Failed vacuum sensor A (internal short or open circuit); Damaged or disconnected vacuum hose or tube leading to the sensor; Corroded, loose, or damaged electrical connector at the sensor; Open or shorted wire in the sensor signal circuit (low voltage side); Poor ground connection for the sensor or PCM; Vacuum leak in the intake manifold or brake booster system; Faulty PCM or BCM (rare)

DTC codes / C05xx · Brakes, steering and suspension / C054B

C054BVacuum Sensor A Circuit Low

Q: What does code C054B mean?

Vacuum Sensor A Circuit Low. C054B indicates that the powertrain control module (PCM) or body control module (BCM) has detected a voltage signal from Vacuum Sensor A that is lower than the expected range for the current operating conditions. This sensor monitors vacuum pressure in systems such as the brake booster or EVAP system, and a low signal typically points to a circuit fault, a failed sensor, or a vacuum leak.

C054B indicates that the powertrain control module (PCM) or body control module (BCM) has detected a voltage signal from Vacuum Sensor A that is lower than the expected range for the current operating conditions. This sensor monitors vacuum pressure in systems such as the brake booster or EVAP system, and a low signal typically points to a circuit fault, a failed sensor, or a vacuum leak.

SystemChassis

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaBrakes, steering and suspension

Symptoms you may notice

Illumination of the check engine light or service vehicle soon message
Often no symptoms besides the warning light
Reduced engine performance or poor fuel economy if the sensor affects fuel trim
Hard brake pedal or increased stopping effort if the sensor is part of the brake booster vacuum circuit
Rough idle or stalling due to incorrect vacuum readings affecting air-fuel mixture
Inability to complete an emissions self-test or readiness monitor

Common causes, most likely first

Failed vacuum sensor A (internal short or open circuit)
Damaged or disconnected vacuum hose or tube leading to the sensor
Corroded, loose, or damaged electrical connector at the sensor
Open or shorted wire in the sensor signal circuit (low voltage side)
Poor ground connection for the sensor or PCM
Vacuum leak in the intake manifold or brake booster system
Faulty PCM or BCM (rare)

How to diagnose and fix it

Inspect the vacuum sensor and its connector for physical damage, corrosion, or loose pins
Check all vacuum hoses and tubes for cracks, disconnections, or leaks
Measure reference voltage and ground at the sensor connector with a multimeter
Test the sensor signal voltage with a vacuum pump applied and compare to specifications
Check continuity and resistance of the signal circuit between sensor and PCM
Replace the vacuum sensor if it fails electrical or vacuum testing
Clear the code and verify repair with a test drive and monitor readiness

Don't overlook the simple vacuum leak

A low voltage signal from the vacuum sensor often results from a simple vacuum leak rather than a failed sensor, so always perform a smoke test before replacing parts.
The code can be set by a poor ground connection at the sensor or PCM, which is frequently missed during diagnosis.
On some vehicles, a faulty brake booster check valve or leaking booster diaphragm can cause this code without any obvious brake performance change.
The sensor may share a reference voltage circuit with other sensors, so a short in a related circuit can trigger C054B along with other codes.
Replacing the sensor without checking the wiring harness for chafing or corrosion often leads to a repeat failure.

Can I keep driving with C054B?

If the only symptom is the warning light, the vehicle is generally safe to drive, but avoid heavy braking or towing until the fault is repaired. If you notice a hard brake pedal or reduced engine performance, have the vehicle inspected promptly.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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