Method for diagnosing electrical lines (201, 202, 203, 204) of a broadband lambda probe, wherein the electrical lines (201, 202, 203, 204) of the broadband lambda probe are connected to a connection (RE, IPN, APN, MES) of an evaluation and control unit, wherein the evaluation and control unit is, in particular, in the form of an ASIC and is designed to operate a broadband lambda probe, wherein the broadband lambda probe has electrical lines (201, 202, 203, 204), wherein the evaluation and control unit has electrical connections (RE, IPN, APN, MES) for electrical connection to the electrical lines (201, 202, 203, 204) of the broadband lambda probe, wherein the evaluation and control unit has four electrical connections (RE, IPN, APN, MES), via which it is connected to four electrical lines of the broadband lambda probe, and the four electrical lines (201, 202, 203, 204) of the broadband lambda probe lead to electrodes of an electrochemical Nernst cell and of an electrochemical pump cell of the broadband lambda probe and to an ohmic resistor of the broadband lambda probe, wherein the evaluation and control unit has a device for determining a target value (Iq) of a current flowing into the electrical connections (RE, IPN, APN, MES) and for comparing this target value (Iq) with the current (Ip) actually flowing into the electrical connections, and wherein the evaluation and control unit has comparators (130, 130') for comparing the electrical potential (Up) applied to the electrical connections with predefined limits (L1, L2); wherein the diagnosis provides for the presence of a short circuit or shunt circuit of one of the electrical lines (201, 202, 203, 204) to be excluded precisely when neither the electrical potential (Up) applied to the associated connection (RE, IPN, APN, MES) is outside predefined limits (L1, L2) nor the electrical current (Ip) flowing into the associated connection (RE, IPN, APN, MES) differs from a target value (Iq, I'q) by more than a threshold value; and/or a short circuit or shunt circuit of one of the electrical lines (201, 202, 203, 204) is inferred precisely when at least one of the following conditions is met: - the electrical potential (Up) applied to the associated connection (RE, IPN, APN, MES) is outside predefined limits; - the electrical current (Ip) flowing into the associated connection (RE, IPN, APN, MES) differs from a target value (Iq, I'q) by more than a threshold value; wherein the diagnosis is cyclically carried out for all lines (201, 202, 203, 204) by means of the method. a short circuit or shunt circuit of one of the electrical lines (201, 202, 203, 204) is inferred precisely when at least one of the following conditions is met: - the electrical potential (Up) applied to the associated connection (RE, IPN, APN, MES) is outside predefined limits; - the electrical current (Ip) flowing into the associated connection (RE, IPN, APN, MES) differs from a target value (Iq, I'q) by more than a threshold value; - the electrical potential (Up) applied to the associated connection (RE, IPN, APN, MES) is outside predefined limits; - the electrical current (Ip) flowing into the associated connection (RE, IPN, APN, MES) differs from a target value (Iq, I'q) by more than a threshold value; wherein the diagnosis is cyclically carried out for all lines (201, 202, 203, 204) by means of the method.