P0238: Turbocharger/Supercharger Boost Sensor "A" Circuit High

P0238 means the voltage from the boost pressure sensor has risen above the maximum the ECU accepts, typically above about 4.5 to 4.9 V. The ECU reads that as an impossibly high boost pressure, ignores the sensor and usually limits power. Unlike P0234, it does not mean the turbo is really overboosting: it is almost always an electrical fault such as an unplugged or failed sensor, a broken ground or a signal wire shorted to voltage. Most repairs cost between 40 and 220 euros.

P0238 is a fuel system-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0238 and illuminates the check engine light.

If your vehicle has triggered P0238, you may notice one or more of these symptoms:

• Check engine light on
• Limp mode or a reduced power warning, often immediately after starting or on the first acceleration
• Very weak acceleration because boost is cut back to a minimum
• Live data showing a boost reading far above atmospheric pressure with the engine off
• Other sensor codes at the same time if a shared 5 V reference is shorted
• Fault that comes and goes over bumps if the connector or harness is damaged

Here are the most common causes of P0238:

No - address this immediately. A signal stuck at the top of the scale tells the ECU that boost is extremely high, so most engines cut power into limp mode straight away or the moment you accelerate. That makes overtaking and motorway merging unsafe. Drive gently to a workshop without heavy throttle; the engine is usually protected, but you will have little power when you need it.

Follow these steps to pinpoint the root cause of P0238:

1. Read all stored codes. If P0238 sits alongside other high-input sensor codes, suspect a shared 5 V reference or ground rather than the boost sensor itself. If P0234 is also stored, check whether boost was really high before blaming the sensor
2. With the ignition on and the engine off, read the live boost value where the ECU exposes it on a generic OBD2 reader, or the MAP reading on engines that share one sensor. With no boost in the system it should read atmospheric pressure, roughly 95 to 105 kPa at sea level. A reading pinned far above that, often at the top of the sensor's range, confirms the signal really is high
3. Inspect the sensor and connector. Check that the plug is fully clicked home, look for corrosion, water or oil inside it, and look for pins that have pushed back. Follow the harness for chafing where it runs near the turbo, brackets or the charge pipe
4. Unplug the sensor and, with the ignition on, bridge the signal pin to the sensor ground pin at the connector with a fused jumper while watching the live value. If the reading drops to the bottom of the scale and the fault turns into the circuit low code, the signal wire and the ECU are fine, and the sensor or its ground is the problem. If it stays high, the signal wire is shorted to voltage somewhere between the plug and the ECU
5. With the sensor plugged back in, back-probe the reference and ground. The reference should read about 4.5 to 5.2 V and the ground within about 0.1 V of battery negative. A reference at battery voltage means a short to 12 V; a ground well above 0.1 V means an open or corroded ground
6. Fit the correct sensor for the engine and confirm the reading returns to atmospheric pressure with the key on. Then clear the code and road test, watching the boost value rise smoothly under load

Repair costs for P0238 vary depending on the root cause and your vehicle. Here are typical estimates:

P0238 behaves differently depending on your vehicle. Select your car below for model-specific causes and known issues:

These codes are often seen alongside P0238 or indicate related issues: