Seat Formentor Diesel Reduced Engine Power

Sounds like a potential ECU issue. Have you checked the wiring harness for damage or corrosion? What error codes are stored? That's crucial for diagnosing electronics problems like this. A defective main relay could cause the computer module to malfunction, leading to reduced engine performance.

Good point about the error codes; should have included that. It's showing code P0606, which points to the engine control unit itself. Thoughts? Does this still sound like the main relay?

P0606 definitely points towards an internal ECU fault. While a faulty relay could contribute, the error code suggests the ECU itself is compromised. Given the age and mileage, it's plausible. I would advise having a workshop confirm the diagnosis, as ECU issues can be complex. Time to get it professionally checked.

It was a defective main relay, like I thought. The ECU repair was 120€. Thanks for the help.