The OBD2 code P0238 is a diagnostic trouble code that signals an issue with the turbocharger or supercharger boost sensor “A” circuit, indicating that the sensor’s signal is higher than the expected range. This code is crucial in vehicles equipped with turbocharged or supercharged engines, as it can lead to symptoms like loss of power, erratic performance, and in some cases, the engine entering limp mode.
P0238 quick overview
| Meaning | P0238: Turbo/Supercharger Boost Sensor “A” Circuit High |
| Is it serious? | Yes, it can significantly affect engine performance and fuel efficiency, and lead to engine damage if ignored. |
| Possible causes | – Faulty boost pressure sensor – Wiring or connector issues in the sensor circuit – Vacuum leaks in the intake manifold or turbocharger system – Faulty turbocharger wastegate or bypass valve – Engine control module (ECM) issues |
| How to diagnose? | Inspect the boost pressure sensor and its wiring for damage or disconnections. Check for vacuum leaks using a smoke machine or visual inspection. Evaluate the turbocharger wastegate and bypass valve for proper operation. Test the sensor circuit for proper voltage and ground connections. Consider ECM diagnostic testing if other causes are ruled out. |
P0238 Meaning
The P0238 code pops up when your car’s computer thinks the turbo or supercharger is getting too much pressure, more than what it’s supposed to handle. This is like blowing too much air into a balloon; it gets stressed and can pop. In car terms, this means your engine might not run smoothly, might lose power suddenly, or could even get damaged over time.
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How to fix P0238 – learn from mechanics
I looked into P0238 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.
Case #1: Pontiac
Vehicle Information 2007 Pontiac Solstice GXP 2.0L
Issue + Repair History
- Car experiences loss of turbo boost during acceleration
- Codes: PO299 (turbo underboost), PO238 (boost sensor high voltage), PO234 (turbo overboost), PO106 (MAP sensor performance)
- Previous repair involved replacing boost pressure sensor and testing bypass and wastegate solenoids
- Symptoms occur around 4000 rpm, sometimes runs normally but intermittently loses boost
- Boost pressure sensor readings vary from 1.8 volts to nearly 5 volts during acceleration
Other OBD2 Codes + Test Results
- PO299: Turbo underboost
- PO238: Boost sensor high voltage
- PO234: Turbo overboost
- PO106: MAP sensor performance
Mechanic Suggestions
- Check intake system for leaks south of the turbo, inspect for loose or split hoses, and use a smoke machine or shop air to simulate boost
- Consider the possibility of a mis-adjusted wastegate, referencing a GM service bulletin
- Inspect the nipple on the turbocharger wastegate for damage, check all piping and clamps, and perform smoke test for leaks
- Test the turbocharger bypass solenoid valve and check for vacuum, ensuring proper operation
Final Fix
- Identified and replaced sticking wastegate solenoid, which was intermittently malfunctioning when heated, causing loss of turbo boost.
Case #2: Mercedes
Vehicle Information 2005 Mercedes-Benz C230 Kompressor 1.8L
Issue + Repair History
- Car experienced check engine light after frontal collision repair
- Conflicting codes: P2014 (adjustable cam timing solenoid short or open) and P2029 (engine speed signal implausible) from Baum scanner, P0172 (system rich bank 1) and P0238 (boost sensor A circuit high) from Snap-on scanner
- Symptoms include immediate return of codes on test drive and significant loss of engine power
- Visual inspection of cam timing solenoids and harness conducted, connections appear good
Other OBD2 Codes + Test Results
- P2014: Adjustable cam timing solenoid short or open (Baum scanner)
- P2029: Engine speed signal implausible (Baum scanner)
- P0172: System rich bank 1 (Snap-on scanner generic)
- P0238: Boost sensor A circuit high (Snap-on scanner generic)
Mechanic Suggestions
- Check harness and affected components for opens or shorts
- Consider reading codes with Mercedes DAS and performing a reset to start from scratch
- Carefully inspect intercooler hoses for looseness or disconnection, especially after collision repair
- Methodically inspect wiring harness wire by wire for any damage related to the accident
Final Fix
- Discovered a large leak in the intercooler area where the inlet pipe attached to the intercooler was not securely assembled by the body shop, allowing false air and loss of boost
- Secured the hose properly, cleared codes, and verified that acceleration performance returned to normal with no repeat of codes
- Data stream readings normalized after repair, and the car was returned to the owner by the body shop
Case #3: Volkswagen
Vehicle Information 2012 Volkswagen Jetta TDI 2.0L
Issue + Repair History
- Complaints of lack of power, glow plug light coming on, and engine going into limp mode
- Code P0238 (Manifold Pressure/Boost Sensor: Signal too High) present
- Restarting temporarily resolves issue, but problem reoccurs
- Smoke tested intake for leaks and tested wiring, found no issues initially
- Replaced Manifold Pressure/Boost Sensor previously
Other OBD2 Codes + Test Results
- P0238: Manifold Pressure/Boost Sensor (G31): Signal too High
Mechanic Suggestions
- Perform a forced regeneration on the particulate filter, as EGT sensors could also cause issues
- Check turbo actuator with Mityvac for proper extension and vacuum hold, clean turbo vanes if necessary
- Investigate for broken or pinched wires, particularly near the starter area and valve where harness wires may be stretched
- Conduct a continuity and wiggle test on the manifold pressure sensor wiring
- Consider running an overlay harness from the ECM to the sensor if wiring issues persist
Final Fix
- Discovered a harness issue where wiring was thrown enough to provide sufficient voltage but not enough for the sensor to work properly
- Replaced the harness for the pressure sensor, resolving the issue and returning engine performance to normal
How to diagnose P0238
I made you an overview of solving this DTC, based on all the advice that was suggested by certified mechanics to address this issue in previously mentioned service cases.
| Diagnostic Step | Explanation |
|---|---|
| Inspect the boost pressure sensor and wiring | Check for any physical damage or disconnections that might cause incorrect signal readings. |
| Check for vacuum leaks | Use a smoke machine to identify any leaks in the intake system that could affect pressure. |
| Evaluate turbocharger wastegate and bypass | Ensure these components are functioning correctly to maintain proper boost levels. |
| Test the sensor circuit | Verify the electrical integrity of the circuit, including voltage and ground connections. |
| Consider ECM diagnostic testing | If other diagnostics are inconclusive, assess the ECM for faults that may affect sensor data. |
In the service cases reviewed, the P0238 code was resolved through a variety of fixes, from replacing faulty wiring harnesses and securing loose intercooler pipes to addressing malfunctioning wastegate solenoids. These cases highlight the importance of thorough diagnostics to pinpoint the exact cause of boost-related issues, ensuring the turbocharged or supercharged system operates within its designed parameters for optimal performance.
Car Diagnostics Training
- Car Electrical basics
- OBD-II scanner basics
- How to use an OBD reader
- Introduction to a Bi-directional Scan tool
- OBD scanner buyer’s guide + discounts
I test OBD-II scanners and make DIY Engine diagnostics guides to help you solve your car problems without having to depend on the mechanic. A lot of them will try to scam you or are just no help at all. About Juraj Lukacko