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2020 E450 Transmission Limp Mode & Hard Shifts - P0730 Code

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Paul Z. · rep 0 · May 22, 4:11 AM · 1 replies · solved · Question

Vehicle: 2020 Mercedes-Benz E450

Hi all,

I'm having some serious transmission issues with my 2020 Mercedes-Benz E450 (W213, 3.0L V6). A few days ago, it suddenly went into limp mode, and the Check Engine Light came on. I pulled the code, and it's P0730, which points to an incorrect gear ratio.

Before this, I noticed some occasional hard shifts, especially from 2nd to 3rd gear, and sometimes a slight hesitation when accelerating from a stop. Now, in limp mode, it's stuck in a higher gear, and acceleration is very sluggish. I've tried restarting the car, but the issue persists.

Has anyone else experienced this with their E450 or a similar Mercedes model with the 9G-Tronic transmission? What was the fix? I'm really hoping it's not a full transmission replacement, as the car isn't that old.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:11 AM

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ClearTheCode admin answer:

A P0730 code (Incorrect Gear Ratio) on your 2020 Mercedes-Benz E450, especially when accompanied by limp mode and hard shifts, indicates a significant issue within the 9G-Tronic (9G-TRONIC PLUS) automatic transmission. This code means the transmission control module (TCM) detects that the actual gear ratio does not match the commanded gear ratio.

Here's a breakdown of common causes and diagnostic steps:

  1. Low or Contaminated Transmission Fluid:

    • Diagnosis: While Mercedes transmissions are often considered 'sealed for life,' fluid levels can drop due to leaks, or the fluid can degrade over time. Low fluid can cause pressure issues, leading to incorrect gear engagement. Contaminated fluid can damage internal components.
    • Causes: Leaks from seals or pan, overdue fluid service.

  2. Transmission Valve Body Issues:

    • Diagnosis: The valve body is critical for directing hydraulic pressure to engage gears. Solenoids within the valve body can stick or fail, preventing proper gear changes. This is a very common failure point in modern automatic transmissions.
    • Causes: Electrical faults in solenoids, mechanical sticking of valves due to debris or wear.

  3. Internal Transmission Mechanical Failure:

    • Diagnosis: This is the most severe scenario. Worn clutch packs, damaged planetary gears, or other internal hard part failures can lead to incorrect gear ratios. This often presents with grinding noises or complete loss of drive.
    • Causes: Excessive wear, lack of lubrication, manufacturing defect.

  4. Transmission Control Module (TCM) Fault:

    • Diagnosis: Less common, but the TCM itself could be faulty, sending incorrect signals or misinterpreting sensor data. A specialized diagnostic tool can check for TCM communication errors.
    • Causes: Internal electronic failure, software glitches.

When to see a shop:

Given that your E450 is in limp mode and displaying a P0730 code, it is crucial to have it inspected by a Mercedes-Benz dealership or a specialized independent transmission shop immediately. Driving the vehicle in this state can cause further, more extensive damage to the transmission. They will use specific Mercedes diagnostic software (XENTRY/DAS) to read detailed fault codes, check live data from the transmission sensors, and perform guided tests to accurately pinpoint the internal issue. A transmission fluid and filter service might be recommended, but often, valve body replacement or internal repairs are necessary for this type of fault.

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