Q5 Power Loss & ECU Issues, Expert Repair Help Needed

I experienced similar engine performance issues on my 2011 A4 2.0T. The symptoms match what you describe, reduced power and error codes in the engine control system. The root cause was a defective main relay in the computer module, which caused intermittent electrical supply to the ECU. This is a critical component that requires proper diagnosis with specialized car diagnostics equipment. A faulty main relay can cause various issues including: Unusual power loss while driving, Engine stalling, Check engine light activation, Inconsistent starting, Erratic idle behavior The repair involved replacing the main relay and running a full diagnostic scan to ensure all systems were communicating properly. This was not a simple fix-it-yourself job due to the complexity of automotive electronics involved. The issue took about 4 hours to properly diagnose and repair. Given the symptoms and mileage on your Q5, I suggest having the main relay tested by a specialist who focuses on engine control systems. Look specifically for shops that specialize in VAG automotive electronics, as they will have the proper diagnostic tools and experience with these systems. When working with engine performance issues tied to electrical systems, proper diagnosis is crucial before replacing parts.

Thanks for sharing your experience with the A4 relay issue. It does sound very similar to what was happening with my Q5. A while back, I also faced weird electrical glitches and reduced power output. After a system reset didn't help, I had to get the ECU problems checked out by a specialist. Did you happen to keep track of the repair costs? Also, has everything been running smoothly since the main relay replacement? Just wondering if any other engine performance issues came up later.

Since getting the ECU repair done on my A4, everything has been running perfectly with no additional engine control issues. The total cost came to 120 Euro for replacing the defective main relay, which included diagnostic testing to confirm the fix worked properly. The vehicle electronics are now functioning as they should, with no more power loss or error codes appearing. Looking back, having a specialist repair the automotive electronics was definitely worth the investment. The engine performs consistently now and starts reliably every time. I track all repairs meticulously and can confirm there have been zero ECU problems or electrical system issues in the 8 months since the repair. The original symptoms completely disappeared after the faulty main relay was replaced. For anyone dealing with similar engine control unit issues, getting an accurate diagnosis from someone experienced with these specific automotive electronics is crucial for a proper fix.

I finally decided to take my Q5 to a specialist automotive electronics shop after reading about your experience. The technician ran complete car diagnostics and found that my main relay was indeed failing, just like in your case. The repair took about 3 hours total. The computer module needed a full system reset after the new relay was installed. Including parts and labor, I paid 180 Euro for the complete ECU repair job. Its been 2 weeks now and the engine performance is back to normal. No more error codes or power reduction warnings. The shop did a great job explaining the vehicle electronics issues and showed me the worn components they replaced. Much better experience than my previous mechanic. Thanks for pointing me in the right direction with the relay suggestion. Sometimes finding the right specialist makes all the difference when dealing with complex automotive electronics repairs.