Theory Of Operation

WARNING: This page is about a different car, the 2016 Jeep Wrangler and 2015 Jeep Wrangler. However, it is still accessible from the selected car via links, so may be relevant.

The Powertrain Control Module (PCM) monitors the vehicle braking using the Stop/Brake Lamp Switch. For accuracy, the PCM monitors two separate brake switch signals. The operating mode of these signals are as follows:

Brake Signal 1 operation: The PCM sends out a 12 volt, low amperage signal, which may not illuminate a test light, on the (B15) Brake Signal 1 circuit. The PCM monitors the voltage on this circuit to indicate if the brake pedal is depressed or released. The Brake Signal 1 signal is normally closed through the Stop/Brake Lamp Switch. When the brake pedal is released, the (B15) Brake Signal 1 circuit is connected to the ground circuit and the PCM reads 0.0 volts on the (B15) Brake Signal 1 circuit. When the pedal is pressed, the path to ground is opened and the PCM reads 12 volts on the (B15) Brake Signal 1 circuit.

Brake Signal 2 operation: 12 volts are sent on the Ignition Switch Start/Run circuit through the Stop/Brake Lamp Switch to the PCM on the (B16) Brake Signal 2 circuit. The PCM monitors the voltage on this circuit to indicate if the brake pedal is depressed or released. No voltage on the (B16) Brake Signal 2 circuit indicates to the PCM that the pedal is pressed, and 12.0 volts indicate that the brake pedal is released.