Q: Hydraulic brake booster warning light and buzzer will sound after car has been sitting in extreme cold. Turns off after car warms 2004 Lexus LX470

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The car had been outside all day (Chicago winter) and as we began driving home, the break light came on and a buzzer began to sound. It did not come on until about 5minutes or so into driving time. We pulled over and pulled and turned off emergency break, turned car off and on. None of these things helped. Breaks were functioning normally so we continued driving. After about 10 minutes or so, the buzzer stopped and the light went off. The next morning, this did not happen again but, the car had been in our garage overnight. When my husband got into his car at the end of the day, after the car had been sitting exposed at the train station all day, it happened again. Same thing yesterday. Fine in the morning after being in the garage overnight, but buzzer and light in the evening after sitting at the train station. The breaks feel normal (no stiffness etc). It is bitterly cold here right now with consistent temps and wind chills below zero.

Hi there - the brake booster, which also incorporates the high pressure brake pump for the anti-skid brakes, may have an electronic controller with a failing circuit board. This kind of failure behaves in the manner you describe - heat sensitive - and gradually worsens over time and miles. It may or may not be possible to replace the boost pump controller with a rebuilt unit (or rebuild yours). I would recommend a brake system inspection by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, give you an accurate assessment of damage and cost estimate for repairs.

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