Drivable short-term in limp mode; fix soon. P0238 means the engine computer saw the turbocharger (or supercharger) boost-pressure sensor 'A' signal sitting too high, above its normal working range. It is an electrical circuit fault, usually a signal wire shorted to voltage, an open ground, or a failed sensor, not necessarily too much actual boost.
What P0238 means
A forced-induction engine uses a boost-pressure sensor to tell the powertrain control module (PCM) how much pressure the turbo or supercharger is building in the intake tract. On many engines this is a dual-function pressure and temperature unit mounted in the charge-air tube between the intercooler (charge air cooler) and the throttle body. It is typically a three-wire sensor fed a 5-volt reference, returning a signal that rises with pressure and sharing a ground. P0238 sets when the PCM reads the boost-sensor signal voltage above its expected ceiling, near reference voltage, which the module interprets as an out-of-range 'circuit high' condition. In electrical terms that points to the signal wire shorted to a voltage source, an open or high-resistance ground so the signal floats high, or a sensor that has failed internally and pins its output high. It is monitored with the key on and engine off, key on and engine running, and continuously, and typically forces reduced-power fail-safe operation so boost is limited until the fault clears.
Symptoms
- Check-engine light on, often with the code stored as continuous memory
- Reduced engine power or a limp/fail-safe mode that caps boost
- Poor throttle response and hesitation, especially under acceleration
- Noticeably weak or absent turbo/supercharger boost and slow pickup
- Possible rough running or occasional stumble under load
Common causes
- Failed turbocharger/charge-air boost-pressure sensor pinning its signal high
- Signal wire shorted to voltage (to the 5V reference or battery positive)
- Open or high-resistance ground on the sensor circuit letting the signal float high
- Corroded, loose, or damaged sensor connector or chafed/pinched harness wiring
- Moisture or oil intrusion in the connector causing an electrical bridge
- Rarely, a PCM/driver fault or reference-voltage problem on the shared circuit
Severity & driving advice
Severity: Moderate — Not an immediate hazard, but the engine usually drops into reduced-power limp mode and boost is capped until the sensor circuit is fixed.
Can I drive? Drivable short-term in limp mode; fix soon.
Diagnostic approach
- Read codes and check live boost-sensor data — Scan for all stored and pending codes and note freeze-frame conditions. With a scan tool, watch the boost/charge-air pressure sensor's live voltage and pressure reading. Key-on engine-off it should sit near barometric pressure with a low-to-mid signal voltage; a value stuck near the 4.9-5.0V reference ceiling, or reading full-scale pressure with the engine off, confirms a circuit-high condition rather than genuine overboost.
- Inspect the sensor, connector, and wiring — Locate the boost-pressure sensor in the charge-air tube between the intercooler and throttle body. Unplug it and inspect for corrosion, bent or spread terminals, moisture, or oil. Follow the harness looking for chafing, pinches, or melting near hot components. A backprobe of the connector while wiggling the harness can expose an intermittent short-to-voltage that sets the code.
- Test the reference, ground, and signal circuits — Key on, verify about 5 volts on the reference wire and a good ground (near 0V) at the sensor connector. With the sensor unplugged, the signal wire should read near 0V; if it reads high or near reference voltage disconnected, the signal is shorted to voltage upstream. Check continuity of the ground circuit back to the PCM, since an open ground makes the signal float high.
- Substitute a known-good sensor value — If the wiring, reference, and ground all check out, the sensor is the likely fault. Confirm with a known-good sensor or by verifying the signal responds correctly to applied vacuum/pressure. Compare the sensor's voltage-versus-pressure behavior to spec: signal should climb smoothly with pressure, not jump to the ceiling.
- Clear, road-test, and confirm the repair — After repair, clear the code and drive the vehicle through a boost cycle while monitoring the sensor voltage and reported boost. Confirm the signal tracks actual manifold/charge pressure and that fail-safe/limp mode no longer engages. Recheck continuous-memory codes to be sure P0238 does not reset.
Make & model notes
Ford: On EcoBoost engines such as the 3.5L twin-turbo (F-150), Ford calls it the turbocharger boost pressure (TCBP)/charge air cooler temperature (CACT) sensor, a dual pressure-and-temperature unit in the intake tube between the charge air cooler and throttle body. Ford's description ties P0238 to an open circuit or high voltage in the TCBP circuit; its pinpoint test targets the sensor, its connector, and short-to-voltage in the harness. Check the connector and routing for damage before condemning the sensor.
Volkswagen: On VW and Audi turbo (TSI/TFSI) engines the equivalent charge-air/boost-pressure sensor sets a comparable circuit-high fault. Inspect the sensor in the charge-air pipe, its connector, and the reference and ground wiring; oil or moisture in the boost plumbing and connector corrosion are common triggers on these engines.
FAQ
Does P0238 mean my turbo is bad?
Usually not. P0238 is a boost-pressure sensor circuit fault, meaning the sensor's signal read too high electrically. It points at the sensor, its connector, or the wiring far more often than at the turbocharger itself. Diagnose the circuit before replacing any hardware.
Can I drive with a P0238 code?
You can usually drive short distances, but the engine typically drops into reduced-power fail-safe mode with limited boost, so it will feel sluggish. It is not an immediate safety hazard, but you should have the sensor circuit repaired soon so normal power and boost control return.
What is the difference between P0237 and P0238?
They are the two out-of-range ends of the same boost-sensor circuit. P0237 is 'circuit low' (signal too low, often a short to ground or open reference), while P0238 is 'circuit high' (signal too high, typically a short to voltage or open ground). Both usually cap boost until repaired.
How do I test the boost-pressure sensor for P0238?
With a scan tool, watch the sensor's live voltage and pressure with the key on. Then confirm about 5 volts of reference and a clean ground at the connector, and check that the signal wire is not shorted to voltage. If the wiring and grounds are good but the signal stays pinned high, the sensor is the likely fault.