Peugeot 4008 exhaust temperature sensor fault

The symptoms you describe, coupled with the exhaust temperature sensor fault code, do point towards a potential issue within the exhaust system. It is plausible that a leak could be influencing the sensor's readings, leading to temperature fluctuation and consequently, the engine management system reducing power to protect the catalytic converter. Have you visually inspected the exhaust system for any signs of damage or leaks?

I took a quick look under the car, but didn't spot anything obvious like holes or cracks. Is there a specific area of the exhaust system that's more prone to leaks on the 4008? Or perhaps a way to test for leaks without specialized equipment?

While a visual inspection is a good initial step, smaller leaks can be difficult to detect without proper equipment. Given the symptoms and error code, it is quite probable that the exhaust temperature sensor is faulty due to the leakage. Considering the potential impact on emission control and engine performance, I would suggest consulting a qualified workshop for a thorough diagnosis and sensor replacement.

I took it to a local mechanic, and after a smoke test, they found a small crack in the exhaust manifold. They replaced the exhaust temperature sensor and fixed the leak. The total repair cost came to around 265€. The car is running much better now – the check engine light is gone, the power is back, and fuel consumption seems normal again.