Checking resistance

a. Electrode (+) in contact with outside air b. Electrode (-) in contact with exhaust gas 1. Ceramic case 2. Protective pipe 3. Metal case 4. Electrical resistant When the probe supplies a low voltage level (less than 200 mV) the ECU recognises that the mixture is lean (lambda » 1) and takes steps to increase the amount of fuel injected. When the probe supplies a high voltage level (greater than 800 mV) the control unit recognises that the mixture is rich (lambda « 1) and decreases the quantity of fuel injected. The lambda probe therefore alters injection times to ensure that the engine operates with a lambda factor continually fluctuating between 0.980 and 1.020. Below 300 °C the ceramic material is not active and the probe does not send usable signals. A special circuit in the control unit blocks loop mixture regulation while the probe is warming up. To ensure service temperature is reached quickly, the probe is equipped with electrical resistance (4) supplied by the battery

The probe may be swiftly put out of service by even slight traces of lead in the fuel. Operation should be checked at 45,000 and 90,000 km in accordance with the programmed maintenance plan.

Checking resistance

The heater and probe resistance may be measured by disconnecting the connector and connecting an ohmmeter as indicated in the figure. Heater resistance (A) = 4.3 - 4.7 ohm Probe resistance (B) = 5000 ohm (max)

Recovery

Lambda data are ignored (open loop).

Wiring connector

The numbers in boxes indicate the corresponding control unit pins.