P0719 indicates the powertrain control module has detected a low voltage condition on the brake switch B input circuit when it expects a high signal. Brake switch B is typically the normally-closed side of the brake pedal switch, used by the PCM for torque converter clutch and cruise control decisions rather than for the brake lamps themselves.
The internal contacts of the brake switch can wear, stick, or corrode, causing the B circuit to report low voltage continuously. This is the most common cause of P0719.
Chafed, shorted, or corroded wiring, or a damaged connector at the brake switch, can pull the B circuit low or interrupt the expected signal.
If the switch is mounted out of position or the pedal stop is worn, the switch may not open and close at the correct pedal travel, causing an incorrect state at the PCM.
A fuse feeding the reference or signal side of the brake switch B circuit can be open, resulting in a permanent low voltage reading at the PCM.
Rarely, the PCM input circuitry for the brake switch B signal may fail. This should only be considered after the switch, wiring, and power supply are fully verified.
Short distances are usually possible, but cruise control and torque converter clutch control may be disabled, and some vehicles may not start. Have it diagnosed promptly.
In most jurisdictions, a stored code with the check engine light on will cause an OBD-II emissions test failure regardless of whether the fault is emissions-related.
Almost never. The brake switch and its wiring are by far the most likely causes. PCM replacement should only be considered after the switch, fuse, and harness have been definitively verified as good with proper electrical testing.
Yes. The PCM uses the brake switch B input to manage torque converter clutch release and, on some vehicles, shift logic. A faulty signal can cause abnormal lockup or shift behavior.