Audi Q8 Start-Stop System Fails During Active Driving

Having some experience with car repairs, I faced a similar issue with my Audi Q7 2020. The engine stalling problem was quite similar to what you describe, especially with the automatic restart system acting unpredictably. After multiple occurrences of engine stalling, I took it to a workshop. The diagnostic revealed a heavily discharged battery that was causing the start-stop system to malfunction. The battery issue was affecting multiple systems, including the Eco mode features. The complete fix included: Battery testing and replacement, System reset, Start-stop system recalibration Total cost was 290 Euro for parts and labor. Since the repair, the automatic restart system has worked flawlessly. To provide more specific advice for your case, could you share: Current battery age, Warning messages displayed, Whether the issue occurs more frequently during cold starts, Mileage of your vehicle This information would help determine if your Q8 is experiencing the same battery issue or if there might be other factors involved.

Just had my service last week at 169458 KM. The issue persists even after they checked the battery, which tested fine during diagnostics. The warning message only shows start-stop system fault and the engine stalling happens around 3-4 times per hour of driving. The start-stop system worked perfectly until last month. Even in heavy traffic the automatic restart was smooth. Now the hybrid vehicle features are basically unusable. Considering taking it to another workshop for a second opinion since the first check didnt resolve anything. The idle stop feature is completely unpredictable now, making daily driving quite stressful.

Since we both have similar Audi models and battery issues seemed the obvious culprit initially, I understand your frustration when the battery test came back normal. After my previous experience, I can suggest checking a few other components that could cause these symptoms. In my case, while the battery was the main issue, the mechanic also found that the voltage regulator and alternator were contributing to the start-stop system malfunction. The car battery might test fine but still not receive proper charging during operation. When my start-stop system acted unpredictably like yours, these components were checked: Alternator output, Voltage regulator function, Start-stop sensor connections, Engine control module The complete diagnostic revealed corroded connections at the voltage regulator, causing intermittent power supply issues affecting the Eco mode and start-stop functions. The repair involved: Cleaning and replacing corroded connections, Updating engine control software, Testing all start-stop sensors Total repair cost was 380 Euro, significantly less than a potential hybrid system repair. Since then, the automatic restart works perfectly again. Given your mileage and symptoms, I would specifically request checking these components at the second workshop.

Thanks for sharing those additional repair suggestions. I went ahead and booked another workshop appointment next week. The symptoms you described with the voltage regulator match my situation perfectly, especially the unpredictable engine start behavior even when the car battery tests fine. My start-stop system issues began right after some heavy rain, which could explain potential corrosion problems affecting the connections. The idle stop feature has been completely unreliable since then. Looking at the repair costs you mentioned, 380 Euro seems reasonable if it fixes these constant automatic restart failures. Will update once the second workshop checks the voltage regulator and other components you suggested. Really hoping they can resolve this since the engine stalling is making the car almost unusable for daily driving. The first mechanic seemed too focused on just the battery, so having these additional areas to investigate is helpful.