P0703: How to Diagnose & Fix — Brake Switch B Circuit Malfunction
2 vehicles · 2 makes · $30-$4,000 repair
How to diagnose and fix P0703: most-reported vehicles
Ranked by owner reports. Each card gives the symptoms, how to confirm the cause, the fix, parts and sources for that vehicle.
Chevrolet Malibu · 2004–2012
A recurring issue on 2004-2012 Malibu models (including the 2004-2007 Malibu Maxx) is increased resistance at the Body Control Module (BCM) connection, which causes voltage fluctuations in the Brake Apply Sensor (BAS) circuit, leading to inoperative brake lights, cruise control cancellation problems, or the shifter moving out of Park without the brake applied. Some owners also report intermittent brake lamps staying on or not illuminating consistently. Because the stoplamp signal is shared with several systems, a single sensor-circuit fault can create multiple confusing symptoms at once.
Common Symptoms
- Brake lights inoperative
- Shifter moves out of Park without pressing the brake
- Cruise control not working or hard to disengage
- Brake lights stay on
- Intermittent stoplamp operation
- Shift interlock malfunction
How to Fix
This condition is covered by NHTSA safety recall 14V252 (GM 13036): dealers attach the wiring harness to the BCM with a spacer, apply dielectric lubricant to the BCM and BAS connectors, and relearn the brake pedal home position free of charge — check the VIN for open recalls first. Diagnosis should verify brake lamp operation and voltage in and out of the brake apply sensor. Also inspect the fuse, lamp sockets, and shift interlock operation to rule out secondary wiring issues.
Sources for this issue (1)
Ford Bronco · 1990–1996
The electronically controlled E4OD 4-speed automatic behind the V8s is notorious for failing, especially with age, towing, off-road use, or an undersized/overheated cooler. It is heat-sensitive, and a well-documented secondary killer is the brake-light circuit: the PCM watches brake-light voltage to unlock the torque converter, so a shorted/failed brake light, brake-switch wiring, four-way flasher activity, or non-resistive LED bulb swap can make the converter cycle improperly and burn up the transmission. Owners also report the O/D-off light flashing (stored fault), harsh or missing shifts, and failure to shift out of high range from a lost power feed.
Common Symptoms
- Slipping or harsh/erratic shifts
- Overdrive-off (O/D) light flashing
- Won't shift out of high range / stuck in gear
- Torque converter cycling; overheating and burnt fluid smell
- Repeat transmission failures traced to brake-light wiring short
How to Fix
Repair the root cause first: fix any brake-light short/failure, verify the transmission power feed and clean grounds, and avoid non-resistive LED brake bulbs. Address slipping/burnt units with a rebuild (often upgraded with a larger auxiliary cooler and improved valve body/servo). Keep the fluid cool and serviced; add a proper external cooler if towing or wheeling.
Sources for this issue (1)
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P0703 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0703 mean?
P0703 stands for "Brake Switch B Circuit Malfunction." This code means the engine/transmission computer detected an out-of-range or implausible signal from the brake switch (circuit B). The brake switch tells the PCM/TCM when the brakes are applied, which affects cruise control, torque converter lockup, and certain shift and idle strategies. A faulty signal can cause issues like cruise control not working, harsh shifts, or the converter not unlocking.
What are the most common causes of P0703?
The most common causes of P0703 are: Faulty brake light switch, Misadjusted brake switch, Open or shorted brake switch wiring, Corroded or loose connector at the switch, Blown brake circuit fuse, PCM/TCM input fault. The specific cause varies by vehicle.
How much does it cost to fix P0703?
Repair costs for P0703 range from $30 to $4,000, depending on the vehicle and root cause.
Which vehicles are affected by P0703?
Au7o has documented P0703 across 2 vehicle models from 2 manufacturers: Chevrolet, Ford.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.