Method for diagnosing a wideband lambda sensor

A method for diagnosing electrical lines between a wideband lambda sensor and a control unit for a combustion engine, wherein the wideband lambda sensor includes a first electrical connector, a second electrical connector, a third electrical connector, an electromechanical pump cell connected between the first electrical connector and the second electrical connector, and an electrical calibration resistor connected between the second electrical connector and the third electrical connector, and wherein the control unit includes a first electrical input, a second electrical input, a third electrical input, a measuring resistor connecting the second input to the third input, an intermediate switch, a current source, which can be connected to the second input by the intermediate switch, a further switch;

• a reference potential;
• a reference resistor, wherein the reference resistor on the one hand can be connected via the further switch to the third input and to the measuring resistor and on the other hand is connected to the reference potential, and a measuring arrangement configured to measure a voltage drop across the measuring resistor, and wherein a first line connects the first connector of the wideband lambda sensor to the first input of the control unit, a second line connects the second connector of the wideband lambda sensor to the second input of the control unit, a third line connects the third connector of the wideband lambda sensor to the third input of the control unit, and the method comprising the following steps:
• measuring the voltage drop across the measuring resistor with intermediate switch closed and further switch open;
• and
• evaluating whether the second line is interrupted based on the voltage drop at the measuring resistor, and/or evaluating whether the third line is interrupted based on the voltage drip at the measuring resistor.

A method for determining a value of a calibration resistor of a wideband lambda sensor using a control unit, the control unit including a first electrical input, a second electrical input, a third electrical input, a measuring resistor connecting the second input to the third input, an intermediate switch, a current source, which can be connected to the second input by the intermediate switch, a further switch;

• a reference potential;
• a reference resistor, wherein the reference resistor on the one hand can be connected via the further switch to the third input and to the measuring resistor and on the other hand is connected to the reference potential, and a measuring arrangement configured to measure a voltage drop across the measuring resistor, wherein the wideband lambda sensor includes a first electrical connector, a second electrical connector, a third electrical connector, an electromechanical pump cell connected between the first electrical connector and the second electrical connector, an electrical calibration resistor connected between the second electrical connector and the third electrical connector, wherein a first line connects the first connector of the wideband lambda sensor to the first input of the control unit, a second line connects the second connector of the wideband lambda sensor to the second input of the control unit, and a third line connects the third connector of the wideband lambda sensor to the third input of the control unit, the method comprising the following steps:
• determining the value of the calibration resistor based on a first measurement of the voltage drop at the measuring resistor with intermediate switch closed and further switch closed and a second measurement of the voltage drop at the measuring resistor with intermediate switch closed and further switch open, and wherein the value of the calibration resistor is determined based on the first measurement and the second measurement in such a way that an influence of a resistance of the second line on a result is compensated.