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Squealing noise from engine bay on 2021 CLA250 - Serpentine belt?

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Eric V. · rep 0 · May 22, 4:19 AM · 1 replies · solved · Question

Vehicle: 2021 Mercedes-Benz CLA250

Hi everyone,

I've got a 2021 Mercedes-Benz CLA250 (C118 chassis) with about 30,000 miles on it. For the past few weeks, I've been hearing a distinct squealing noise coming from the engine bay, especially when I first start the car in the morning or after it's been sitting for a while. It usually goes away after a few minutes of driving.

Could this be the serpentine belt, or maybe one of the pulleys? The car runs fine otherwise, and there are no warning lights on the dash. Is this something I should be concerned about, and is it a difficult DIY fix?

Thanks for your input!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:19 AM

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Hello Jessica,

The squealing noise you're hearing from your 2021 CLA250, particularly on cold starts and disappearing after a few minutes, is a very common indicator of an issue with the serpentine belt or one of its associated pulleys. At 30,000 miles, it's a bit early for a belt to be completely worn out, but issues can arise.

Common Causes of Squealing:

  • Worn or Glazed Serpentine Belt: The rubber can harden, crack, or become glazed, losing its grip on the pulleys.
  • Misaligned or Worn Pulleys: Pulleys (tensioner, idler, alternator, AC compressor, power steering pump) can develop worn bearings, causing them to wobble or create friction.
  • Automatic Belt Tensioner Failure: The tensioner spring can weaken, leading to insufficient belt tension.
  • Contamination: Oil, coolant, or other fluids on the belt can cause it to slip and squeal.

Diagnosis and Repair Steps:

  1. Visual Inspection: With the engine off and cold, inspect the serpentine belt for cracks, fraying, glazing, or any signs of fluid contamination. Also, check the pulleys for excessive wobble or play.
  2. Listen Carefully: Use a mechanic's stethoscope (or a long screwdriver to your ear, carefully) to pinpoint the source of the noise while the engine is running and squealing. This can help identify a specific failing pulley.
  3. Belt Replacement: If the belt is worn, replacing it is a relatively straightforward DIY task on many Mercedes-Benz models, including the CLA250. You'll need to release the tensioner, remove the old belt, and route the new one correctly. Always use a high-quality OEM or equivalent belt.
  4. Pulley/Tensioner Replacement: If a pulley or the tensioner is the culprit, these can also be replaced. This might require specific tools for removal and installation.

When to See a Shop:

  • If you're uncomfortable working around a running engine or with the belt routing.
  • If the noise persists after replacing the belt, indicating a deeper issue with a component like the alternator or AC compressor.
  • If you notice any fluid leaks that might be contaminating the belt.
  • There are no direct OBD-II codes for a squealing belt or bad pulley, as these are mechanical issues. However, if a component driven by the belt (like the alternator) fails, it could trigger a battery warning light and related charging system codes (e.g., P0562 - System Voltage Low).

Addressing this issue promptly is important, as a failing belt can lead to loss of power steering, AC, and charging, potentially leaving you stranded.

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