Skip the auto shop - Our mechanics make house calls

P0703 OBD-II Trouble Code: Torque Converter/Brake Switch B Circuit Malfunction

check engine light

P0703 code definition

A P0703 code means the PCM has registered a fault in the brake switch B circuit. This is the dedicated stop lamp circuit, which also deactivates the cruise control system and transmission torque converter lockup system, as well as the stop lamps.

What the P0703 code means

With a P0703 code, the PCM has registered a voltage or resistance reading from the brake lamp circuit that’s out of normal spec, triggering a hard code and an illuminated malfunction indicator lamp (MIL). The ABS controller is what passes brake lamp voltage information on, sometimes using the CAN bus system to transfer data between individual modules. When the transmission control system (usually in the PCM) gets an unusual reading on brake lamp voltage and resistance, this code will be stored.

What causes the P0703 code?

Commonly, this code is due to a failed or misadjusted brake lamp switch or blown fuse in the stop lamp circuit. Faulty brake bulb sockets, blown bulbs or shorted, open or corroded wiring/connectors can cause this fault code as well.

What are the symptoms of the P0703 code?

  • Inoperative brake lamps
  • Brake lamps that never shut off and are always illuminated
  • Failure of the torque converter to lock up
  • Stalling while stopped and in gear, due to failure of the torque converter lockup to disengage
  • Stored trouble code
  • Illuminated MIL
  • Other codes related to torque converter, torque converter clutch or torque converter lockup

How does a mechanic diagnose the P0703 code?

For most OBD-II equipped vehicles , the stop lamp switch also deactivates the torque converter clutch and cruise control, as well as engaging brake lamp illumination. Most stop lamp switches are of the on/off variety and are mounted on the brake pedal’s support bracket. Designs can vary greatly – some models have the switch mounted on the pedal lever itself, using the lever’s pivot point as the fulcrum to move contacts, opening and closing the circuit.

In any design, the constant voltage is present on one side of the switch; when the switch’s contacts are closed, voltage moves across the switch’s contacts and on to another application. Your diagnosis will begin with a visual inspection of all wiring and connectors. Repair/replace any damaged, disconnected, shorted or corroded wiring, connectors or components as needed. Retest the system after repairs.

For further diagnosis, you’ll need a manufacturer’s wiring schematic, OBD-II scanner or code reader and a digital volt/ohmmeter. Inspect the PCM’s wiring and connectors and repair any damaged, disconnected, shorted or corroded wiring, connectors or components as needed. Retest the system. If all wiring and components seem to be in good working order, connect the code reader to the diagnostic port and record any stored codes. Clear the codes and test drive the vehicle to see if the code registers again.

If the code doesn’t register again, you may have an intermittent condition which might need to be allowed to worsen before a correct diagnosis and repair can be made. If the code immediately registers again:

  • Check for battery voltage on the stop lamp switch’s input side, using the volt/ohmmeter

  • If no voltage can be found on the input side, disconnect any related control modules and check for continuity between the system fuse and stop lamp switch input circuit. Repair open or shorted circuits as needed.

  • If voltage is present on the stop lamp switch’s output side, check for voltage on the output side with the brake pedal depressed.

  • If you find voltage on the input side but none on the output side (with brake pedal depressed), the problem may be a failed or misadjusted stop lamp switch. Most stop lamp switches are adjustable – adjust or replace the switch and retest the system.

  • If voltage is present on the input and output sides of the stop lamp switch, with the brake pedal depressed, check the brake lamps to see if they are working properly. If not, test the turn signal switch for battery voltage while brake pedal is depressed. Test input and output sides of the turn signal switch. Refer to a factory wiring diagram for proper wiring color and location.

  • If everything else checks – voltage present at output circuit of the stop lamp switch and turn signal switch, and brake lamps are working properly – check circuit continuity and resistance between the stop lamp switch and PCM. Be sure to check all circuits, using vehicle wiring diagram. Repair/replace any open or shorted circuits or connectors.

  • If no other problems are apparent, suspect a defective PCM but remember that a failed PCM is rare and will require reprogramming to replace.

Common mistakes when diagnosing the P0703 code

While a problem with a stop lamp switch is fairly simple, it can be accompanied by other codes that can lead a technician to troubleshoot the torque converter clutch lockup solenoid or wiring.

How serious is the P0703 code?

A P0703 code can lead to brake lamps not working or staying lit all the time, which is very dangerous. It can also lead to the torque converter failing to lock up, or the lockup circuit failing to disengage, which can lead to stalling problems or other drivability issues.

What repairs can fix the P0703 code?

Additional comments for consideration regarding the P0703 code

As with other diagnostics, a P0703 code can only point a technician in the right direction. It’s important to follow a process of elimination in order to reach a correct diagnosis for a P0703 code, before replacing any parts.

Need help with a P0703 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the...
P0222 OBD-II Trouble Code: Throttle/Pedal Position Switch/Sensor B Circuit Low Input
P0222 code definition Throttle/Pedal Position Switch/Sensor B Circuit Low Input What the P0222...
How to Transfer a Car Title in Idaho
In order to prove ownership of a car, you must have the title. However, when a car is sold, given away or inherited, the title needs...


Related questions

Q: Throttle body error codes. Car still accelerates.

The codes should have cleared when the battery was disconnected. I would suggest driving the car as normal for a bit to see if they come back on. Chances are if the car is running normally, they have been cleared...

Q: Code P0340

Hello. Code P0340 sets due to many possible faults. The sensors themselves have to be tested using an oscilloscope to see if the output waveform meets spec. If the sensors were not tested, there may have been nothing wrong with...

Q: Vehicle shuts off intermittently at idle

The P0113 code relates to a problem with the intake air temperature (IAT) sensor. The computer is seeing a reading that is outside of its normal parameters and is causing the computer to set the code. This could also be...