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2021 GLC300 - Start/Stop Not Working, Multiple Warning Lights

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Brittany E. · rep 0 · May 22, 4:12 AM · 1 replies · solved · Question

Vehicle: 2021 Mercedes-Benz GLC300

Hey everyone,

I'm having a weird electrical issue with my 2021 Mercedes-Benz GLC300 (X253). For the past week, the ECO Start/Stop function has completely stopped working. On top of that, I've started getting intermittent warning lights for ABS, ESP, and sometimes even the Pre-Safe system.

The car starts fine, and drives okay, but these warnings pop up randomly, especially after a cold start or short drive. I haven't scanned for codes yet, but I'm wondering if this is a common issue with the auxiliary battery or maybe the main battery starting to fail? Or could it be something else entirely?

Any thoughts or similar experiences with your GLCs would be really helpful!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:12 AM

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ClearTheCode admin answer:

The combination of ECO Start/Stop not working and multiple, seemingly unrelated warning lights (ABS, ESP, Pre-Safe) on your 2021 Mercedes-Benz GLC300 is a strong indicator of a voltage supply issue. Modern Mercedes vehicles are highly sensitive to battery voltage and can exhibit a wide range of electronic malfunctions when the battery is weak or failing.

Common Causes for These Symptoms:

  1. Main Battery Degradation: The primary 12V battery is the most common culprit. As batteries age, their capacity to hold a charge and deliver sufficient cranking amps diminishes, leading to low voltage conditions that affect various electronic control units (ECUs). The ECO Start/Stop function is often the first feature to disable itself when battery voltage is suboptimal.
  2. Auxiliary Battery Failure: Many Mercedes models, including the GLC, use a smaller auxiliary battery (often a capacitor or small lead-acid battery) to support certain functions, particularly the Start/Stop system and gear selector. A failing auxiliary battery can directly cause the Start/Stop system to cease functioning and can sometimes contribute to other electrical glitches.
  3. Alternator/Charging System Issue: If the alternator isn't properly charging the battery, the system voltage will drop, leading to similar symptoms.
  4. Loose or Corroded Battery Terminals: Poor connections at the battery terminals can restrict current flow and cause voltage drops.
  5. Parasitic Drain: Something in the vehicle could be drawing power when the car is off, slowly draining the battery.

Troubleshooting Steps:

  1. Battery Test: Have both your main 12V battery and auxiliary battery (if applicable) professionally tested for their state of charge and health. Many auto parts stores offer this service for free.
  2. Check Terminals: Ensure both battery terminals are clean, tight, and free of corrosion.
  3. Scan for Codes: Use an OBD-II scanner to retrieve any stored fault codes. Even if the lights are intermittent, codes are likely stored in the ABS, ESP, or other modules.

When to See a Shop:

While a battery issue is highly probable, it's best to have a Mercedes-Benz specialist or dealership perform a comprehensive diagnostic. They can:

  • Accurately test both the main and auxiliary batteries.
  • Check the alternator's output and the entire charging system.
  • Access specific fault codes from all relevant control modules (ABS, ESP, Engine, Transmission, etc.) using Mercedes-specific diagnostic tools (XENTRY/DAS). This will help differentiate between a simple battery replacement and a more complex electrical issue. Addressing this promptly will prevent potential safety system malfunctions and ensure reliable vehicle operation.
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