Electrochemical sensor

A method for determining a lambda value of a gas mixture in an internal combustion engine, comprising the steps of:

• providing an electrochemical sensor which has an electrochemical element for measuring a gas concentration of the gas mixture contained in a first gas chamber, the electrochemical sensor including:
• an electrochemical pump cell including a first solid electrolyte body, a first electrode, a second electrode and a second gas chamber, the second gas chamber communicating with the first gas chamber via a gas inlet opening, wherein one of the first electrode and the second electrode is situated in the second gas chamber, and
• an electrochemical sensor cell including a second solid electrolyte body, a third electrode, a reference gas chamber and a fourth electrode situated in the reference gas chamber, the reference gas chamber cooperating with a reference gas duct, the fourth electrode having a supply conductor which is provided for an electrical connection and which includes an electrically insulating layer, the electrically insulating layer being disposed, at least in part, in the reference gas duct and insulating the supply conductor from the second solid electrolyte body, wherein the reference gas chamber and the reference gas duct are inside the second solid electrolyte body and outside the first solid electrolyte body;
• and
• determining the lambda value using the electrochemical sensor.