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2018 XC90 T6 Start/Stop System Not Working - Battery or Sensor?

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David L. · rep 0 · May 22, 5:15 AM · 1 replies · solved · Question

Vehicle: 2018 Volvo XC90 T6 Momentum

Hey everyone,

I've got a 2018 Volvo XC90 T6 Momentum, and lately, the start/stop system hasn't been engaging at all. It used to work perfectly, but for the past few weeks, it just doesn't shut off the engine when I come to a stop, even when all conditions seem right (engine warm, not too hot/cold outside, A/C not blasting).

I haven't seen any warning lights on the dash, and the car otherwise drives fine. I'm wondering if this is a common issue with the battery starting to go bad, or if it could be a sensor problem? I've heard that the start/stop system is pretty sensitive to battery health.

Has anyone else experienced this with their XC90? Any tips on what I should check before taking it to the dealer? Thanks in advance!

✓ Accepted solution

ClearTheCode Admin

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

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ClearTheCode admin answer:

The Start/Stop system in your 2018 Volvo XC90 T6 is designed with multiple parameters that must be met for it to engage. When it stops working, it's often due to one of these conditions not being met, or less commonly, a component fault.

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

  1. Battery State of Charge (SoC) and Health: This is the most frequent culprit. The system requires a high state of charge (typically above 75-80%) and good battery health to operate. If your 12V battery is aging or not fully charged, the system will disable itself to ensure reliable engine starting. Have your battery tested for its health and charge level. A weak battery might not trigger a dashboard warning but will prevent Start/Stop.
  2. Ambient Temperature: Extreme temperatures (very cold or very hot) can prevent the system from engaging to maintain cabin comfort or engine efficiency.
  3. HVAC System Demand: If the climate control system is working hard to reach or maintain a set temperature, the engine may remain running.
  4. Steering Angle: If the steering wheel is turned significantly, the system may not engage.
  5. Brake Pedal Pressure: Insufficient brake pedal pressure at a stop can prevent engagement.
  6. Recent Engine Start: The system typically won't engage immediately after the engine has just been started.
  7. Engine Temperature: The engine needs to reach its optimal operating temperature.

When to See a Shop:

If you've ruled out the above conditions and the system still isn't working, it's time to visit a qualified Volvo service center. They can perform a diagnostic scan using VIDA (Volvo's diagnostic software) to check for specific fault codes. Potential codes might include:

  • BCM (Battery Control Module) or CEM (Central Electronic Module) related codes: Indicating issues with battery management or overall system communication.
  • ECM (Engine Control Module) codes: Pertaining to engine operation or sensor inputs.
  • Specific sensor codes: Such as those related to the battery current sensor, brake pedal position sensor, or crankshaft position sensor.

While a weak battery is the most common cause, a professional diagnosis will pinpoint any underlying electrical or sensor issues that might be preventing the system from functioning correctly.

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