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What does p0504 brake switch A/B correlation mean?

2 Answers

DiWyatt

07/28/25 8:18pm

p0504 brake switch A/B correlation means there is an issue with the quality of the brake switch itself. Below is an introduction to the related content: 1. Causes: Aging, poor connection, short circuit in the brake switch circuit, or aging/overload of electrical appliances connected to the brake switch output, such as brake light bulbs. 2. Function: The brake switch transmits braking information in the form of electrical signals to the ECU to determine whether the brake is pressed, control the vehicle speed, and also serves as a crucial basis for stopping cruise control and disengaging the torque converter. Therefore, the brake plays a significant role. The reason for the fault code is that the ECU detects incorrect correlation between the brake pedal switch and brake pedal position switch signals, water-induced short circuit in the brake switch, poor contact of the brake switch, damage to the brake switch, or faults in related circuits.

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DiIsabella

08/12/25 1:06am

My last car had a P0504 code, and it felt like there was something wrong with the brake switch. It means the signals A and B from the brake pedal switch didn't match up. This switch controls the brake lights' on/off state and also affects the cruise control and auto start-stop system. Possible causes include worn or stuck contacts inside the switch, or loose/dirty wiring connections. The system triggers an alarm when it detects inconsistent signals. Ignoring it could lead to the most annoying issue—brake lights not turning on or off, increasing the risk of rear-end collisions. The start-stop function might also act up. I tried checking it myself: start the engine, press the brake pedal, and have someone check the taillights' response. If the lights aren't responsive, the switch needs replacement. Don't delay—use an OBD scanner to read the fault details or take it straight to the repair shop. Replacing the switch usually costs around a hundred bucks, and regular maintenance like cleaning dust near the pedal can prevent recurring issues.

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