Method, computing unit, and computer program for determining an amount of hydrocarbons in an exhaust gas of a lean-operation internal-combustion engine

A method () for determining an amount of hydrocarbons in an exhaust gas () downstream of a lean-operation internal-combustion engine (), comprising the following steps: observing a first catalyst heating mode of the internal-combustion engine () at a high catalyst temperature, wherein a predefinable amount of fuel having a predominantly non-combusting portion is introduced into a combustion chamber of the internal-combustion engine (); determining an actual temperature change downstream of an oxidation catalyst () downstream of the internal-combustion engine () during the first catalyst heating mode; and determining the amount of hydrocarbons (cHC) in the exhaust gas () upstream of the oxidation catalyst () based on the actual temperature change. Furthermore, a computing unit () and a computer program for carrying out such a method () are proposed.