Skip to content

P0299 Fault Code: Turbo/Supercharger Underboost (Causes & Fixes)

  • by
  • 3 min read

Last Updated on: 19th November 2023, 10:49 pm

P0299 OBD fault code stands for: Turbocharger/Supercharger “A” Underboost Condition

This DTC is issued when the vehicles supercharger or turbocharger is generating a low or insufficient boost pressure, called under-boost, reducing the engine’s power output.

If the boost pressure does not reach the pre-determined pressure level, the vehicle may go into a “limp mode”, protecting the engine from damage by reducing RPMs, power, and engine performance.

This issue is moderate in severity, the vehicle should not be driven due to the negative effect on the engines performance, such as acceleration, power, and throttle response.

In this article, we’ll explain what the P0299 OBD fault code means, its signs and causes, and how to fix it.

How Serious Is It?

A P0299 OBD fault code is rated as moderate in severity.

An issue such as under-boosting may not necessarily be dangerous for the engine, but it can cause issues with engine performance, such a throttle response, power, acceleration, etc.

However, if the turbine is broken, parts of the impeller could break off, enter the engine, and damage it.

Therefore, the vehicle should not be driven.

Always verify this diagnostic trouble code is real by using a high-quality OBD scanner, such as the ones below.

Possible Causes

  • A clogged air intake system.
  • Low pressure in the oil lubrication system, resulting in oil starvation.
  • A faulty injector control or boost pressure sensor
  • A defective wastegate or solenoid failure.
  • Blockages in the charger unit passages due to carbon deposits. This can be caused by using the wrong kind of oil or not servicing properly.
  • A sooty exhaust gas recirculation (EGR) valve resulting in carbon deposits obstructing the VNT mechanism.
  • Vacuum actuator failure.

Signs & Symptoms

A P0299 fault code usually results in drivability issues such as reduced engine power, throttle response, acceleration, etc.

How to Fix

Check for all possible causes of P0299 and attempt the most likely repairs, then clear the OBD system of fault codes, test drive the vehicle and scan again.

If the code reappears after you’ve attempted a fix, try the next repair option.

Common fixes for a P0299 fault code are to:

  1. Check for other or related OBD fault codes to see if the issue may be caused by something else.
  2. Examine the condition of hoses, pipes and vacuum lines linked to the supercharger or turbocharger.
  3. Tighten any loose hose clamps and replace damaged pipe components and seals to fix any leaks.
  4. Visually inspect the turbo or supercharger for cracks, damage, wear and tear, loose parts, etc.
  5. Check the sensors are working properly using an appropriate testing tool such as a multimeter.
  6. Ensure the wastegate and boost control solenoid is working correctly. You can test it manually with an air pump or vacuum tester.
  7. Check the EGR valve and system for damage and carbon deposits.
  8. You may need to clean the EGR valve and flush out the lubrication system.

Vehicles It’s Most Commonly Found On

The fault code P0299 can occur with any car but is most often found on the following cars.

  • Audi: A4, A1, A3
  • Ford: Transit, Mondeo, Fiesta
  • Mercedes: Sprinter, W204
  • Mazda: CX5, 6, 3
  • Opel: Astra, Corsa, Insignia
  • VW: Caddy, Polo, Transporter
  • Andy Lewin

    Andy Lewin is a senior mechanic, ASE qualified master technician, and an experienced automotive engineer. He's passionate about serving the automotive community with the highest-quality and trustworthy information on all things automotive. He loves to write about car repairs, maintenance, car modifications and tuning, faults, and much more.

Share this article
Available for Amazon Prime