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.
Low severity. Can I keep driving?You can keep driving, but check that the brake lights work: that part is a safety issue.
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
Most 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
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: easy
What each character of P0703 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 7: Transmission
- 03: Specific fault in that system
Frequently asked questions
Can I keep driving with code P0703?
You can keep driving, but check that the brake lights work: that part is a safety issue.
What causes code P0703?
The most common causes are: 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).
Related codes
- P0504Brake Switch A/B Correlation
- P0571Brake Switch A Circuit
- P0572Brake Switch A Circuit Low
- P0573Brake Switch A Circuit High
- P0719Brake Switch B Circuit Low
- P0724Brake Switch B Circuit High
Sources
- law.cornell.edu: 13 CCR 1968.2
- gsi.ext.gm.com: 14OBDG04 Engine Diagnostics
- gsi.ext.gm.com: 25OBDG03A
- saabwisonline.com: dtc p0703 torque converter brake switch b circuit
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.