C0548Vacuum Sensor Supply Voltage Low
- Generic OBD-II code · Chassis
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- Brake or ESC warning lamp on
- Vacuum reading implausible in live data
- Further codes for sensors on the same supply
- Likely causes
- LikelyAnother sensor on the same 5-V rail drawing it down
- PossibleCorroded contact or damaged feed wire adding resistance
- RareWeak sensor supply output in the control module
- Repair
- Medium · Often possible to do yourself.Typical cost: €30 – €300
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.