P0240

Code

Generic P — Powertrain

Turbocharger/Supercharger Boost Sensor B Circuit Range/Performance

Brand: Generic

Type: P — Powertrain

Views: UK: 27 EN: 45 RU: 41

AI status

Completed

ready

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Page language: EN

Causes

Open or short in Boost Sensor B signal, reference, or ground circuit
Faulty turbo/supercharger boost (MAP) sensor B
Corroded or loose connector pins
Vacuum or boost hose leak between turbo and sensor
Intermittent wiring damage from heat, chafing or rodent damage
Faulty ECM (rare)

Symptoms

Check Engine Light (MIL) illuminated
Reduced engine power or limp-home mode
Poor acceleration or hesitation under boost
Incorrect or erratic boost gauge/reading
Increased fuel consumption or rough running under load
Possible turbo wastegate control issues (overboost or underboost)

What to check

Read and record freeze-frame and live data for boost/MAP sensor B with a scan tool
Compare sensor B readings to sensor A (if present) and to expected values for engine speed/load
Visually inspect sensor, connector and wiring for damage, corrosion, or loose pins
Inspect vacuum/boost hoses and clamps for leaks, splits or disconnection
Backprobe sensor: verify 5 V reference, ground continuity, and variable signal voltage
Perform wiggle test on harness while monitoring live data for intermittent behavior

Signal parameters

Reference supply: typically +5 V from ECM (verify with DVM)
Ground: low resistance continuity to engine/ECM ground
Signal voltage (typical MAP/boost sensor): approx. 0.5 V at low pressure to ~4.5 V at high boost (varies by sensor)
At key ON engine OFF: signal often near atmospheric value (depends on sensor) — check manufacturer spec
During acceleration: signal should rise smoothly with boost; sudden drops/spikes indicate wiring/sensor fault

Diagnostic algorithm

Retrieve freeze-frame and permanent data, note conditions when code set (RPM, load, temp).
Clear code, perform road or dyno test while monitoring Boost Sensor B live data to reproduce the fault.
Visually inspect sensor location, connector and harness for heat damage, corrosion, or physical damage.
Verify vacuum/boost plumbing to the sensor. Replace cracked, collapsed or disconnected hoses and clamps.
With key ON (engine OFF) and engine running as required, backprobe sensor connector: confirm +5 V reference, good ground, and that signal voltage changes with applied pressure (use hand pump if available).
If reference or ground missing or incorrect, trace wiring to ECM; repair open/shorts, poor grounds or corroded connectors.
If wiring and power/ground are good but signal is out of range, replace Boost Sensor B. Re-test to see if code returns.
If problem persists after sensor and wiring repairs, test ECM outputs/inputs and grounds; consult manufacturer wiring diagrams and consider ECM testing/replacement.
After repair, clear codes and perform thorough road test under varied loads to confirm proper boost control and that P0240 does not return.

Likely causes

Damaged sensor B wiring harness (pinched, frayed, short to ground/5V)
Contaminated or failing boost/MAP sensor B
Poor sensor ground or weak 5 V reference from ECM
Disconnected or collapsed vacuum/boost hose to the sensor
Connector corrosion or bent pins at the sensor plug

Fault status

⚠️ Status

The powertrain control module detected that the turbo/supercharger boost sensor B circuit is providing a signal outside the expected range or performance parameters.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours