Transmission

P0703 — Brake Switch B Circuit Malfunction

Severity: medium Drive with care, to a shop

What P0703 means

The control module (PCM or TCM) reads a signal from the brake pedal switch that is missing, erratic or does not match what it expects. That signal is used for the shift interlock, cruise control, torque converter lockup and shift logic. If it is wrong, the module cannot tell when the brake is applied.

Symptoms

  • Shifter will not move out of Park
  • Check Engine or transmission warning light on
  • Cruise control does not work
  • Brake lights do not work or stay on
  • Harsh or odd shifting
  • Hard starting on cars that need the brake pressed to start

Possible causes

  1. Failed or corroded brake light switch
  2. Brake switch misadjusted at the pedal
  3. Open, shorted or corroded wiring or connector near the pedal
  4. Blown brake light bulbs or fuse in the circuit
  5. Faulty relay or power supply to the switch
  6. Rarely, a failed PCM or TCM

How to diagnose

  1. Check whether the brake lights come on when you press the pedal and go off when you release it
  2. Use a scan tool to see if the brake switch status changes with the pedal
  3. Check the brake light fuse and bulbs
  4. Inspect the switch at the pedal for position, play and adjustment
  5. Inspect the connector and harness for corrosion, damage and chafing
  6. Use a multimeter to check power, ground and signal at the switch with the pedal up and down
  7. Test the wire to the module for opens and shorts
  8. If everything checks out, evaluate the PCM or TCM

Common fixes

  • Replace or properly adjust the brake switch
  • Replace blown bulbs and fuses
  • Repair the wiring and clean or replace the connector
  • Replace a faulty relay
  • Reflash or replace the module only after diagnosis confirms it

Questions and answers

Why won't my car shift out of Park with P0703?

The shift interlock relies on the brake switch signal. If the signal never arrives, the system thinks the pedal is not pressed. Check the brake lights and switch. Use the shift lock release in your owner's manual in an emergency.

Can I drive with code P0703?

For a short time, yes, if the brake lights work. If they don't, driving is unsafe because drivers behind you cannot see you braking.

Is P0703 expensive to fix?

Often the cause is an inexpensive pedal switch or an adjustment, so the repair is usually simple. Exact cost depends on the vehicle.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.