Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Component Functional Description - Brake Switch
The Powertrain Control Module (PCM) monitors the vehicle braking using the Brake Switch. For accuracy, the PCM monitors two separate Brake Switch signals. The PCM runs a diagnostic to monitor the operation and rationality of both switch inputs. The switches do not apply simultaneously and are configured differently (see below).
- Brake Switch 1 is in the normally open state at rest (NOT PRESSED).
- Brake Switch 2 is in the normally closed state at rest (NOT PRESSED).
Brake Signal 1 Operation: Battery voltage is provided to the Brake Switch 1 portion of the Brake Switch. The voltage passes through the normally open switch to the PCM on the Brake Signal 1 circuit when the Brake Switch is PRESSED. Brake Switch 1 closes at initial pedal application and is solely responsible for disabling cruise control. Since Brake Switch 1 is solely responsible for disabling cruise control, it is also checked for a stuck on and stuck off condition. The Brake Signal 1 circuit is hard-wired to the PCM. On some vehicles it is also hard-wired to the BCM and security module.
Brake Signal 2 Operation: Battery voltage is provided to Brake Switch 2 of the Brake Switch. When the Brake Pedal is NOT PRESSED, voltage passes through the normally closed switch to the Brake Signal 2 circuit. The Brake Signal 2 circuit is hard-wired to the BCM and is transmitted to the PCM over CAN C bus. On a properly functioning switch, Brake Switch 1 will always change states before Brake Switch 2. This is important to understand for the Brake Switch rationality diagnostic.
The voltage readings on each signal circuit on a normally functioning switch should match the table below. The PCM monitors the voltage on each circuit to determine the Brake Pedal position and for rationality checks. TECH TIP: On this switch the PCM should never see 12.0 volts or 0 volts simultaneously on both signals with the Brake Pedal fully Pressed and Released if there are not faults in the switch or wiring.
| BRAKE SWITCH SIGNAL | PHYSICAL BRAKE PEDAL STATE | SIGNAL CIRCUIT VOLTAGE |
|---|---|---|
| BRAKE SIGNAL 1 (NORMALLY OPEN) | NOT PRESSED | 0 volts |
| PRESSED | 12 volts | |
| BRAKE SIGNAL 2 (NORMALLY CLOSED) | NOT PRESSED | 12 volts |
| PRESSED | 0 volts |
- The Brake Switch 1 rationality diagnostic will fail immediately if the PCM receives a Brake Switch 2 PRESSED signal with Brake Switch 1 NOT PRESSED signal. In some cases Brake Switch 1 can be applied without Brake Switch 2 due to an improperly adjusted switch or during two foot driving conditions. It is important to confirm that these conditions do not exist.
- Brake Switch 2 rationality diagnostic will fail after the PCM sees approximately 50 consecutive state changes of Brake Switch 1 with no changes in Brake Switch 2.
- The Brake Switch stuck on test will set a fault if the Brake Switch is determined to be applied (brake pedal Pressed for both switches) when the vehicle is moving. Once the diagnostic is enabled, if the Brake Switch is seen as applied (PRESSED for both signals), a fail timer will start to count in one second increments. This timer can be decremented if the Brake Switch state returns to the off (NOT PRESSED for both signals) position. If the fail timer reaches a calibrated fail time, a malfunction will be declared and the timer will be reset.
- The Brake Switch stuck off test looks for no sign of the Brake Switch applied (brake pedal PRESSED) during repeated stopping maneuvers. If the vehicle comes to a complete stop and the Brake Switch state is off (NOT PRESSED for both signals), a fail timer will start to count in one second increments. If the Brake Switch state changes to applied (PRESSED for both signals), the fail timer will decrement back down to zero. If the fail timer reaches a calibrated fail time, a malfunction will be declared and the timer will be reset.
Since Adaptive Cruise Control (ACC) is capable of bringing the vehicle to a complete stop, this diagnostic could potentially false fail because the vehicle reaches a vehicle speed of zero without the brake pedal being pressed. If ACC system is actively applying the brakes this diagnostic will be disabled to avoid a false failure.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.