C0561

Code

Generic C — Chassis

Vacuum Sensor A/B Correlation

Brand: Generic

Type: C — Chassis

Views: UK: 36 EN: 95 RU: 36

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Faulty vacuum sensor A or B
Damaged or corroded wiring or connectors to one or both sensors
Vacuum hose leak or blockage between sensors and source
Incorrect sensor installation or wrong replacement part
Intermittent connection (loose pin, damaged terminal)
ECU or sensor reference voltage/ground fault

Symptoms

Malfunction Indicator Lamp (MIL) or ABS/traction warning (if integrated)
Poor idle quality or rough running at low engine speeds
Reduced brake assist (on systems using vacuum for booster) or perceived weak braking assist
Loss of engine power or entry into limp/limitation mode on some systems
Reduced fuel economy
Intermittent faults that clear after driving or reconnecting connectors

What to check

Read freeze-frame and live data from the scan tool for both vacuum sensors (A and B)
Compare Sensor A and B voltage/pressure values at key conditions: ignition on, idle, under light and heavy load
Visually inspect sensor connectors, pins, and harness for damage, corrosion, or water ingress
Check vacuum hoses and fittings for leaks, collapsed lines, or blockages; pressure-test or smoke-test the vacuum system
Backprobe sensor signals with a multimeter or oscilloscope to verify voltage range and stability
Verify sensor reference voltage (usually 5 V) and ground integrity at both sensor pins

Signal parameters

Typical sensor output: 0.5–4.5 V (varies by manufacturer); both sensors should track closely across operating range
Correlation threshold: sensors should agree within a small delta (commonly 0.1–0.5 V or within ~10–20% of each other depending on calibrations)
Idle vacuum range: approximate manifold vacuum ~15–22 inHg (varies by engine); both sensors should report similar relative values
Reference supply: stable 5 V reference to sensors and good ground expected

Diagnostic algorithm

Retrieve trouble code, freeze-frame data and note operating conditions when DTC set.
Visually inspect connectors and harness to both vacuum sensors for damage, corrosion, or looseness. Repair as needed.
With a scan tool, monitor Sensor A and B outputs simultaneously at key conditions (key on engine off, idle, light throttle, heavy throttle). Note discrepancies.
Verify sensor reference voltage and ground at each sensor with meter; repair wiring faults.
Pressure/vacuum test the vacuum lines and intake for leaks (smoke test or hand-held vacuum pump). Repair any leaks.
If wiring and vacuum system are good, bench-test or backprobe each sensor to confirm correct voltage response to applied vacuum; replace sensor that fails specification.
If sensors test good and wiring is intact, consider ECU input/ground faults; perform voltage drop tests on ground/reference circuits and review ECU grounds.
Clear codes and perform a road test under conditions that previously set the code to confirm repair. If code returns, capture new data and escalate to ECU/software diagnostics or manufacturer-specific procedures.

Likely causes

Connector damage or corrosion causing one sensor to read low/high
Vacuum line leak upstream of one sensor causing inconsistent pressures
Failed vacuum sensor producing an out-of-range voltage
Short to voltage or ground in sensor harness
Faulty ECU input or poor ground causing incorrect comparison

Fault status

⚠️ Status

Vacuum Sensor A/B Correlation — the control module detected that the outputs of Vacuum Sensor A and Vacuum Sensor B do not agree within expected limits.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours