Skoda Kodiaq Diesel Engine Trouble

Reduced engine power and higher fuel consumption with a check engine light? That does sound like an emission control issue. Is the engine running rough, or is it mostly just a lack of power? Have you checked for any obvious exhaust leaks? A visual inspection might reveal something before you start sensor replacement.

The engine runs smoothly, just feels like it's being held back. I haven't checked for leaks, where exactly should I be looking in the exhaust system?

Smooth running but lacking power does point away from major engine problems. A small exhaust leak near the heat sensor could definitely cause it to read incorrectly and throw the system into a reduced power mode for emission control reasons. Locating exhaust leaks can be tricky without proper equipment. It might be best to take it to a workshop. They can do a smoke test to pinpoint any leaks and confirm the sensor's functionality before recommending sensor replacement. It is likely an exhaust component issue.

It was the exhaust temperature sensor. The workshop found a small leak in the exhaust system, which probably caused the sensor to fail. Sensor replacement and sealing the leak cost 265€. Thanks for the help!