| CPC F01N 11/007 (2013.01) [F01N 3/2033 (2013.01); G07C 5/0808 (2013.01); G07C 5/0816 (2013.01); F01N 2550/05 (2013.01)] | 9 Claims |

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1. A method (200) for diagnosing the functionality of a burner (100) in an exhaust gas system of an internal-combustion engine (1) of a motor vehicle, the method comprising:
receiving, at a computing unit, a signal (325) from a lambda sensor in the exhaust gas system,
determining, with the computing unit, a lambda value (210) of an exhaust gas of the burner (100) based on the received signal (325),
comparing (220), with the computing unit, the determined lambda value to a time- based changing lambda threshold (225),
detecting, with the computing unit, a malfunction (280) of the burner when the
determined lambda value exceeds the time-based changing lambda threshold (225), and
performing a measure with the computing unit when the malfunction is detected (280),
wherein the time-based changing lambda threshold (225) decreases as a function of a time elapsed since an operational start of the burner (100), and
wherein the measure comprises outputting, with the computing unit, an alert.
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