P0703: Brake Switch B Circuit (Meaning, Causes, Fixes)
What P0703 means
The brake pedal switch does two jobs: it turns on the brake lights and it tells the computer the pedal is pressed. OBD-Codes.com explains that on automatic transmissions the powertrain control module (PCM) uses this signal to release torque converter lockup (the clutch that locks the engine to the transmission at cruising speed) before the car slows to a stop, otherwise the engine would stall. It describes P0703 as a generic code (it lists Ford, Honda, Mazda, Mercedes and VW among examples) that sets when the PCM detects a malfunction in the brake switch circuit designated B, applies only to automatic transmissions, and notes that some vehicles have more than one brake switch. RepairPal defines P0703 more simply as Brake Switch B Circuit, set when the PCM sees an implausible signal from the brake switch. The sources differ on emphasis: OBD-Codes.com names the code Torque Converter/Brake Switch B Circuit Malfunction and focuses on torque converter lockup, stalling and transmission damage, while RepairPal lists brake lights and cruise control as the symptoms and doesn't mention the torque converter. Related codes are P0700 (transmission control system MIL request), P0702 (transmission control system electrical), P0740 (torque converter clutch circuit) and P0571 to P0573 (cruise control/brake switch A).
Severity: can I keep driving?
Stop and fix promptly
Get it fixed right away. OBD-Codes.com says P0703 should be treated as urgent because severe internal transmission damage can result if torque converter lockup stays inoperable for a long time. RepairPal rates P0703 Urgent. Both sources say your brake lights may not work, so check them before driving: a car whose brake lights don't come on is much more likely to be rear-ended.
Common symptoms
- Brake lights don't come on (both sources)
- Cruise control won't work (RepairPal)
- Engine stalls as the car rolls to a stop (OBD-Codes.com)
- Torque converter lockup disabled, lower fuel economy and weaker highway performance (OBD-Codes.com)
- Erratic shift patterns or limp-in mode (OBD-Codes.com)
Likely causes
Roughly most to least common, based on the sources below. Your vehicle may differ.
- Failed brake switch (both sources)
- Misadjusted brake switch, which OBD-Codes.com says is often misdiagnosed as a failed one (OBD-Codes.com)
- Open or shorted wiring or connectors in the brake switch B circuit (both sources)
- Blown fuse or burnt fusible link (OBD-Codes.com)
- Faulty PCM or a PCM programming error (both sources)
Diagnostic steps you can do
Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.
- Have someone watch the brake lights while you press the pedal. If they don't come on, fix that first, since it is a safety problem on its own.
- Check for technical service bulletins (TSBs) for your vehicle, since the problem may be a known issue with a known fix.
- Visually inspect the brake light switch above the pedal, its connector and the brake lamp wiring, and check that the switch is adjusted so the pedal arm actually presses it.
- Test the stop lamp fuses, including with the brake pedal pressed. OBD-Codes.com notes a fuse can look fine but fail once the circuit is under load.
- Read and write down all stored codes and freeze frame data, clear them, and test drive to see if P0703 comes right back.
- With a digital volt/ohmmeter and a service manual, check for battery voltage at the switch input, then at the switch output with the pedal pressed. No output voltage points to a bad or misadjusted switch, per OBD-Codes.com.
Typical fixes
- Readjust the brake light switch
- Replace the brake light switch
- Replace a blown fuse and find what caused it to blow
- Repair open or shorted wiring or connectors in the brake switch circuit
- Reprogram or replace the PCM only after the switch, fuses and wiring check out
Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.
🛠 When to call a pro
- The brake lights still don't work after replacing the fuse or switch
- The engine stalls when you come to a stop
- The transmission shifts erratically or stays in limp mode
- You don't have a meter or wiring diagram to trace the circuit
Where to buy
Plain search links. Always match parts to your exact year, make, model and engine.
FAQs
Is P0703 the brake light switch?
Usually. Both sources list a failed brake switch as a cause, and OBD-Codes.com adds that a misadjusted switch is often mistaken for a bad one, so check the adjustment and fuses too.
Is it safe to drive with P0703?
Not for long. RepairPal rates it Urgent, OBD-Codes.com warns of transmission damage and stalling, and your brake lights may not work, which puts you at risk from drivers behind you.
Why doesn't my cruise control work with P0703?
RepairPal lists cruise control not working as a P0703 symptom, because the brake switch signal is also used to cancel cruise control.
How much does it cost to fix P0703?
Neither source gives a repair cost. It can be as simple as a fuse or switch adjustment, so get a diagnosis or written estimate before replacing parts.
Sources
Last reviewed 2026-10-25. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.