What it means
The boost pressure A signal voltage is above the upper diagnostic threshold — short to supply voltage or defective sensor.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
Boost pressure sensor A measures pressure in the turbocharger or supercharger air path and sends a signal to the control module. P0238 sets when the signal rises above the module’s upper electrical threshold, which can be caused by a short to supply voltage or a defective sensor.
Common causes
Most likely first.
- Sensor circuit shorted to supply voltage
- Boost pressure sensor failed
- Connector pins corroded - high contact resistance
Symptoms
- Check engine light on
- Significant power loss / limp mode
- Possible blue or black smoke from exhaust
- Whistling or hissing sound from intake
How to diagnose it
- Record freeze-frame data and check scan-tool data for boost sensor A to confirm whether the fault appears with the engine off or only while running.
- Inspect sensor A’s connector and wiring for corrosion, loose or pushed-back pins, damaged insulation, and contact with a power wire.
- Using the wiring diagram, check whether the signal wire is shorted to a supply circuit and verify the sensor’s ground and reference circuits.
- With the circuit safely isolated, test the signal wire for unwanted continuity to supply and compare results with the manufacturer’s specification.
- If the wiring tests correctly, check sensor A’s output and circuit operation using the manufacturer’s diagnostic procedure.
Common fixes
- Repair damaged wiring that shorts the sensor A signal to a power supply.
- Clean, secure, or repair poor connections at the boost sensor A connector.
- Replace boost pressure sensor A if it produces an out-of-range signal despite a sound circuit.
- Repair a module fault only after the sensor and wiring have been tested.
Can I keep driving?
If the vehicle is in limp mode or has reduced power, avoid overtaking, towing, and hard acceleration until the signal fault is fixed. Stop if heavy smoke, rough running, or severe power loss makes the vehicle unsafe to control.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.