The Lambda Sensor or Oxygen Sensor is used by the ECU to display Air Fuel Ratios AFR and optimize the fuel economy after the vehicle has been tuned. Note: In the ECU software it shows a voltage signal and not the actual AFR value. The reason is that the ECU is not a tuning tool with calibration software. It is merely using the sensor for control purposes which is tuned to the correct mixture.

Different Lambda sensors
1 to 4 wire sensors are normally narrow band sensors. Their signal could be used directly in the ECU as it is a 0.1 volt to 0.9-volt signal. The 5 and 6 wire sensors require driving electronics and give a 0 to 5-volt signal out for the ECU. This wideband signal could be used by the ECU.

Testing a Lambda sensor for the correct Pin-outs
Test the resistance with an Ohm Meter between two pins at a time. The heater element normally has the same colors and has a resistance of 6 to 12 ohm. Connect the element wires to earth and 12 volts as above. The element does not have a specific polarity. The sensor output can only be measured while the engine is running. Connect the two remaining wires to the ECU signal input wires as indicated on the drawing. The sensor will only give an output when the engine has achieved some temperature. If the sensor is not working, swop the signal and earth wires and test again. The sensor will not be damaged if the earth and signal output has been swopped.

Life expectancy.
The life expectancy of a lambda sensor varies due to fuel type and application. On unleaded fuel around 500 hours. Very rich mixtures will shorten sensor life. Lambda sensors can be damaged by gasket sealants, anti-seize and some fuel additives.

Position
The ideal position for mounting the lambda sensor is at least half a meter from the engine and after the exhaust collector or turbo down pipe. The lambda should be orientated on the top or side of the pipe. Never at the bottom!

Sample Sensor Pin outs