Seat Formentor Diesel Engine Issue

That's a tricky one. Reduced power and higher fuel consumption often point towards fueling or air intake issues. Could be a clogged air filter, but with those symptoms and the check engine light, I'd suspect something more serious. Have you checked the spark plug condition? I would suggest you run some tests. It's like having a leaky faucet; it can be a simple washer or a major plumbing problem.

I appreciate your response. I have not checked the spark plug, as this is a diesel engine. Could the issue possibly be related to the head gasket or the turbocharger system, given the mileage? And if it was the spark plug, would the error disappear once the faulty plug is exchanged?

Apologies, I missed the diesel part. Yes, head gasket or turbocharger issues are definitely possibilities given the symptoms and mileage. However, the ECU is so sensitive these days it could be just a sensor failure causing the chain reaction of symptoms. It's best to get it properly diagnosed at a workshop. They can check the actual cylinder pressures, error codes and sensor data to pinpoint the root cause.

I appreciate your input. Turns out the cylinder pressure fluctuation was a consequential error. After a thorough diagnostic check, the issue stemmed from a faulty sensor causing misreporting. No actual engine damage, so thankfully the repair was just a sensor replacement. Cost me nothing under warranty.