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P0238 – Turbocharger Boost Sensor A Circuit High (OBD2)

P0238 means "Turbocharger Boost Sensor A Circuit High". The voltage in the boost pressure sensor circuit is above the permitted maximum. For most sensors this points to an open signal or ground wire – the signal "floats" up to the reference voltage – or to a short to voltage.

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P0238 quick summary

Fault codeP0238
MeaningTurbocharger Boost Sensor A Circuit High
SystemPowertrain (Engine & Transmission)
VehiclesGeneric OBD2
SeverityMedium
Can I drive?Usually yes, in limp mode. With an overboost code, avoid full throttle – excessive boost can damage the engine and turbo.
Repair cost€30 – €1,500

How the boost pressure sensor works

The boost pressure sensor measures the pressure the turbocharger produces so the engine control unit can regulate boost and protect the engine; P0234 means boost has exceeded the safe limit.

The boost pressure sensor sits in the charge air pipe or intake manifold after the intercooler, often combined with an air temperature sensor. It works like a MAP sensor with a wider range: a 5 V reference, ground and a signal that rises with pressure.

The control unit compares the measured boost with the target. If the signal is electrically out of range, implausible, or boost goes above the safe limit (overboost, P0234), it reduces power to protect the engine and turbo. Sensor B codes refer to a second sensor on engines with two turbochargers or two measuring points.

Oil mist from the crankcase ventilation and turbo seals often contaminates the sensor; boost leaks, sticking wastegates or vanes and faulty control solenoids cause range and overboost codes.

On VAG vehicles (VW, Audi, Škoda, Seat, Cupra), VCDS and older VAG testers can show this code as the five-digit VAG code 16622 (P0238). Both numbers mean the same fault.

Symptoms of P0238

  • Limp mode, loss of power
  • Check Engine light on
  • Surging power or sudden power cut under acceleration (overboost)
  • Black smoke
  • Turbo or boost control codes alongside

Most common causes of P0238 (most likely first)

Mechanic's Pro Tip

If boost and barometric pressure differ by more than about 50 mbar with the engine off, the boost sensor is faulty. If they agree and the code persists, look at the turbo control instead.

  1. 1.Open circuit in the signal or ground wire

    Most likely

    A loose ground connection is a very common cause.

  2. 2.Signal wire shorted to the 5 V reference or battery voltage

  3. 3.Faulty boost pressure sensor

  4. 4.Oily or contaminated boost sensor

  5. 5.Wiring fault or 5 V reference problem

  6. 6.Sticking turbo vanes or wastegate (overboost)

Step-by-step diagnostic guide

  1. 1

    Read codes and compare pressures

    Read all codes. With the engine off, the boost sensor should read the same as the barometric pressure.

  2. 2

    Check signal and ground

    With the ignition on and the boost pressure sensor plugged in, back-probe the signal and ground wires. A signal stuck at reference or battery voltage points to an open ground/signal wire or a short to voltage.

    Multimeter: Ground wire to battery negative: below about 0.1 V. Signal stuck at about 5 V (or 12 V) = open or short to voltage.

  3. 3

    Inspect and clean the sensor

    Remove the sensor, check it for oil and clean it carefully with electrical contact cleaner.

  4. 4

    Check reference, ground and signal

    Measure the 5 V reference and ground and watch the signal rise smoothly with boost.

    Multimeter: Key on, engine off: equal to barometric pressure (about 1,000 mbar near sea level).

  5. 5

    Log specified vs actual boost

    During a full-load acceleration, compare specified and actual boost. Actual boost overshooting the target points to a sticking wastegate or vanes.

  6. 6

    Repair and verify

    Replace the sensor or fix the boost control fault, clear codes and repeat the test drive.

Frequently asked questions

Can I keep driving with P0238?

Usually yes, in limp mode. With an overboost code, avoid full throttle – excessive boost can damage the engine and turbo.

How much does it cost to fix P0238?

Typical repair costs are 30 € – 1500 €, depending on the cause and the vehicle. The most common fixes are: open circuit in the signal or ground wire; signal wire shorted to the 5 V reference or battery voltage; faulty boost pressure sensor. Always confirm the cause with the tests above before buying parts.

What causes overboost (P0234)?

Usually a wastegate or VTG vanes that do not open, a faulty boost control solenoid or a cracked vacuum hose. Less often a faulty boost sensor reading too high.

Is the boost sensor the same as the MAP sensor?

On many turbo engines yes – the MAP sensor in the intake manifold measures boost. Some engines have both.

What is the difference between P0238 and similar codes?

P0238 belongs to a group of codes for the same component that differ in the type or location of the fault: P0235 – Turbocharger Boost Sensor A Circuit Malfunction; P0236 – Turbocharger Boost Sensor A Circuit Range/Performance; P0237 – Turbocharger Boost Sensor A Circuit Low; P0239 – Turbocharger Boost Sensor B Circuit Malfunction; P0240 – Turbocharger Boost Sensor B Circuit Range/Performance; P0241 – Turbocharger Boost Sensor B Circuit Low. The tests on this page apply to the whole group; the type of fault tells you where to start.

Related fault codes

This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.