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2020 Mini Cooper S Start-Stop Not Engaging - Battery or Sensor Issue?

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Angela R. · rep 0 · May 22, 6:58 AM · 1 replies · solved · Question

Vehicle: 2020 Mini Cooper S

Hey everyone,

I've got a 2020 Mini Cooper S, and lately, the auto start-stop system hasn't been engaging at all. It used to work perfectly, but now even on longer drives, it just stays off. I don't have any warning lights on the dash, but it's definitely noticeable.

Could this be a sign of a dying battery, or is there a specific sensor that might be acting up? I'm in the US, and it's been pretty mild weather here, so I don't think it's extreme temperatures preventing it. I've checked the button on the dash, and it's definitely enabled.

Any ideas on what I should check first before taking it to the dealer? Thanks for any help!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 6:58 AM

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ClearTheCode admin answer:

The auto start-stop system in your 2020 Mini Cooper S is designed to optimize fuel efficiency, but it relies on several conditions being met to engage. When it stops working, the battery is often the primary suspect, but other factors can also play a role.

Here's a breakdown of common causes and what to check:

  1. Battery Health:

    • Cause: The most common reason for start-stop not engaging is an insufficient battery charge or a weakening battery. The system requires a robust battery to ensure a reliable restart. If your battery's state of charge (SOC) or state of health (SOH) is below a certain threshold, the system will disable itself to prevent potential starting issues.
    • Action: Check your battery's voltage. A healthy battery should read around 12.6V when the engine is off. If it's consistently lower, or if the battery is several years old, it might be time for a replacement. Many auto parts stores offer free battery testing.

  2. Intelligent Battery Sensor (IBS):

    • Cause: The IBS monitors the battery's condition, temperature, and current flow. A faulty IBS can send incorrect data to the engine control unit (ECU), leading to the start-stop system being disabled. While less common, it's a possibility.
    • Diagnostics: A diagnostic scan tool might reveal codes related to the charging system or IBS, such as P0562 (System Voltage Low) or manufacturer-specific codes indicating an IBS malfunction.

  3. Other System Conditions:

    • Cause: The start-stop system will not engage if various other conditions are not met. These include:
      • Engine not at optimal operating temperature.
      • Ambient temperature too high or too low.
      • Climate control (AC/heater) demand is high.
      • Steering wheel turned significantly.
      • Vehicle not driven long enough since last start.
      • Driver's seatbelt not fastened.
      • Brake vacuum pressure is low.
      • Battery temperature is outside optimal range.

When to See a Shop:

  • If your battery tests good, but the start-stop system still doesn't work, and you've ruled out all other common conditions.
  • If you notice any warning lights on your dashboard, especially those related to the charging system or engine.
  • If a diagnostic scan reveals specific fault codes (DTCs) that point to sensor failures or control module issues.

A qualified Mini technician can perform a comprehensive diagnostic scan and pinpoint the exact cause of the malfunction, whether it's a failing battery, an IBS issue, or another system component.

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