P0238 - Turbocharger/Supercharger Boost Sensor 'A' Circuit High
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
P0238 is set when the Engine Control Unit (ECU) detects a voltage signal from the Turbocharger/Supercharger Boost Sensor 'A' that remains above the calibrated limit (typically >4.8V) for a set duration. This usually indicates an open circuit in the ground wire or a short to the 5V reference in the signal wire. Because the ECU cannot accurately determine boost pressure to calculate fuel delivery, it will enter 'Limp Mode' and limit boost pressure via the wastegate or VNT actuator to prevent engine overboost and potential damage.
Possible Causes
Faulty Boost Pressure Sensor (internal short)
Wiring harness issues (open ground circuit or short to 5V reference)
Corroded or loose connectors at the sensor or ECU
Faulty Engine Control Unit (ECU) or extreme mechanical overboost condition
Symptoms
Recommended Solution
- Visual Inspection: Check the boost sensor connector for corrosion and inspect the wiring harness for chafing or damage.
- Voltage Testing: Measure the reference voltage at the connector (should be a stable 5.0V). Check ground continuity (should be near 0 Ohms).
- Signal Testing: Use a scan tool to monitor 'Live Data'. With ignition ON and engine OFF, the value should represent atmospheric pressure (approx. 100 kPa / 14.7 psi). If the value is maxed out, the circuit is likely open or shorted.
- Component Replacement: If wiring and power delivery are intact, replace the Boost Pressure Sensor.
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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