The engine computer has detected that the signal from the turbocharger or supercharger boost pressure sensor "B" is outside of the expected normal operating range. This typically points to an issue with the sensor itself, its wiring, or a physical boost leak, rather than a failure of the turbocharger.
The sensor itself has degraded or failed internally, causing it to send an out-of-range voltage signal to the engine computer.
Corroded pins, chafed wires, or a loose connection can disrupt the signal voltage, causing the computer to see an erratic or out-of-range reading.
A tear in a boost hose or a leaking intake gasket can cause actual manifold pressure to fall outside expected parameters, triggering a range/performance code.
If the mechanical components controlling boost pressure fail to operate correctly, the resulting pressure may not match what the computer commands.
An internal fault in the PCM preventing it from accurately reading the 5-volt reference or signal return. This is extremely rare and should only be considered after all other components are verified.
The vehicle may be drivable, but you will likely experience reduced power and poor fuel economy. Prolonged driving with incorrect boost pressure can potentially damage the catalytic converter if the engine runs too rich.
Replacing the sensor is the most common fix, but wiring issues or physical boost leaks are also highly likely. It is best to test the sensor and wiring before replacing any parts.
It is very rare for the PCM to cause a P0240 code. Some technicians wrongly recommend replacing the PCM without thoroughly testing the sensor and wiring; a control-module failure should be the absolute last resort.
While a failing turbocharger can cause actual boost pressure issues, the P0240 code specifically refers to the electrical circuit range and performance of the sensor. The sensor, wiring, or a boost leak are much more likely culprits.