P0238: Turbocharger/Supercharger Boost Sensor "A" Circuit High
The boost pressure sensor signal is above its normal range.
Normal risk
Usually drivable, but power is often limited. Have it checked soon.
Short answer · Can I keep driving with P0238?
Usually yes, but expect reduced power because the engine cannot control boost without a reliable reading. Have it checked soon.
What does P0238 mean?
P0238 means the boost pressure sensor signal is above the range a working sensor produces. A short to voltage, an open ground or a failed sensor are typical causes. The boost pressure sensor sits in the intake after the turbocharger and intercooler; on many engines it is the same part as the manifold pressure sensor or is combined with an air temperature sensor.
What the car does when the code is set
The check engine light comes on. The engine uses a substitute value, so it may hesitate, idle unevenly, use more fuel or produce black smoke. On turbo engines, power may be limited.
How the system works
The manifold absolute pressure (MAP) sensor measures the pressure, or vacuum, in the intake manifold. Low pressure means low engine load; high pressure means high load or boost. The engine control unit uses it to calculate load and fuel quantity, and on turbo engines to control boost. The sensor sends a voltage that rises with pressure; with the engine off, the reading should match outside air pressure.
Common symptoms
Possible causes
Listed without ranking. The cause on your car depends on make, engine and mileage — see the maker notes below.
- Split or disconnected vacuum hoseThe sensor reads manifold pressure through a small hose or port; a leak or loose hose gives a wrong reading.
- Intake leakAir leaking past a gasket or hose changes manifold pressure and the fuel calculation.
- Dirty or oily sensorOil vapour from the crankcase ventilation can coat the sensing element.
- Wiring or connector faultA broken wire, corrosion or a poor reference voltage changes the signal.
- Failed sensorThe sensor itself can drift or fail with age.
How it is diagnosed
- Check the hose and connectorMake sure the sensor is firmly connected and any vacuum hose to it is intact and not blocked.
- Compare the reading with the engine offWith the ignition on and the engine stopped, manifold pressure should be close to the barometric pressure for your altitude.
- Look for intake leaksA smoke test finds leaks in the intake manifold, hoses and gaskets.
- Measure supply, ground and signalA workshop checks the reference voltage and signal at the connector against the service data.Do not pierce wire insulation to take readings; it lets moisture in and causes new faults.
Questions about P0238
Can I clean a boost pressure sensor?
Sometimes. Oil from the crankcase breather can coat the sensor and slow it down. A careful clean with sensor-safe cleaner can help, but if the code returns or the readings are still wrong, the sensor should be replaced.
Is the MAP sensor the same as the MAF sensor?
No. The MAP sensor measures pressure in the intake manifold, the MAF sensor measures the air flow entering the engine. Some engines use both.