C0561Vacuum Sensor A/B Correlation
- Generic OBD-II code · Chassis
- Can trigger limp mode
- How the car detects it
- Where two vacuum signals describe the brake booster supply, the module expects them to track each other; C0561 means sensor A and sensor B disagree beyond the allowed band. No maker documents this code number publicly. The principle is patented: Ford compares the booster vacuum sensor with a second reservoir sensor after the vacuum pump stops and flags a sensor mismatch; GM checks the booster sensor against manifold vacuum at closed throttle and marks it biased high or low after set times. Sensors such as HELLA's run on 5 V and output 0.5–4.5 V. GM uses C0561 differently: in its brake modules it means stability control was disabled because another module reported a fault. Brake assist and stop/start may be limited.
- What you may notice
- Brake or stability warning lamp
- Electric vacuum pump runs too often or not at all
- Stop/start or brake assist unavailable on some cars
- Likely causes
- LikelyOne vacuum sensor drifting or reading offset
- PossibleLeaking or kinked vacuum hose or check valve between the two measuring points
- PossibleCorroded connector or damaged wiring on one sensor
- RareUnstable 5 V reference or ground shared by the sensors
- Repair
- Medium · Often possible to do yourself.Typical cost: €20 – €300
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.