C0550 code meaning
Vacuum Sensor B Circuit High
What C0550 means
Vacuum sensor B puts out more voltage than its design permits. HELLA caps the output of its booster sensor at 4.8 V, with 4.5 V already standing for −1000 hPa, so anything above is a wiring or sensor fault: signal touching the supply or battery voltage, a broken ground return or a failed sensor. Because a high voltage simulates strong vacuum, the control unit must not rely on it for switching the electric vacuum pump; Bosch describes that pump control as the core job of the measurement. Mitsubishi's brake unit catches vacuum sensor shorts within a second and suspends brake assist. No maker documents C0550 with this meaning; one GM bulletin cites C0550 at a rear differential clutch module, a GM-specific use. C054F is the low counterpart, C054C the same fault on A.
C0550 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyEasy, DIY possible
- Typical labor0.2 to 1.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of C0550
- Brake assist or brake system warning on
- Firm pedal possible if the pump is not switched on when needed
Common causes of C0550
- Most likelySignal of sensor B shorted to supply or battery voltage
- PossibleGround return of sensor B broken
- Less likelySensor B stuck at high output
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Vacuum sensor bSensor wiring
What each part of C0550 means
| C | Chassis system: brakes, ABS, steering and suspension. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 50 | The exact fault in that area. |
What to do next
- Note C0550 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 C0550
What does C0550 mean?
C0550 means "Vacuum Sensor B Circuit High". Vacuum sensor B puts out more voltage than its design permits. It is a generic code, so it means the same on every make.
Is it safe to drive with C0550?
Drive gently and only to a workshop. With C0550 the car can go into limp mode (reduced power) to protect itself.
Will C0550 fail an emissions test?
C0550 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 C0550 to fix?
Difficulty: easy. A typical repair takes 0.2 to 1.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will C0550 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.