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2020 E450 48V Battery Malfunction - EQ Boost System Warning

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Paul Z. · rep 0 · May 22, 4:13 AM · 1 replies · solved · Question

Vehicle: 2020 Mercedes-Benz E450 Sedan

Hi all,

I'm having a serious issue with my 2020 Mercedes-Benz E450 (W213) with the M256 engine and EQ Boost system. This morning, I got a '48V Battery Malfunction' warning on the dash, and the car wouldn't start. After a few tries, it eventually started, but the warning light stayed on, and the start/stop function isn't working.

I know these 48V mild hybrid systems are relatively new. Has anyone else experienced this with their E450 or other EQ Boost models? Is this a common failure point for the 48V battery or the integrated starter-generator (ISG)? I'm worried about being stranded. Any insights would be helpful!

Thanks, Sarah

✓ Accepted solution

ClearTheCode Admin

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

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ClearTheCode admin answer:

Issues with the 48V EQ Boost system on Mercedes-Benz models like your 2020 E450 are indeed a known concern, particularly in earlier production years of this technology. The system integrates the starter, alternator, and mild hybrid functions.

Here's what's typically involved:

  1. Understanding the System:

    • Causes: The 48V system powers various components and assists the engine. Malfunctions can stem from the 48V battery itself, the Integrated Starter-Generator (ISG), the DC/DC converter (which charges the 12V battery from the 48V system), or related wiring and control units.
    • Symptoms: Common symptoms include '48V Battery Malfunction' warnings, 'EQ Boost Malfunction,' vehicle not starting, loss of start/stop functionality, or reduced power.

  2. Common Failure Points:

    • 48V Battery: The lithium-ion 48V battery itself can fail, losing its ability to hold a charge or deliver sufficient current.
    • Integrated Starter-Generator (ISG): This unit, mounted between the engine and transmission, can develop internal faults.
    • DC/DC Converter: A failure here can prevent the 12V system from being properly charged, leading to a dead 12V battery even if the 48V system is operational.

  3. Diagnostic Steps (for a shop):

    • A Mercedes-Benz specific diagnostic tool (XENTRY/DAS) is essential. It will read fault codes from the relevant control units (e.g., N129/1 - 48V On-Board Electrical System Control Unit, or N82/2 - Integrated Starter Generator Control Unit).
    • Technicians will check voltage and current readings from the 48V battery and ISG, and perform functional tests of the system components.

When to See a Shop: Given the complexity and critical nature of the 48V system, you should have your E450 inspected by a Mercedes-Benz dealership or a specialized independent shop as soon as possible. This is not a DIY repair. Driving with a malfunctioning 48V system can lead to complete vehicle breakdown, and the high voltage components require specialized training and tools to handle safely. There have been extended warranty coverages or service campaigns for some of these issues, so inquire about that with your dealer.

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