OBD CodesWhat it means
A turbocharger pushes extra air into the engine. The computer controls how much pressure, or boost, it makes. These codes mean the boost is higher or lower than commanded, or a sensor or control valve in the boost system has an electrical fault.
Codes in this group
| Code | Meaning |
|---|---|
| P0234 | Boost pressure too high (overboost) |
| P0235 | Boost pressure sensor A circuit fault |
| P0236 | Boost pressure sensor A reading out of range |
| P0237 | Boost pressure sensor A signal low |
| P0238 | Boost pressure sensor A signal high |
| P0243 | Wastegate control valve A circuit fault |
| P0244 | Wastegate control valve A out of range |
| P0245 | Wastegate control valve A signal low |
| P0246 | Wastegate control valve A signal high |
| P0299 | Boost pressure too low (underboost) |
Bank 1 is the side of the engine that has cylinder 1. Sensor 1 is before the catalytic converter and sensor 2 is after it. More terms explained.
What you may notice
- Clear loss of power (underboost) or surging (overboost)
- Whistling or hissing under acceleration
- Limp mode
- Black smoke on a diesel
Common causes
Most likely first:
- A split or loose intercooler hose or clamp
- A sticking wastegate or variable-vane mechanism, often from soot
- A leaking or failed boost control valve or its vacuum hoses
- A faulty boost pressure sensor
- A worn turbocharger
What to check first
- Look along the large air hoses from turbo to intercooler to engine for oil mist, splits or a popped clamp
- Listen for a new hiss when accelerating
- Drive gently: hard use with a boost fault can damage the turbo or engine
Have a mechanic confirm. A fault code tells you which system reported a problem, not which part has failed. The same code can have several causes, and they differ between car models. Use this page to understand the code, then have a qualified mechanic test the car before any part is replaced.
After the repair
Once the cause is fixed, the code can be cleared with a scan tool, or the warning light goes out by itself after several trips without the fault. Clearing a code without fixing the cause only hides it for a while. More about clearing codes.
Related codes
Mass air flow (MAF) sensor (P0100), Manifold pressure (MAP) and barometric sensor (P0105), Intake air temperature sensor (P0110), Engine coolant temperature sensor (P0115), Thermostat and engine warm-up (P0125), Throttle position sensor (P0120), Accelerator pedal sensor and throttle agreement (P2120), Electronic throttle actuator (P2100). All codes.
Written in November 2026. These are generic OBD-II codes, the same on all makes. Causes and repair steps differ between models.