How does Oil or Fuel get into ECU's ? Oil or fuel can enter an Engine Control Unit (ECU) through a few potential routes, unfortunately it is a fairly common occurrence. Here’s how it can happen: If the wiring harness connected to the ECU becomes damaged or if there is a breach in the insulation, oil or fuel can seep through the wiring. This can occur if there is a leak in the engine or fuel system, allowing fluids to travel along the wiring into the ECU. Faulty Wiring Harness: If the wiring harn