Ever wonder what actually goes wrong when a vehicle sits unused for years? This is the PCM (Powertrain Control Module) — basically the brain of your vehicle. When a car sits for 4 years, moisture and corrosion don’t just show up on the surface. They creep into wiring, power supplies, and communication circuits. In this case, corrosion caused shorts and battery drain, damaged the original PCM, and forced a replacement. Now the job isn’t just installing parts — it’s reprogramming the system so the