Turbocharger Boost Sensor B Circuit Low
The turbocharger's boost pressure sensor is sending a voltage signal that's too low, like a fuel gauge needle stuck near empty. The engine computer can't accurately read how much boost pressure the turbo is creating.
The ECU monitors the analog voltage output from the boost sensor B circuit, which should rise as turbo pressure increases. When voltage drops below the minimum expected threshold, the ECU triggers this fault code. The sensor typically operates between 0.5V and 4.5V depending on boost pressure.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Boost Sensor B Voltage | 0.5V to 4.5V (increases with boost) | Below 0.5V or open circuit |
| Boost Pressure | 0 to 30+ PSI | Sensor reading below minimum expected |
Code P0242 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P0242 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.