, ABS, and Traction Control lights started turning on simultaneously, yet intermittently. When they'd turn on, my transmission would run roughly. I drive a manual, so shifting was jerky and if I accelerated quickly and released the gas pedal, the engine would jerk as well. Most of the time, if I simply turned the car off at a red light and turned it right back on, all the lights would turn off and the vehicle would run smoothly again, making me think this was electrical. Ran the code and it indicated a faulty Brake Pedal Position Sensor. This is where I got lost. Not entirely sure how that could contribute to a jerky transmission, so wanted to see if anyone's had a similar experience and if this sounds plausible. Appreciate any thoughts/comments

 

speed sensors and brake position sensors feed into the ABS controller which along with the transmission gear selection feeds into the ECU which can cut power for safety. Generally speaking traction control does two things: uses the ABS to slow the spinning wheel down which can transfer power to the other front wheel and cuts engine performance to reduce torque. Sounds like your Tracs was running amok due to the errant signal.

 

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I could be wrong but the brake pedal sensor should only trigger the rear brake lights? If after removing, cleaning or replacing and the problem persist you can check your ABS Module.

I used this method to check mine before taking it apart and soldering all the joints on the PC board. Worked for at least 2 years till I got rid of the 98 S70 T5. I would not use the method in the link as a permanent fix as the wedge puts stress on the PC board in the Module.
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https://www.carinstructions.com/volv...70-abs-module/
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