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2021 A6 MHEV Start/Stop Not Working Consistently

0

Brittany E. · rep 0 · May 22, 4:25 AM · 1 replies · solved · Question

Vehicle: 2021 Audi A6 3.0T Premium

Hello everyone,

I have a 2021 Audi A6 3.0T Premium with the mild-hybrid system, and I've noticed that the start/stop function isn't working consistently. Sometimes it works perfectly, shutting off the engine at lights and restarting smoothly. Other times, even when all the conditions seem right (engine warm, battery charged, seatbelt on, etc.), it just doesn't engage.

There are no warning lights on the dash, and the car drives perfectly otherwise. It's just an annoyance that the MHEV system isn't performing as expected. Is this a common issue with these mild-hybrid Audis? Could it be related to the 48V battery, or something else entirely?

Any advice would be appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:25 AM

0

ClearTheCode admin answer:

The inconsistent operation of the start/stop system in your 2021 Audi A6 3.0T with the mild-hybrid (MHEV) system is a common observation among owners. While it can be frustrating, it's often not indicative of a major fault, but rather the system's sophisticated logic deciding not to engage for various reasons.

Here are the most common reasons why the MHEV start/stop system might not activate, even if you think all conditions are met:

  1. Battery State of Charge (12V and 48V): Both the conventional 12V battery and the 48V MHEV battery need to be sufficiently charged. If either is below a certain threshold, the system will disable start/stop to prioritize charging. Short trips, cold weather, or an aging 12V battery can impact this.
  2. Ambient Temperature: The system has temperature limits. If it's too cold or too hot outside, the start/stop function may be temporarily disabled to ensure optimal engine and HVAC performance.
  3. HVAC Demand: If the climate control system is working hard to reach or maintain a set temperature (e.g., rapidly cooling a hot cabin or defrosting), the engine may stay on to power the compressor or heater.
  4. Steering Angle/Brake Pressure: If the steering wheel is turned significantly, or if brake pedal pressure is insufficient, the system may not engage. It needs to detect a complete stop and a stable vehicle position.
  5. Engine Warm-up/Cool-down: The engine needs to reach optimal operating temperature. Also, after a hard drive, the engine might stay on to cool down the turbocharger.
  6. System Diagnostics: If the car's internal diagnostics detect any minor fault or an ongoing system check, the start/stop might be temporarily disabled.

When to see a shop: If the inconsistency becomes very frequent, or if you notice any other electrical issues, it's worth having an Audi specialist perform a diagnostic scan. They can check the health of both your 12V and 48V batteries, look for any stored fault codes (even if no warning light is on), and check for any available software updates for the MHEV system. Sometimes, a simple battery test on the 12V battery can reveal it's nearing the end of its life, which can impact MHEV functionality.

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