A 2022 Chevrolet Equinox rolled in for an inspection, and a routine scan pulled a lone P0703 code with no obvious drivability complaints attached. The technician's notes simply stated they found the diagnostic trouble code while inspecting the vehicle. I see this pattern frequently in the diagnostic platform we build, where a control module flags a fault before the driver ever notices a symptom.
The Dual Nature of the Brake Switch
The most likely culprit, ranked at 75 percent probability in our data, is a faulty Brake Pedal Position (BPP) sensor. The complexity here lies in the sensor's internal design. Modern brake switches use multiple internal electrical circuits. While the "A" circuit typically controls the brake lights, the dedicated "B" circuit is reserved for powertrain control.
An internal malfunction, contact wear, or a broken plastic plunger can prevent this "B" circuit from sending an accurate signal to the Engine Control Module (ECM) and Brake System Control Module (BSCM). This is why a vehicle can have functioning brake lights but still throw a P0703. The ECM requires this specific signal for cruise control deactivation, torque converter clutch operation, and shift interlock logic. The recommended approach is to verify the BPP sensor status using scan tool live data, followed by a direct continuity test of the sensor itself.
Vulnerabilities Under the Dashboard
If the sensor tests fine, the next target is the wiring harness and connectors leading to it, which our data ranks at a 65 percent probability. The BPP sensor lives under the dashboard. This location makes it highly susceptible to physical damage from foot traffic, abrasion, and moisture ingress from wet boots.
In GM vehicles like this Equinox, communication often relies on the Body Control Module and the GMLAN network. An open circuit, a short to ground, or excessive resistance in the "B" circuit wiring will stop the signal dead in its tracks. A thorough visual inspection of the connector for corrosion or poor terminal tension is required, along with voltage, ground, and continuity tests of the wiring harness.
Mechanical Alignment and Power Supply
Sometimes the electrical components are perfectly fine, but the physical alignment is off. Ranked at 55 percent is a misadjusted BPP sensor. If the sensor is improperly seated on its mounting bracket, or if the rubber stopper pad on the brake pedal arm is worn or missing, the plunger cannot fully extend or retract. The control modules then receive a signal that makes no sense for the pedal's physical position. Fixing this requires a visual check of the pedal stop and live data monitoring during pedal actuation.
Finally, a blown "STOP" or "BRAKE LAMP" fuse sits at a 45 percent probability. The "B" circuit needs its own power to operate, and a blown fuse interrupts that supply. Even if a fuse looks intact to the naked eye, it can fail under load, making a continuity test essential.
Looking Forward
Finding a fault code before a customer complains about drivability gives a workshop the upper hand. Do you often see these secondary brake circuits triggering codes before the driver notices a problem in your own bays?
Reference pages for the codes in this article
- P0703, what we measure for this code across real diagnostics