GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC P0719: Brake Switch Circuit Low Voltage

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Brake Position Sensor Signal

C0277 06

C0277 06

C0277 07

C0277 09

Stop Lamp Relay Control

1

1

1

--

Stop Lamp Switch Signal

P0572, P0719

BP0573, P0719

P0573, P0724

--

Stop Lamp Relay Switch B+

1

1

--

--

Brake Position Sensor 5-Volt Reference

C0870 03

C0870 03

C0870 07

--

Brake Position Sensor Low Reference

--

C0277 06

C0277 07

--

Left Rear Stop/Turn Lamp Supply Voltage

1

1

1

--

Right Rear Stop/Turn Lamp Supply Voltage

1

1

1

--

Center High Mounted Stop Lamp (CHMSL) Ground

--

1

1

--

Rear Stop/Turn Lamp Ground

--

1

1

--

1. Stop Lamps Malfunction

Circuit/System Description

The brake pedal position sensor is used to sense the action of the driver application of the brake pedal. The brake pedal position sensor provides an analog voltage signal that will increase as the brake pedal is applied. The body control module (BCM) provides a low reference signal and a 5-volt reference voltage to the brake pedal position sensor. When the variable signal reaches a voltage threshold indicating the brakes have been applied, the BCM will apply battery positive voltage to the stop lamps, transmission control module (TCM), engine control module (ECM), and stop lamp relay coil side. The BCM also supplies the stop lamp relay coil with ground. When the stop lamp relay receives battery voltage and ground from the BCM, the relay coil is energized and the stop lamp relay switch contacts close applying battery voltage through the STOP/B/U/LPS fuse to illuminate the center high mounted stop lamp (CHMSL).

Conditions for Running the DTC

    • DTCs P0722 or P0723 must not be set as current.
    • DTC P0724 must not be set as current.
    • With the brake switch high and vehicle speed less than 8 km/h (5 mph) then vehicle speed is greater than 8 km/h (5 mph), but less than 40 km/h (25 mph) for less than or equal to 6 seconds, then vehicle speed is greater than 40 km/h (25 mph) for 7 seconds.

Conditions for Setting the DTC

The TCM detects an open or short to ground on the signal circuit when the serial data message from the BCM indicates the brakes are applied.

Actions Taken When the DTC Sets

    • The TCM does not request the ECM to illuminate the malfunction indicator lamp (MIL).
    • The TCM records the operating conditions present when the Conditions for Setting the DTC are met. The TCM records this information as a failure record.
    • Stores DTC P0719 in TCM memory.

Conditions for Clearing the DTC

    • The condition responsible for setting the DTC no longer exists.
    • You issue a scan tool CLEAR DTCs command.
    • A history DTC will clear once 40 malfunction-free ignition cycles have occurred.

Diagnostic Aids

Important: The stop lamps will not illuminate unless the ignition is in the ON position. For more detailed information concerning stop lamp operation, refer to Exterior Lighting Systems Description and Operation .

Verify that the brake pedal position sensor is properly calibrated.

Reference Information

Schematic Reference

Exterior Lights Schematics

Connector End View Reference

Lighting Systems Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

    •  Scan Tool Output Controls
    •  Scan Tool Data List
    •  Scan Tool Data Definitions

Circuit/System Testing

  1. Ignition OFF, disconnect the harness connector at the TCM.
  2. Connect a test lamp between stop lamp switch signal circuit and ground.
  3. Ignition ON, command the stop lamp relay control ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
  4. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, replace the TCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Brake Pedal Position Sensor Calibration
    •  Control Module References for BCM and TCM replacement, setup, and programming