Subaru R2 Power Surge Chaos: Voltage Mystery Symptoms

I had a very similar issue with my 2005 Subaru R1 last winter. Having some experience with electrical issues, I first suspected a simple car battery problem, but it turned out to be more complex. The symptoms matched yours exactly, unusual electrical failures, voltage regulator warnings, and power surge indicators across multiple systems. The workshop found that the battery was heavily discharged due to a faulty voltage regulator that was causing inconsistent charging patterns. The repair involved: Complete electrical system diagnosis, Replacement of the voltage regulator, New battery installation, System reset and monitoring Total cost was 290€, but it solved all the electrical issues permanently. No more unusual system failures or starting problems since then. Before suggesting specific solutions, could you share: How old is your current battery? Do you see any corrosion on battery terminals? Are the electrical issues more frequent when its cold or after the engine warms up? What voltage readings are you getting at idle? This information would help determine if your issue matches what I experienced or if there might be other factors at play.

Mileage: 153235 KM Last service: 3 months ago Thanks for the detailed response. The car ECU logs show similar voltage spikes. My current battery is just 4 months old, and terminals are clean. The power surge issues happen more frequently when the engine is warm, especially during longer drives. Voltage readings fluctuate between 12.8V and 15.2V at idle, which seems too high. The alternator warning typically appears after 20 minutes of driving. Based on your experience, this really sounds like a failing voltage regulator rather than the alternator itself. Will have the shop check these specific components. Good to know the fix was permanent in your case.

Thanks for the voltage readings, they definitely point toward the voltage regulator being the culprit, just like in my case. The fluctuation pattern between 12.8V and 15.2V is a textbook sign of electrical issues caused by a faulty regulator. The alternator failure warnings appearing after 20 minutes match exactly what I experienced. In my case, the overvoltage would trigger multiple system warnings as the drive continued. These high voltage spikes can eventually damage other electrical components if left unchecked. One difference I notice, my issues occurred more in cold conditions, while yours worsen with a warm engine. This suggests your voltage regulator might be heat-sensitive, which is actually more common in the R2 model compared to my R1. Since your symptoms are nearly identical and the power surge pattern matches, I strongly recommend having the voltage regulator replaced first before considering a full alternator replacement. The repair should be cheaper than my 290€ job since you already have a new battery. A tip from my experience: have them check the circuit protection module while they are at it. These components often work together, and testing both can prevent future electrical issues.

Really appreciate your insights about the voltage regulator. The heat sensitivity explanation makes sense given my symptoms, and those voltage readings definitely confirm we are dealing with similar issues. Just booked the car in for next week. Asked them specifically to check both the voltage regulator and circuit protection module based on your experience. The service advisor confirmed these components commonly fail together on these models and cause power surge problems. My readings being identical to yours gives me confidence we have identified the root cause. Good to know the repair was permanent in your case, hoping for similar results. Will insist on a full electrical system diagnosis first, just as you suggested. The shop quoted 250€ for the complete job, which seems reasonable considering your repair costs. At least I can avoid replacing the alternator if the voltage regulator turns out to be the main culprit. Thanks again for the detailed help in narrowing down these electrical issues. Having a clear direction for the repair is exactly what I needed.