P0238 — Turbocharger/Supercharger Boost Sensor “A” Circuit High #

Note: The code label or wording may vary depending on the vehicle manufacturer.

• Turbocharger Boost Sensor “A” Circuit High (Ford, GM, Honda, Toyota, FCA, BMW, Mercedes-Benz, Volkswagen, Audi, Hyundai, Kia, Nissan)
• Supercharger Boost Sensor “A” Circuit High (Jaguar, Land Rover, Mercedes-AMG, Ford Mustang Shelby, GM Performance)
• Manifold Absolute Pressure/Boost Sensor “A” Circuit High (Various OEMs)

Code P0238 Summary #

Diagnostic Trouble Code (DTC) P0238 indicates that the engine control module (ECM) or powertrain control module (PCM) has detected a signal from the boost pressure sensor “A” that is higher than the expected range. This sensor, also known as the turbocharger boost sensor or manifold absolute pressure (MAP) sensor in some systems, helps the computer monitor intake air pressure generated by the turbocharger or supercharger. When the sensor’s voltage reading is too high compared to what the ECM expects, the system triggers this code. This malfunction can affect both performance and emissions, and typically requires immediate attention. While the wording may change between OEMs, the underlying problem is a signal that is “too high” from the boost sensor circuit.

Common Symptoms for Code P0238 #

When P0238 is present, your vehicle may experience a range of symptoms, mostly tied to engine performance and drivability. Often, the check engine light will come on, but the effects can be more noticeable, especially under load or acceleration. Be alert for the following:

• Illuminated Check Engine Light (CEL or MIL)
• Reduced engine power (limp mode)
• Poor acceleration or hesitation under boost
• Unusually high or fluctuating boost gauge readings (if equipped)
• Black smoke from the exhaust under load
• Possible engine knocking or pinging
• Decreased fuel efficiency

Most Likely Causes for P0238 #

P0238 is typically triggered by electrical or sensor-related issues. The most frequent causes, ranked by likelihood, include:

1. Faulty boost pressure sensor (“A”) — The sensor itself may be malfunctioning or internally shorted.
2. Wiring or connector problems — Damaged, shorted, or corroded wiring/connectors in the sensor circuit.
3. Sensor circuit short to voltage — A wire in the harness is contacting a voltage source, causing a higher than normal signal.
4. PCM/ECM malfunction — Rare, but possible if all else checks out.
5. Aftermarket tuning or modifications — Incorrectly installed boost controllers, piggyback ECUs, or performance chips can disrupt signal integrity.
6. Incorrect sensor installation or swapped connectors — Especially after recent repairs.

Step-by-Step Diagnostic for P0238 #

Properly diagnosing P0238 requires a systematic approach. Skipping steps can lead to misdiagnosis or unnecessary parts replacement. Here’s a master tech’s method:

1. Verify code presence: Use an OBD-II scanner to confirm P0238 is active. Clear the code and see if it returns after a short drive.
2. Visual inspection: Check the boost sensor and its wiring for obvious damage, corrosion, or improper connections.
3. Check sensor voltage: With the key on, engine off, monitor the sensor’s signal voltage using a scan tool or multimeter. Typical range is 0.5–4.5V; readings above 4.5V indicate a problem.
4. Inspect wiring harness: Look for chafed, pinched, or oil-soaked wires. Pay special attention to areas near hot exhaust components or sharp engine edges.
5. Test sensor ground and reference voltage: Ensure the sensor is receiving a proper 5V reference and solid ground from the PCM/ECM.
6. Substitute a known-good sensor: If possible, swap in a working sensor and observe if the code clears.
7. Check for PCM/ECM updates or TSBs: Some manufacturers release technical service bulletins (TSBs) for known issues related to boost sensor circuits.

Possible Repairs for P0238 #

Once you’ve pinpointed the cause, repairs should address the root of the signal issue. The most common fixes include:

• Replace the boost pressure sensor (“A”) if faulty or out of specification.
• Repair or replace damaged wiring or connectors in the sensor circuit.
• Correct any short circuits to voltage or ground in the harness.
• Reinstall or re-pin sensor connectors if they are loose or corroded.
• Remove or correctly install aftermarket tuning devices that may affect the sensor circuit.
• Update or reflash the PCM/ECM if a TSB applies or if recommended by the OEM.
• Replace the PCM/ECM only after all other possibilities have been ruled out—this is rare.

Is It Safe to Drive with Code P0238? #

Driving with code P0238 is not recommended for extended periods. While the vehicle may still run, performance will be compromised, and you risk damaging the engine or turbocharger if the underlying cause is severe. If the car enters limp mode, power will be significantly limited to protect critical components. A short drive to a repair facility is usually acceptable, but continued use without diagnosis can lead to more expensive repairs or emissions failures.

Vehicles Most Commonly Affected by P0238 #

This code appears on a wide range of modern turbocharged or supercharged vehicles, including both gasoline and diesel engines. Models frequently affected include:

• Ford F-150 EcoBoost, Focus ST/RS, Mustang EcoBoost
• Chevrolet Silverado, Cruze, Malibu Turbo, GM Duramax diesels
• Volkswagen Golf/GTI, Jetta TSI/TDI, Audi A4/A3 Turbo
• BMW 3 Series/5 Series Turbo, X1/X3/X5
• Mercedes-Benz C-Class/E-Class Turbo, AMG models
• Hyundai Sonata/Kia Optima Turbo
• Nissan Juke, Altima Turbo, Titan XD Diesel
• Toyota Supra, Lexus IS Turbo
• Honda Civic/Accord Turbo
• Ram 1500 EcoDiesel, Jeep Grand Cherokee Diesel

Common Mistakes & Best Practices with P0238 #

Avoid these pitfalls when working with P0238. Best practices can save you time and money:

• Mistaking a wiring fault for a sensor failure — Always test the sensor and wiring before replacement.
• Ignoring aftermarket modifications — Performance mods can cause signal irregularities; always return to stock for diagnosis.
• Overlooking ground and 5V reference circuits — Faulty grounds or reference voltage can skew sensor readings.
• Skipping a visual inspection — Many issues are caused by physical damage or loose connectors.
• Forgetting to check for TSBs — OEMs may have published fixes or software updates for recurring issues.

Quick FAQ for Code P0238 #

Here are fast answers to the most common questions about P0238:

• Q: Can a dirty air filter cause P0238?
  A: No, a clogged filter may reduce airflow but does not cause a high circuit voltage. Focus on the sensor and wiring.
• Q: Is it safe to clear the code and keep driving?
  A: Clearing the code may reset the light, but the underlying problem will likely return. Proper diagnosis is necessary to avoid further issues.
• Q: Will this code affect my vehicle’s emissions test?
  A: Yes, P0238 will cause a failed readiness monitor and likely result in an emissions test failure.