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2017 XC90 T6 Auxiliary Battery Drain & Start-Stop Not Working

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Jennifer H. · rep 0 · May 22, 5:18 AM · 1 replies · solved · Question

Vehicle: 2017 Volvo XC90 T6 Momentum

Hey everyone,

I've got a 2017 Volvo XC90 T6 Momentum, and I'm having persistent issues with the start-stop system not engaging. More concerning, I've had a couple of instances where the main battery drained completely after the car sat for a few days.

I suspect it might be related to the auxiliary battery, which I know is common on these early SPA platform cars. The dealer quoted me a pretty high price for replacement. Has anyone dealt with this? Is it something I can tackle myself, or is it best left to the pros?

Also, are there any specific diagnostic steps or codes I should look for? I'm trying to avoid unnecessary costs.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:18 AM

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ClearTheCode admin answer:

  1. Diagnose the Issue: The symptoms you describe, especially the start-stop not working and main battery drain, strongly point to a failing auxiliary battery. The auxiliary battery powers the start-stop system and other low-voltage electronics. When it fails, the main battery can be overtaxed or experience parasitic drain.

  2. Check for OBD Codes: While a failing auxiliary battery might not always throw a specific OBD-II code, a general system voltage low code like P0562 (System Voltage Low) or P0560 (System Voltage Malfunction) could appear if the main battery is also struggling. A good shop will also check for specific Volvo diagnostic trouble codes (DTCs) related to the battery management system.

  3. Causes: The auxiliary battery in many 2016-2018 Volvo XC90s has a known tendency to fail prematurely. This is often due to its design life or environmental factors. It's a common wear item.

  4. DIY vs. Professional: Replacing the auxiliary battery can be a DIY task for someone with moderate mechanical skills. It's typically located under the hood or in the trunk, depending on the specific model year and configuration. However, proper disconnection and reconnection procedures are crucial to avoid electrical issues. If you're not comfortable working with automotive electrical systems, especially given the complexity of modern Volvos, it's best to have a professional handle it. They can also properly register the new battery with the car's system if required, which ensures optimal charging and longevity.

  5. When to See a Shop: If you're unsure about the diagnosis, lack the tools, or are uncomfortable with electrical work, take your XC90 to a reputable Volvo specialist or dealership. They can perform a comprehensive battery test (main and auxiliary), check for parasitic drains, and ensure the correct battery is installed and registered. Ignoring a failing auxiliary battery can lead to more significant electrical problems down the line.

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