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Rough Idle & Check Engine Light on my 2018 C300 - Camshaft Issue?

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Laura J. · rep 0 · May 22, 4:21 AM · 1 replies · solved · Question

Vehicle: 2018 Mercedes-Benz C300

Hey everyone,

I'm experiencing some concerning issues with my 2018 Mercedes-Benz C300 (W205 chassis, M274 engine). Lately, the car has developed a really rough idle, especially when cold, and sometimes feels like it's struggling to accelerate smoothly. The check engine light also came on a few days ago and hasn't gone off.

I've heard some chatter about camshaft adjuster or timing chain problems with these M274 engines around this model year. Has anyone else with a 2016-2019 C300 or similar model experienced this? What was the diagnosis and the fix?

I'm trying to get a sense of what I might be looking at before I take it to the dealership. Any advice or shared experiences would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:21 AM

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ClearTheCode admin answer:

It sounds like you're describing a common issue that can affect the M274 engine in your 2018 Mercedes-Benz C300. The symptoms of rough idle, reduced power, and a check engine light often point towards problems with the camshaft timing system.

Here's what you should consider:

  1. OBD-II Code Retrieval: The first step is to get the diagnostic trouble codes (DTCs) read. Common codes associated with camshaft timing issues include:

    • P0016: Crankshaft Position - Camshaft Position Correlation (Bank 1 Sensor A)
    • P0017: Crankshaft Position - Camshaft Position Correlation (Bank 1 Sensor B)
    • P0012: "A" Camshaft Position - Timing Over-Retarded (Bank 1)
    • P0015: "B" Camshaft Position - Timing Over-Retarded (Bank 1) These codes indicate a discrepancy between the crankshaft and camshaft positions, suggesting a timing problem.

  2. Potential Causes:

    • Camshaft Adjusters (Sprockets): These can fail internally, leading to incorrect valve timing. This is a very common failure point for the M274 engine. The internal locking pins can break, causing the timing to be out of sync.
    • Camshaft Position Sensors: While less common than adjuster failure, faulty sensors can send incorrect signals to the engine control unit (ECU), leading to similar symptoms.
    • Timing Chain Stretch: Over time, timing chains can stretch, causing the timing to drift. This is generally more prevalent in higher mileage vehicles but can occur.

  3. When to See a Shop: You should take your C300 to a qualified Mercedes-Benz specialist or dealership as soon as possible. Driving with incorrect valve timing can lead to further, more severe engine damage over time. A professional will be able to perform a thorough diagnosis, which may include:

    • Reading live data from the camshaft position sensors.
    • Inspecting the camshaft adjusters for play or damage.
    • Checking for any relevant Technical Service Bulletins (TSBs) or recalls related to the M274 engine's timing components. Mercedes-Benz has issued updated parts for these adjusters.

Addressing this issue promptly can prevent more costly repairs down the line.

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