P0504 Brake Switch A/B Correlation

What does P0504 Brake Switch A/B Correlation mean?

The P0504 Brake Switch A/B Correlation code is a generic powertrain code that applies to OBD-II equipped vehicles.

This code is set by the vehicle's powertrain control module (PCM) when it detects a failure in the brake light circuit.

The brake switch is responsible for turning on and off the brake lights when the pedal is pressed and released.

If there is a malfunction in the switch, it can result in the brake lights either staying illuminated continuously or failing to illuminate at all.

This can lead to hazardous situations on the road.

The most common cause of this code is a faulty brake light switch, which can be easily replaced.

It is important to address this issue as soon as possible to ensure safe braking and proper functionality of other related systems.

Troubleshooting P0504 error code

1. Check brake lights by cycling them on and off and ensuring the bulbs are good
2. Check voltage on the red wire of the brake light switch connector with a voltmeter
3. If no voltage, check wiring to the fuse block
4. If voltage exists at the white wire with the pedal extended, replace the switch
5. If switch is adjustable, check the adjustment
6. If brake lights function properly but the code still persists, check remaining wires on the brake light switch
7. Probe remaining wires for power and replace the connector
8. Backprobe the wire adjacent to the power wire with the pedal depressed
9. If there is no power, replace the switch
10. If power is present, the problem may be in the wiring to the computer or with the computer itself
11. Backprobe STP terminal on the computer to ground and check for voltage
12. If 12 volts is displayed, replace the computer
13. If little or no voltage, replace or repair the harness from the computer to the switch

See other p05 OBD Codes

OBD Trouble Codes Ranges