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2018 XC90 T6: Start/Stop Not Working & '12V Battery Low' Message

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Mark S. · rep 0 · May 22, 5:15 AM · 1 replies · solved · Question

Vehicle: 2018 Volvo XC90 T6 Inscription

Hey everyone,

I've been having an intermittent issue with my 2018 Volvo XC90 T6 Inscription. For the past few weeks, the start/stop function has completely stopped working. I also occasionally get a '12V Battery Low' message on the dashboard, even after driving for an hour or more on the highway.

I'm wondering if this is a sign that my main 12V battery is on its way out, or if it could be related to the auxiliary battery that I know these cars have for the start/stop system. The car still starts fine, but the constant message and lack of start/stop are annoying.

Has anyone else experienced this with their XC90? What was the fix? Should I just replace the main battery, or is there something else I should check first?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:15 AM

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ClearTheCode admin answer:

The '12V Battery Low' message combined with a non-functional start/stop system in your 2018 Volvo XC90 T6 Inscription points to a common issue related to the vehicle's electrical system, specifically battery health or charging.

Here's a breakdown of potential causes and steps to take:

  1. Battery Degradation (Main or Auxiliary):

    • Main 12V Battery: Even if your car starts, the main battery might not be holding a sufficient charge to allow the start/stop system to engage. Modern vehicles require a high state of charge for these features. A battery's capacity naturally diminishes over time, especially after 4-6 years.
    • Auxiliary Battery: Many Volvo models, including your XC90, use a smaller auxiliary 12V battery specifically to power accessories during engine restarts by the start/stop system. If this battery is weak or failing, the start/stop function will be disabled, and it can sometimes trigger general 'battery low' warnings.

  2. Battery Management System (BMS) Issues: The BMS monitors the battery's state of charge, temperature, and overall health. A fault in the BMS could lead to incorrect readings or prevent proper charging, even if the battery itself is okay.

  3. Charging System Problems: While less common if the car is starting fine, a failing alternator or voltage regulator could be intermittently undercharging the battery, leading to the 'low voltage' message.

When to see a shop:

  1. Persistent Warnings: If the '12V Battery Low' message continues to appear despite long drives, it's time for a professional diagnosis.
  2. Starting Issues: If your car begins to crank slowly or struggles to start, address it immediately to avoid being stranded.
  3. Diagnostic Scan: A Volvo-specific diagnostic tool (like VIDA) can read specific fault codes related to the battery management system, auxiliary battery, or charging system that generic OBD-II scanners might miss. Look for codes like P0562 (System Voltage Low) or manufacturer-specific codes related to battery control modules.

Recommendations:

  • Battery Test: Have both your main 12V battery and the auxiliary battery tested by a reputable shop. They can perform a load test to determine their true health. Often, replacing the auxiliary battery resolves the start/stop issue and related warnings.
  • Check Connections: Ensure battery terminals are clean and tight on both batteries.
  • Professional Diagnosis: A Volvo specialist can accurately pinpoint whether it's the main battery, auxiliary battery, BMS, or another electrical component causing the problem. They can also check for software updates related to battery management that might resolve the issue.
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