Powertrain, generic · Transmission

P0703 Brake Switch B Circuit

Check engine lightOn
EmissionsNot relevant
Drive cycleRequired
Limp modeNo

Brake switch A is usually the brake light switch, B a second, redundant contact or signal used to cancel cruise control, release the converter clutch, check 'brake before throttle' and for stop-start. Since about 2014 GM receives it as a CAN message from the body module and checks its integrity (rolling counter, protection value: 3 of 10 faulty in 2014, 9 of 17 in 2025) without the check engine light; cruise control is disabled. Subaru-based systems (Saab 9-2X) check the circuit electrically during stops and starts and light the MIL after two trips. An NHTSA investigation of Hyundai and Kia brake light switches lists P0703 with a brake light that stays on. Brake switch A codes are P0571–P0573, disagreement between A and B is P0504.

Likely causes

Brake light or double switch worn, corroded or misadjusted
Wiring or connector at the pedal damaged, fuse blown
CAN message from the body module disturbed (GM: software, bus fault)
Aftermarket LED lamps or trailer module distorting the circuit

Symptoms

  • Cruise control cannot be engaged or drops out
  • Brake light stays on or does not work
  • Selector cannot be moved out of P (shift lock)
  • Check engine light depending on the maker

Repair estimate

DifficultyEasyDIY possible
Parts and labour€20–150
Time0.3–1 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

brake switchbrake switch wiringbody control module

Related codes

P0504P0571P0572P0573P0719P0724

References: law.cornell.edu, gsi.ext.gm.com, gsi.ext.gm.com, saabwisonline.com.