Audi SQ8 EVAP Stalling Persists After Purge Fix

Had similar EVAP system failure symptoms on my 2018 Audi S6. The check engine light kept returning after purge valve replacement, along with rough idling. Initial diagnosis missed the root cause. The actual problem turned out to be a defective activated charcoal filter in the emission control system. The filter was completely saturated and unable to properly filter fuel vapors. This caused the fuel tank ventilation to malfunction, leading to irregular fuel system pressure. Key symptoms were: Stalling at idle, Recurring check engine warnings, Rough running after short-term fixes, Fuel cap pressure issues The repair required replacing the entire charcoal canister assembly since the component is not serviceable separately. This completely resolved the stalling issues and prevented further emission control system warnings. This is a known weak point in VAG EVAP systems, often misdiagnosed as just a bad purge valve. While not immediately dangerous for the engine, continued operation with a failed charcoal filter can impact fuel efficiency and eventually cause additional fuel system component wear. Consider requesting a smoke test of the complete EVAP system to verify the diagnosis before proceeding with repairs.

Thanks for the detailed reply about the charcoal filter issue. Having the same symptoms with my SQ8, the stalling and pressure sensor warnings were driving me crazy. Finally got it fixed last month when they found the faulty charcoal canister and air flow problems in the EVAP system. Just wondering how much the repair ended up costing you? Also curious if youve had any fuel tank ventilation issues since the fix? My system seems to be running fine now but would like to know what to watch out for.

Glad to hear you got it sorted with your SQ8. Since replacing the defective activated charcoal filter in my S6, the EVAP system has been working flawlessly. No more check engine lights or fuel tank ventilation problems for over 8 months now. The repair cost me 275 Euro for parts and labor. Pretty reasonable considering the comprehensive leak detection testing they had to do to confirm the issue. The price varies between shops, but replacing the charcoal filter is generally less expensive than repeatedly fixing other emission control components that arent the root cause. Nothing specific to watch out for since the fix, just maintain regular service intervals. If you notice any unusual fuel cap pressure or smell fuel vapors, those would be early warning signs of EVAP system issues. But with a new charcoal filter, the system should remain stable for many years of normal operation.

Finally got back from the shop today after dealing with my SQ8 issues. The repair bill came to 320 Euro, which included the new charcoal canister and system testing. More than I wanted to spend, but at least the car runs perfectly now. The stalling is completely gone and no more system failure warnings on the dash. The mechanic showed me the old charcoal filter, it was totally saturated and basically useless. Really explains why the previous purge valve replacement didnt solve anything. The pressure sensor readings are now stable and fuel efficiency seems better too. Really appreciate everyone who helped diagnose this. Saved me from throwing more money at temporary fixes. Will update if any fuel tank ventilation issues pop up, but so far its been running great for the past few weeks.