The largest online repair guide library for every car

About us
Contact support
FAQ
Sign up
Sign in

Loss of Power and Whistling Noise on 2017 GLC300 - P0299 Code

0

Nicole W. · rep 0 · May 22, 4:13 AM · 1 replies · solved · Question

Vehicle: 2017 Mercedes-Benz GLC300

Hello everyone,

I'm having a frustrating issue with my 2017 Mercedes-Benz GLC300 (X253). For the past few weeks, I've noticed a significant loss of power, especially when accelerating onto the highway. It feels sluggish and just doesn't have the same punch it used to.

To make things worse, there's a distinct whistling or sometimes even a hissing sound coming from the engine bay when I accelerate. The check engine light came on, and when I scanned it, I got a P0299 code, which I believe means 'Turbocharger/Supercharger Underboost'.

Has anyone dealt with this on their GLC300? What's the most common culprit for this code and symptoms? Is it a simple fix or something major?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:13 AM

0

ClearTheCode admin answer:

The P0299 code, combined with a whistling/hissing noise and loss of power on your 2017 GLC300, strongly points to an issue with the turbocharger system, specifically an underboost condition.

Here's a breakdown of the likely causes and what to do:

  1. Understanding P0299 (Underboost): This code means the engine's actual boost pressure is lower than what the engine control unit (ECU) expects. This directly translates to reduced engine power.

  2. Common Causes for Underboost and Whistling/Hissing:

    • Boost Leaks: This is the most common cause. A crack or loose connection in the charge air pipes (intercooler hoses) or the intercooler itself can allow boost pressure to escape, creating a whistling or hissing sound.
    • Wastegate Actuator/Valve Issues: The wastegate controls the exhaust gas flow to the turbo. If it's stuck open or its actuator is faulty, the turbo won't build sufficient boost.
    • Turbocharger Failure: While less common than leaks, the turbocharger itself could be failing (e.g., worn bearings, damaged impeller), leading to inefficient boost production and potentially noise.
    • Diverter Valve/Bypass Valve: A faulty diverter valve can leak boost pressure.

  3. When to See a Shop:

    • Promptly: Driving with an underboost condition can lead to further issues and reduced fuel economy. It's best to address it as soon as possible.
    • Diagnosis: A qualified technician will perform a smoke test to identify boost leaks, inspect the turbocharger and its components, and check sensor readings (like MAP sensor) to pinpoint the exact cause.
    • Repair: The repair could range from replacing a simple hose clamp to replacing a charge pipe, a wastegate actuator, or, in more severe cases, the turbocharger itself.
Menu

Help & account