Fiat Bravo Service Manual page 381

Engine
Fuel system
10.
Bravo $
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AIR TEMPERATURE
(0.280.130.073)
SENSOR
The intake air temperature sensor is, in this
version, separate from the air flow meter: it is
made up of an NTC sensor (Negative Tem­
perature Coefficient) where the electrical re­
sistance decreases as the temperature in­
creases.
Since the control unit input circuit is de­
signed as a tension divider, this tension is di­
vided between a resistance in the control unit
and the sensor NTC resistance. As a result the
control unit is capable of evaluating the vari­
ations in the resistance of the sensor through
the changes in voltage and of thereby obtain­
ing the temperature information.
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Recovery
If, 3 minutes after starting, the control unit
detects a temperature (air T) < -35 °C or >
130 °C for 30 seconds, it assumes air T=20.4
°C as a fixed parameter
Additional provisions
Locking the self-adjustment of the mixture
strength at current values
Wiring connector
NOTE The numbers indicate the corre­
sponding control unit pins.
1. Air temperature sensor
2. Flow meter
FLOW METER (0.280.217.111)
The air flow meter is the "heated film" type;
the operating principle is based on a heated
diaphragm which is placed in a measuring
duct through which the intake air entering
the engine flows.
The film diaphragm is kept at a constant tem­
perature ( ~ 120 °C above the temperature of
the air) by the heating resistance in contact
with it.
The mass of air which passes through the
measuring duct tends to remove heat from
the diaphragm therefore, to maintain the lat­
ter at a constant temperature, a current must
flow through the heating resistance; this cur­
rent is measured by a suitable Wheatstone
bridge.
The current measured is therefore propor­
tional to the mass of air flow.
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Print no. 506.670