Professional Corner

Diagnostic - Lambda Sensor Tester

Basic procedure

Check the Lambda sensor circuit

• Ensure that the tester is connected to the sensor
• Measure sensor output voltage when the engine is running at normal speed and at normal operating temperature.

Key indicators

Correctly functioning sensor

• The voltage output indicator will move continuously between the lean and the rich scale readings range.

Incorrectly functioning sensor

• The voltage readout will remain in either the lean or rich scale range.

Diagnosis

If the sensor is functioning incorrectly, the tester should be used to simulate different conditions. The tester sends an artificial Lambda signal output to the ECU:

• When the sensor sends a "rich" signal the ECU should respond by leaning out the mixture
• When the sensor sends a "lean" signal, the ECU should respond by richening the mixture.

Conclusions:

• If the ECU does not respond correctly, there is a problem with the ECU
• If the Ecu responds correctly, there is a problem with the Lambda Sensor itself.