Fiat Bravo Service Manual page 461

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When the probe provides a low voltage level (below 200 mV), the control unit recognizes that the mix-

ture strength is weak (lambda »1) and increases the quantity of fuel injected. When the probe provides a

high voltage level (over 800 mV), the control unit recognizes that the mixture strength is rich (lambda «

1) and reduces the quantity of fuel injected.

The Lambda probe thus varies the injection times so that the engine operates with a Lambda coefficient

constantly fluctuating between about 0.980 and 1.020.

For temperatures below 300°C the ceramic material is not active, so the probe does not send usable sig-

nals and a particular circuit present in the control unit blocks the closed loop adjustment of the mixture

strength during the warming up of the probe.

To ensure that operating temperature is quickly reached, the probe has a heating element (4) supplied

by the battery.

The probe can be quickly put out of service by even small quantities of lead in the fuel.

Checking the resistance

The resistance of the heater and probe can be

measured by disconnecting the connector

and connecting an ohmmeter as s h o w n in

Heater resistance = 4.3 - 4.7 ohm

The Lambda data are ignored (open loop).

Wiring connector

The numbers in boxes indicate the corre-

sponding control unit pins.

Electrode ( + ) in c o n -

tact w i t h the external

Electrode (-) in c o n -

tact w i t h the exhaust

Ceramic casing

Protective pipe

Metal casing

Heating element