2020 579 peterbilt with paccar engine. Brake lights causing engine to not build boost

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Weking, Jan 20, 2021.

  1. Weking

    Weking Bobtail Member

    Jan 20, 2021
    I drive a 2020 579 Peterbilt and ever time I touch the foot brake or hand brake the lights come on and stay on which causes the engine to build no boost. The shop has replaced the light switch and brake pedal valve and problem still there. They are planning on changing the TC valve tomorrow. Can someone please help? The brakes have zero pressure on the gauge when this problem occurs so I am leaning electrical. If anyone else has had this problem what fixed it?
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