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2018 XC90 T6 Battery Draining Fast - Start/Stop Not Working

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Sarah K. · rep 0 · May 22, 5:13 AM · 1 replies · solved · Question

Vehicle: 2018 Volvo XC90 T6 Inscription

My 2018 Volvo XC90 T6 Inscription has been having issues with its battery. Over the last few weeks, the start/stop function has completely stopped working, and if the car sits for more than a day or two, the battery is completely dead. I've had to jump it multiple times.

I had the main battery tested at an auto parts store, and they said it was good, but maybe it's not holding a charge well. Could it be the auxiliary battery, or something else drawing power?

It's really frustrating, especially with winter coming. Any ideas on what to check first?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:13 AM

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ClearTheCode admin answer:

This sounds like a classic parasitic draw or a failing auxiliary battery, which is crucial for the start/stop system in your 2018 Volvo XC90 T6.

  1. Check the Auxiliary Battery: Even if your main battery tests good, the smaller auxiliary battery (often located in the trunk or under the hood near the main battery) is responsible for powering accessories during start/stop events. If it's weak or dead, the start/stop system will disable itself, and it can also contribute to overall battery drain. Have this battery tested specifically.
  2. Inspect for Parasitic Draw: A component staying active when the car is off can drain the battery. Common culprits include: infotainment modules, faulty door lock actuators, glove box lights, or even a malfunctioning alternator diode. This requires a multimeter to test current draw after the car has been asleep for about 30 minutes.
  3. Battery Management System (BMS): Volvo's sophisticated BMS can sometimes misinterpret battery health or fail to properly charge. A software update from a dealer might resolve communication issues within the system.
  4. Alternator Output: While less likely if the main battery tests 'good' after a jump, ensure your alternator is charging correctly (typically 13.5-14.5 volts) when the engine is running.

When to see a shop: If you're unable to locate a parasitic draw with a multimeter, or if replacing the auxiliary battery doesn't resolve the issue, it's best to visit a Volvo dealership or a specialized independent shop. They have diagnostic tools (VIDA) that can pinpoint specific module faults or software issues that might be causing the excessive drain.

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