C0548 code meaning
Vacuum Sensor Supply Voltage Low
What C0548 means
The supply reaching the vacuum sensor is present but sags below its lower limit. With a ratiometric sensor every output voltage scales with the feed, so an under-supplied sensor reports a wrong vacuum even if it is healthy. HELLA rates its brake booster vacuum sensor for 4.5 to 5.5 V and maps 0 to −1000 hPa onto 0.5 to 4.5 V; a feed near the bottom of that window already shifts the reading. On a Saab 9-5 the brake module reacts to a sensor supply under 4.4 V within 0.06 s. Typical causes are a weak module output, an extra load on a shared 5-V rail or high resistance in the feed wire. No maker documents C0548 publicly. C0547 covers an open or shorted supply, C054B and C054F low sensor signals.
C0548 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyMedium, DIY possible
- Typical labor0.3 to 2 hours
- Clears after repairWhen cleared with a scanner
Symptoms of C0548
- Brake or ESC warning lamp on
- Vacuum reading implausible in live data
- Further codes for sensors on the same supply
Common causes of C0548
- Most likelyAnother sensor on the same 5-V rail drawing it down
- PossibleCorroded contact or damaged feed wire adding resistance
- Less likelyWeak sensor supply output in the control module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Vacuum sensorSensor supply
What each part of C0548 means
| C | Chassis system: brakes, ABS, steering and suspension. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 48 | The exact fault in that area. |
What to do next
- Note C0548 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about C0548
What does C0548 mean?
C0548 means "Vacuum Sensor Supply Voltage Low". The supply reaching the vacuum sensor is present but sags below its lower limit. It is a generic code, so it means the same on every make.
Is it safe to drive with C0548?
Drive gently and only to a workshop. With C0548 the car can go into limp mode (reduced power) to protect itself.
Will C0548 fail an emissions test?
C0548 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is C0548 to fix?
Difficulty: medium. A typical repair takes 0.3 to 2 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will C0548 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.