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P0291 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


Let’s start with the basic definition, before looking at more detail. A standard system used in the vehicle for identifying and communicating problems within various systems is DTC codes, or OBD OnBoard Diagnostics (IIOBDI codes). One such code is P0291, and it concerns problems with the turbocharger or supercharger system.


P0291 specifically indicates a “Turbocharger/Supercharger ‘A’ Overboost Condition.” In simpler terms, this is the result of a turbocharger or supercharger in your vehicle giving excessively high boost pressure and exceeding established operating parameters. In a twin-turbo system, ‘A’ in the code is usually used to designate the primary turbochargers.


Effective troubleshooting requires knowledge of the P0291 DTC code’s causes. Typical reasons include

  • Wastegate Issues: There may be a problem with the wastegate, which regulates boost pressure.
  • Wastegate Stuck Open: A stuck open wastegate might result in over-boost circumstances.
  • Vacuum Leaks: Boost control may be impacted by any vacuum leaks in the system.
  • Issues with the Boost Control Solenoid: Overboost circumstances can be brought on by boost control solenoid issues.
  • Faulty Sensors: Issues with sensors that monitor the turbocharger’s performance can lead to this code.


Recognizing the symptoms that accompany a P0291 code can help you identify the issue sooner. Common symptoms include:

  • Reduced Engine Power: Your vehicle may go into a reduced power mode to prevent damage.
  • Check Engine Light: The most obvious sign is the illuminated check engine light on your dashboard.
  • Reduced Fuel Economy: Overboost circumstances may cause a reduction in fuel economy.
  • Whistling or Hissing Sounds: The engine may make odd whistling or hissing sounds.


A P0291 code is often diagnosed by:

  • Code retrieval: Get the code with an OBD-II scanner.
  • Visual inspection: Look for obvious problems with the turbocharger/supercharger system.
  • Wastegate Inspection: Verify that the wastegate is operating correctly.
  • Testing for Vacuum Leaks: Check the system for vacuum leaks.
  • Testing of Sensors and Control Solenoids: Check the functionality of the sensors and control solenoids.

Common mistakes

Avoid making the following errors when handling a P0291 code:

  • Ignoring It: Ignoring the error code may result in more serious problems and perhaps engine damage.
  • Replacing Parts Without Diagnosis: Avoid replacing parts without proper diagnosis, as this can be costly and ineffective.

How serious is this?

The seriousness of the P0291 code is determined by what constitutes this problem, and how to address it. If you ignore it, your vehicle’s performance can be reduced, its fuel efficiency decreases, and damage to the engine may occur.

What repairs can fix the codeS?

repair manuals

To fix a P0291 code, you may need to:

  • Repair or Replace the Wastegate: If it’s faulty or stuck open.
  • Fix Vacuum Leaks: Address any vacuum leaks in the system.
  • Replace Sensors or Solenoids: If they are malfunctioning.
  • Check and Adjust Boost Pressure: Ensure boost pressure is within acceptable limits.

Related codes

It’s essential to be aware of related codes, such as P0290 (Turbocharger/Supercharger ‘A’ Control Circuit Low) and P0292 (Turbocharger/Supercharger ‘A’ Overboost Condition).


Finally, an over-boost condition for the turbocharger or supercharger system of your vehicle is indicated by the P0291 DTC code. Failure to address this issue or misdiagnose it can have detrimental effects on performance and efficiency. To maintain the smooth operation of your vehicle, you should take this code with due seriousness, diagnose it accurately, and immediately correct the underlying problem. If you’re not confident in your diagnostic and repair skills, consult a professional mechanic to resolve the issue effectively and prevent further damage to your vehicle.

P0291 Code – What Does It Mean & How To Fix It