P0238: Turbocharger Boost Sensor B Circuit High

What does P0238 actually mean?

On engines with a second boost pressure sensor, this code sets when sensor B's signal voltage reads above the maximum value the computer expects across the operating range. It points to an open circuit or a short to a higher reference voltage rather than a real pressure spike, since that pressure would not be physically possible.

The code sits in the turbocharger boost control area and is reported by the comprehensive component monitor. It names the circuit or the condition where the computer saw a reading outside its expected range. It does not name a failed part, and several genuinely different faults set this same code, which is the whole reason the causes below are ordered rather than listed.

What people usually notice

• Reduced power under boost
• Check engine light
• Sluggish acceleration
• No unusual noise

Why does P0238 set?

The causes below are ordered by how often they turn out to be the answer, cheapest and most common first. That order matters more than the list itself: the expensive component named in the code text is very rarely the first thing to replace, and working down from the top is what stops a turbocharger boost control fault becoming an expensive guess.

Open circuit in the sensor B signal wire is the one to rule out before anything else. A broken wire is the most direct cause of a signal stuck high.

The order worth checking on P0238

Start with freeze frame. Engine load and RPM at the fault show under what condition the high reading occurred. That snapshot is taken at the instant the code set, and it is the single most useful piece of evidence you have, which is also why clearing the code before reading it is such a costly habit.

This code is diagnosed by watching values change rather than by reading the number again, so the tool has to stream live data and hold freeze frame. Checking live sensor B voltage at key on and under boost confirms whether the signal is pinned high or missing entirely.

The order worth working in

• 1. Open circuit in the sensor B signal wire: A broken wire is the most direct cause of a signal stuck high.
• 2. Short to a reference voltage wire in the harness: A chafed wire touching a reference wire pushes the signal high.
• 3. Corroded ground connection for the sensor: A poor ground can push the sensor's reading high.
• 4. Failed sensor B element: The sensor element itself can open internally with age.
• 5. Damaged connector pin at the sensor: A bent or corroded pin can produce the same fault as a wiring break.

Is it safe to drive with P0238?

Boost may default to a conservative level, which is safer but can feel weak, so drive gently until it is repaired.

This is a severity 2 of 4 code. It will not usually strand you, but it will fail an emissions test while it is present, and the underlying fault rarely gets cheaper by being left alone.

What does it cost to ignore P0238?

Running on the computer's conservative fallback boost strategy costs noticeable power and fuel economy until the sensor circuit is repaired.

There is also the diagnostic cost of waiting. Freeze frame data, pending code history and the readiness monitor state all describe the fault as it was when it set, and all of it is lost the moment somebody clears the code to make the lamp go out.