DTC Troubleshooting: P0504 (159)
  1. Measure voltage between brake pedal position switch 4P connector terminal No. 1 and body ground.
Is there battery voltage?
YES -
Go to Step 16 .
NO -
Go to Step 15 .
  1. Check the No. 21 HORN, STOP (15 A) fuse in the under-hood fuse/relay box.
Is the fuse OK?
YES -
Repair open in the wire between the brake pedal position switch and the No. 21 HORN, STOP (15 A) fuse, then go to Step 29 .
NO -
Repair short in the wire between the brake pedal position switch and No. 21 HORN, STOP (15 A). Also replace the No. 21 HORN, STOP (15 A), then go to Step 29 .
  1. Turn the ignition switch OFF, and wait 2 minutes.
  1. Disconnect ECM connector No. 2 (58P).