Lambda Sensor - Fiat Bravo Service Manual

E n g i n e
Fuel system
10.
0,995
mV
1000
800
600
400
200
1 1 1
0,7 0,8 0,9 1,0 1,1 1,2
X=1 Ideal mixture (stoichiometric)
X 1 Lean mixture
Excess air; the CO values tend to be low
X 1 Rich mixture
Lack of air; the CO values tend to be high
Wiring connector
24
1,005
X
*-
t
T 1 1 1
1,3
Bravo-Brava
LAMBDA S E N S O R
The Lambda sensor measures the oxygen
content in the exhaust gases: it is fitted on the
exhaust pipe upstream of the catalytic s i -
lencer.
The sensor output signal is sent to the control
unit for fee-back correction of the mixture
strength.
When the sensor provides a low signal (volt-
age below 2 0 0 mV), the control unit recog-
nizes a lean mixture and increases the injec-
tion time; later, w h e n the sensor signal is high
(voltage above 800 mV), the control unit rec-
ognizes a rich mixture and decreases the i n -
jection time.
This sequence is repeated at a frequency in
order of tens of Hertz so that the engine c o n -
stantly operates w i t h a mixture strength close
to the stoichiometric ratio.
For temperatures below 300 °C, the ceramic
material is not activated, therefore the sensor
does not send plausible signals: to ensure
rapid heating during starting and maintain
the temperature during idling, the sensor is
fitted with a heater with the electrical resis-
tance always switched on.
The sensor can rapidly be put out of
action by the presence of even slight
amounts of lead in the fuel.
The sensor heater resistance can be mea-
sured by disconnecting the connector and
connecting an ohmmeter as shown in the d i -
agram.
Resistance: 4.5+0.5 ohm at 20 °C
iggi
lev
98 range
Print no. 506.670/16