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Summary
  • Diagnostic trouble code (DTC) P0703 stands for “Brake Switch ‘B’ Circuit.” This means the powertrain control module (PCM) detects a signal from the brake switch that doesn’t meet the expected values.
  • Common causes of the P0703 code include brake switch failure, wiring issues, and damaged connectors in the brake switch’s “B” circuit.
  • Some common symptoms associated with the P0703 code include an illuminated malfunction indicator lamp (MIL) or check engine light, non-functioning brake lights, and non-functioning cruise control.

Finding out what a trouble code means is the first step in fixing it. If this is your first time dealing with the P0703 code, this guide will help you understand its definition, possible causes, and symptoms.

What Does the P0703 Code Mean?

Diagnostic trouble code (DTC) P0703 stands for “Brake Switch “B” Circuit.” This code can be set when the powertrain control module (PCM) detects a signal from the brake switch that doesn’t meet the expected values.

The brake switch is responsible for telling the PCM that the brake pedal is engaged. It also controls the brake lights. If the PCM receives signals from this  part that do not match the predetermined values, it can set the P0703 code.

See also  P0504 Code: Brake Switch A/B Correlation Code
brake light switch
The P0703 code can be set when the PCM detects a signal from the brake switch that doesn’t meet the expected values.

Note: The definition of code P0703 may be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

What are the Common Causes of the P0703 Code?

There are a few things that can cause the P0703 code to set. Here are some of the most common problems that can trigger this code:

  • Brake switch failure
  • Wiring issues, such as shorted or open wiring in the brake switch’s “B” circuit
  • Damaged connectors in the brake switch’s “B” circuit
  • Blown fuse or fusible link
  • PCM failure
car fuse
A blown fuse may trigger the P0703 code.

What are the Common Symptoms of the P0703 Code?

If you’re dealing with the P0703 code, you may notice a few unusual things going on with your vehicle, such as the following:

  • Illuminated malfunction indicator lamp (MIL) or check engine light
  • Brake lights aren’t functioning
  • Cruise control isn’t functioning
  • Engine is stalling when the vehicle rolls to a stop
  • TCC lockup may be disabled
  • Decreased fuel efficiency
  • Diminished engine performance, especially at highway speeds
  • Malfunctioning transmission shift patterns
  • Gear selector won’t come out of “park”

How to Diagnose the P0703 Code

If you have experience using a scan tool, you can monitor the brake light switch input using a scan tool while operating the brake as an initial test.

On most vehicles, the brake switch doesn’t actively close the circuit to carry current. Rather, it sends a signal to one or more modules. The module(s) receiving the signal will store the brake pedal position (BPP) switch code, usually when there are tandem switches as in the diagram, and one switch closes but the other switch doesn’t.

See also  P0572 Code: Brake Switch “A” Circuit Low
brake pedal position switch diagram showing tandem switches
Brake pedal position switch diagram showing tandem switches | Source: Richard McCuistian

The ECM/PCM and/or the BCM will receive the BPP switch input for various reasons on modern vehicles.

As an example, GM (2006 Chevrolet Impala) describes BPP switch operation this way: “The body control module (BCM) monitors the brake pedal position sensor. When the brake pedal is applied, the BCM detects a predetermined voltage signal. The BCM sends a GMLAN serial data message to the engine control module (ECM) indicating the status of the stop lamps.”

Keep in mind however, that there are several possible causes of DTC P0703. If you encounter this code, you might need to consult a certified mechanic or technician to get to the bottom of things.

However, if you want to do a bit of research on your own so that you can understand the P0703 code, there are a few resources that can explain the diagnostic and repair procedures for this trouble code in more detail.

The following video contains information that you might find helpful in figuring out what the diagnostic process might involve:

How to Fix the P0703 Code

Several trouble codes can share the same affected areas, symptoms, and even possible causes, but that doesn’t mean that there’s a single cure-all solution for all of them. Determining the exact cause is your best bet in fixing any trouble code, including the P0703. Plus, different vehicle makes have different diagnostic and repair procedures. That means you also have to determine the prescribed procedures for your specific vehicle.

See also  P0571 Code: Cruise Control / Brake Switch A Circuit Malfunction

Good thing there are a few auto repair resources and guides you can use to learn more about trouble codes and how to fix them. Repair manuals, in particular, are one of the most reliable sources you can count on for OBD-II diagnosis and repairs. They contain detailed, vehicle-specific, step-by-step guides, illustrations, and diagrams.

If you’re not confident in your OBD-II repair know-how, it’s best to have a certified mechanic or technician do the job for you, so that you can avoid expensive mistakes down the line.

Other Notes About P0703

The P0703 code should be addressed as soon as possible. If left unfixed, your transmission might be severely damaged. In many vehicle models, the PCM will be able to disable the torque converter clutch lockup and place the transmission control system in limp-in mode. The trouble code P0703 only sets in vehicles with automatic transmissions.

Driving with this code isn’t advised, as it can cause multiple issues. If you encounter this code, it’s best to bring your vehicle to a shop for repairs as soon as possible.

About The Authors
Written By Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at CarParts.com

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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