OBD-II code C0548 indicates that the control module has detected a low voltage condition in the supply circuit for a vacuum sensor. This sensor is often used to monitor brake booster vacuum or HVAC system vacuum, and the low voltage may be caused by a short to ground, a faulty sensor, or wiring issues.
The vacuum sensor itself may have an internal short or failure, causing it to draw excessive current and pull the supply voltage low.
Wiring between the control module and the sensor may be chafed, pinched, or damaged, creating a direct path to ground and reducing voltage.
Corrosion, loose terminals, or backed-out pins in the sensor connector can cause high resistance and a voltage drop in the supply line.
A poor ground connection for the sensor can cause the supply voltage to read low, as the reference voltage is measured relative to ground.
In rare cases, the control module's internal voltage regulator or driver circuit may fail, but this should only be considered after all other causes are ruled out.
It means the control module has detected that the voltage supplied to a vacuum sensor is below the expected range, which can affect systems like brake boost or HVAC controls.
It depends on the affected system. If the brake booster vacuum sensor is involved, you may experience a hard brake pedal and increased stopping distance, making driving unsafe. If it's an HVAC sensor, the vehicle may be drivable but climate control functions could be impaired.
No, the engine or chassis control module is rarely the cause. The problem is almost always a faulty vacuum sensor, damaged wiring, or a poor connection. Replacing the module without proper diagnosis is often a misdiagnosis.
Start by inspecting the sensor and its wiring. If the sensor is shorted internally, replace it. Repair any damaged wiring or corroded connectors. Only after confirming all external components are good should the control module be suspected.