What it means
A fault has been detected in the Brake Switch B circuit. The switch signal may be incorrect or unavailable to systems that use it.
At a glance
- Usually lights the check-engine light
How it works
Brake Switch B is a brake-pedal switch signal used by the control system to determine when the pedal is pressed. P0703 sets when the switch B circuit signal is electrically faulty or implausible, which can affect cruise-control operation and, on some vehicles, brake-light behavior.
Common causes
Most likely first.
- Faulty brake switch B
- Open or short in switch wiring
- Poor connector contact
- Misadjusted switch
Symptoms
- Check-engine light on
- Cruise control may not operate or cancel normally
- Brake lights may behave abnormally
How to diagnose it
- Check whether the brake lights illuminate and turn off reliably as the pedal is pressed and released, and note any cruise-control cancellation problem.
- Read freeze-frame data and live brake-switch states to see whether the control module recognizes the Brake Switch B signal changing with pedal movement.
- Inspect the Brake Switch B connector and wiring near the pedal for looseness, corrosion, damage, or interference with pedal movement.
- Check switch mounting and adjustment, then test its circuit and signal transitions using the manufacturer's procedure.
- If the switch and wiring test correctly, trace the circuit to the control module and verify its input before considering module failure.
Common fixes
- Adjust a mispositioned Brake Switch B so it changes state correctly with pedal movement.
- Reconnect or clean a poor switch connector contact.
- Repair an open or short in the Brake Switch B wiring.
- Replace a faulty Brake Switch B after confirming its signal does not switch correctly.
- Repair a verified fault in the receiving control-module circuit.
Can I keep driving?
Check the brake lights before driving; if they do not work reliably, do not drive in traffic until they are repaired. Even with working brake lights, cruise control may fail to cancel normally, so avoid using it until the switch circuit is fixed.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.