Diagnostic Trouble Code (DTC) P0242 Turbocharger/Supercharger Boost Sensor B Circuit High is a generic code applicable to most vehicles equipped with a turbocharger, including brands such as VW, Dodge, Mercedes, Isuzu, Chrysler, Jeep, etc.
Boost System Operation
The Powertrain Control Module (PCM) regulates turbocharger pressure via a boost solenoid. To adjust this pressure, the PCM monitors in real-time the data sent by the boost pressure sensor.
How Does the Boost Sensor Work?
This sensor acts as a variable resistor:
- The PCM sends a 5V reference signal to the sensor.
- When pressure is low, resistance is high → only a low voltage (approximately 0.5V) is returned to the PCM.
- When pressure increases, resistance decreases → the voltage returned to the PCM increases (up to 4.5V at maximum boost).
Code P0242 triggers when the PCM detects a voltage above 4V on the sensor “B” circuit, while no boost is requested.
Common Symptoms
When this code appears:
✅ Check Engine Light (CEL) illuminates.
✅ The PCM enters limp mode (limited boost and timing).
✅ Noticeable loss of power (vehicle in “safe mode”).
⚠️ Risk of catalytic converter damage if the problem persists.
Possible Causes
1️⃣ Other associated DTCs (e.g., faulty IAT sensor, ECT sensor, or 5V circuit).
2️⃣ Wiring problem (damaged wires, corroded connectors).
3️⃣ Faulty boost sensor “B”.
4️⃣ Short to voltage in the sensor circuit.
5️⃣ Faulty PCM (less common).
Diagnostic Procedures
🔧 1. Check Technical Service Bulletins (TSB)
Some vehicles have known issues with solutions published by the manufacturer.
🔧 2. Inspect for intermittent faults (wiggle test)
- With engine running, gently shake the sensor harness to detect poor contact.
🔧 3. Electrical measurements (digital multimeter)
- KOEO (Key On, Engine Off):
- Disconnect the sensor → check for 5V on the supply.
- If 5V is absent → PCM or circuit problem.
- Sensor connected:
- Normal KOEO voltage ≈ 0.5V. If abnormal → faulty sensor.
⚠️ To avoid:
❌ Do not use an incandescent test light (risk of damaging the circuit).
Conclusion
Code P0242 indicates a high voltage signal problem with the boost sensor. A methodical check of the wiring, sensor, and associated codes is essential to resolve the issue effectively. If the diagnosis is uncertain, further analysis with a specialized scan tool may be necessary.
🚗 Recommended quick solution: Replace the faulty sensor or repair the circuit as needed.