OBD-II trouble code
U043F: Invalid Data Received From Vacuum Sensor B
A module is receiving messages from vacuum sensor 'B', but the pressure/vacuum data inside them is implausible or out of range. The 'B' counterpart to U043E — same fault pattern, a second sensor location or system.
Quick facts
- System
- Network
- Category
- Network Communication
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $100 – $700
- DIY difficulty
- Shop recommended
What does U043F mean?
U043F is the 'B' counterpart of U043E. On vehicles that use more than one vacuum sensor, sensor 'B' watches a second location or system — for example, the opposite side of a dual brake-boost or emissions arrangement, a separate vacuum reservoir, or a different point in the intake/boost path. Like sensor 'A', it broadcasts its pressure reading onto the vehicle network so a receiving controller can act on it. U043F sets when that controller is still hearing from vacuum sensor 'B', but the value in its messages is invalid: out of range, implausible, or contradicting what related sensors report. The link is alive; the content can't be trusted — the classic distinction from a lost-communication code, which means the sensor has gone completely silent.
Because the fault is bad data rather than a dead bus, the causes are the same family that affects sensor 'A': a failing or drifting sensor element, a cracked or disconnected vacuum hose that starves the sensor of a realistic signal, moisture or corrosion at the connector, chafed signal wiring, low system voltage, or software that is outdated or was never re-flashed after a replacement. When U043E and U043F appear together, suspect something common to both — a shared power/ground feed, a shared bus segment, or a module-side software problem — rather than two sensors failing independently at once.
Symptoms track whatever sensor 'B' governs on the specific vehicle: a firmer brake pedal or brake-assist warning if it monitors booster vacuum, an emissions fault or failed readiness monitor if it feeds EVAP/emissions logic, or minor driveability changes if it watches intake or boost vacuum. Often the check engine light is the only visible sign, because the receiving module simply defaults around the bad reading. The car usually stays driveable, but because U043F is often a secondary code, read the full list first — a companion pressure, EVAP, or vacuum code frequently names the real root cause, and a cracked hose or corroded connector is a common, inexpensive fix.
Common causes
- Failing or drifting vacuum sensor 'B' element reporting an implausible value
- Cracked, collapsed, or disconnected vacuum hose starving the sensor of a real signal
- Moisture, corrosion, or a loose pin at the sensor connector
- Chafed or shorted signal wiring corrupting the value in transit
- Low system voltage or a poor ground destabilizing the reading
- Shared power/ground or bus-segment fault (especially if U043E is also present)
- Outdated or mismatched software after a sensor or module replacement
- Internal sensor fault
Symptoms
- Check engine light, sometimes the only visible symptom
- Firmer brake pedal or a brake-assist warning if sensor 'B' monitors booster vacuum
- Emissions-related fault or failed readiness monitor if it feeds EVAP/emissions logic
- Minor driveability changes if it watches intake or boost vacuum
- Companion pressure, EVAP, or vacuum codes — often U043E — stored alongside U043F
Diagnostic steps
- 1.Read ALL stored codes first — U043F is often secondary to a pressure, EVAP, or vacuum code that names the real fault.
- 2.Note whether U043E is also present; if both are set, look for a shared power, ground, or bus cause rather than two failed sensors.
- 3.Identify what vacuum sensor 'B' monitors on this specific vehicle before testing.
- 4.Inspect the associated vacuum hoses and lines for cracks, collapse, disconnection, or blockage.
- 5.Check the sensor connector and wiring for corrosion, moisture, looseness, and chafing.
- 6.Compare the sensor's live reading against a known reference (a hand-held vacuum gauge or the expected value at idle/key-on).
- 7.Verify the module has the correct, current calibration, then address companion codes before condemning the sensor.
Repair cost
$100 – $700
Cost mirrors U043E. A cracked or disconnected vacuum hose is a cheap fix at $20-$150. A vacuum/pressure sensor is typically $80-$300 installed. Correcting low voltage or a bad ground runs $150-$400, and repairing a corroded connector varies with access. A module reflash is $100-$200. If both U043E and U043F are present, a single shared cause may fix both — diagnose before replacing either sensor.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with module communication / can bus diagnosis preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
Leave this one to a qualified shop. It typically involves emissions-critical components, refrigerant handling, or other work that requires manufacturer-grade tooling, training, or certification. DIY attempts often produce a more expensive problem than the original code.