Faulty brake booster boost sensor, such as an internal short or open circuit in the sensing element; Damaged or disconnected electrical connector at the boost sensor, including corroded or bent pins; Wiring harness damage between the boost sensor and the control module, such as chafing, open circuit, or short to ground; Failed brake booster check valve or vacuum leak causing the sensor to read an implausible pressure; Malfunctioning brake booster itself, such as a torn diaphragm or internal leak that affects sensor readings; Low brake fluid level or contaminated brake fluid affecting hydraulic pressure sensor readings; Faulty control module, though this is rare and should only be considered after all other causes are ruled out

DTC codes / C02xx · Brakes, steering and suspension / C0279

C0279Brake Booster Boost Sensor Circuit Malfunction

Q: What does code C0279 mean?

Brake Booster Boost Sensor Circuit Malfunction. C0279 indicates that the brake booster boost sensor circuit has a malfunction, meaning the computer has detected an abnormal voltage or signal from the sensor that monitors vacuum or hydraulic pressure assist in the brake booster. The powertrain control module (PCM) or body control module (BCM) sets this code when the sensor's output falls outside the expected range for the current operating conditions, which can affect brake assist and pedal feel.

C0279 indicates that the brake booster boost sensor circuit has a malfunction, meaning the computer has detected an abnormal voltage or signal from the sensor that monitors vacuum or hydraulic pressure assist in the brake booster. The powertrain control module (PCM) or body control module (BCM) sets this code when the sensor's output falls outside the expected range for the current operating conditions, which can affect brake assist and pedal feel.

SystemChassis

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaBrakes, steering and suspension

Symptoms you may notice

Illumination of the anti-lock brake system (ABS) warning light or brake system warning light on the dashboard
A hard brake pedal that requires increased effort to stop the vehicle
Reduced or inconsistent brake assist, especially during low-speed maneuvers or emergency stops
A soft or spongy brake pedal that may sink toward the floor when held
Often no symptoms besides the warning light, with normal brake performance in many cases
Possible activation of the traction control or stability control warning light as a related system

Common causes, most likely first

Faulty brake booster boost sensor, such as an internal short or open circuit in the sensing element
Damaged or disconnected electrical connector at the boost sensor, including corroded or bent pins
Wiring harness damage between the boost sensor and the control module, such as chafing, open circuit, or short to ground
Failed brake booster check valve or vacuum leak causing the sensor to read an implausible pressure
Malfunctioning brake booster itself, such as a torn diaphragm or internal leak that affects sensor readings
Low brake fluid level or contaminated brake fluid affecting hydraulic pressure sensor readings
Faulty control module, though this is rare and should only be considered after all other causes are ruled out

How to diagnose and fix it

Connect a scan tool and record all stored codes and freeze-frame data to confirm C0279 is current and not history
Visually inspect the boost sensor, its connector, and the wiring harness for damage, corrosion, or loose connections
Test the sensor's reference voltage, signal voltage, and ground circuits with a digital multimeter (DMM) to verify proper operation
Check the brake booster vacuum supply and check valve for leaks or blockage using a vacuum gauge
Compare sensor live data against a known-good specification or perform a wiggle test on the harness while monitoring the signal
Replace the brake booster boost sensor if testing confirms it is faulty, then clear codes and verify the repair
If the code persists, diagnose the control module and its programming, and repair or replace as needed

What the boost sensor code really means

A boost sensor code often sets because of a simple vacuum leak at the booster check valve or a cracked vacuum hose, not because the sensor itself has failed.
Many vehicles will set C0279 intermittently due to a poor electrical connection at the sensor, so a thorough wiggle test of the connector and harness is essential before replacing parts.
The boost sensor may share its reference voltage or ground circuit with other sensors, so a fault in a shared circuit can trigger multiple codes and mislead diagnosis.
A hard brake pedal with this code does not always mean the booster has failed; the sensor may be reporting incorrectly while the booster still provides adequate assist.
After replacing the sensor, some vehicles require a calibration or relearn procedure for the brake system, which a scan tool must perform to prevent the code from returning.

Can I keep driving with C0279?

If the brake pedal feels normal and the warning light is the only symptom, you can drive cautiously to a repair shop, but avoid heavy braking or towing. If the pedal is hard or braking performance is reduced, stop driving and have the vehicle towed, as brake assist may be compromised.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.