What does p0504 brake switch A/B correlation mean?
4 Answers
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.
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.
As a long-time car owner, I'm quite familiar with the P0504 fault code – it indicates conflicting brake switch signals. When you press the brake pedal, the switch should consistently send signals to the ECU, but detection points A and B are giving contradictory readings. Possible causes include worn internal components of the switch or corroded wiring harness contacts due to moisture exposure. This directly affects brake light operation – either keeping them permanently illuminated (distracting following vehicles) or causing start-stop system failures. Safety first – my friend nearly had an accident because of this. The diagnostic procedure is straightforward: turn the ignition on (without starting engine), repeatedly press the brake pedal while observing dashboard light changes, then confirm with a scan tool. For repair, either clean the switch or replace it. I recommend having technicians verify proper switch positioning during routine maintenance to prevent future issues.
P0504 code indicates a brake switch signal mismatch. The switch is located near the brake pedal, and when pressed, it activates the rear red lights. If there are two signal points A and B, the system detects they are not synchronized. Possible causes include a faulty switch or poor wiring connection. This issue may result in abnormal brake light operation, which is dangerous as other drivers won't recognize your braking. A simple self-check method: start the engine and press the brake pedal while having someone observe if the rear lights respond; if abnormal, avoid DIY repairs and visit a mechanic promptly. The typical solution is replacing the switch.
