Fiat 1996 Brava Service Manual page 474

Engine Bravo-Brava @t i*
Fuel system '98 range
10.
FAULT DIAGNOSIS
Full diagnosis of the fuel injection-ignition is possible by active dialogue with the Examiner or SDC sta­
tion.
If faults in the sensors are detected, the electronic control unit replaces the data coming from the faulty
sensor with pre-memorized data (recovery) to allow the engine to continue operating.
Detection of the fault leads to its permanent storage in memory and the exclusion of the sensor from the
system until the signal becomes compatible again.
The same procedure is applied if the fault affects an actuator or its control port. The detection of the fault
and the replacement with recovery data leads to indication of a fault by the warning light on the instru­
ment panel coming on.
The devices which, in the event of a fault, can be managed by recovery from the control unit are:
- Idle speed actuator - Coolant temperature sensor
- Ignition coils - Knock sensor
- Fuel vapour recirculation solenoid - Throttle position sensor
- Air temperature and pressure sensor - Lambda probe
In the event of faults in the control unit or rpm sensor, the system, even though it detects the fault, can­
not replace it with recovery data and the car stops. The faults can be detected in the memory of the con­
trol unit using the Examiner or SDC station.
Error recognition and memorization
The error is detected via a system of validations which operates as follows.
When an error is detected, this is checked for a certain period of time to avoid possible interference on
the diagnostic line. If the fault passes this stage, it is considered to be present and is stored in RAM (fil­
tered error). It is then checked that the error remains present for a further period of time (called validation
time); if this stage is also passed, the error is finally memorized (validated error) and the fault warning
light comes on. The stage of writing the error in EEPROM takes place after the ignition is switched off.
Error frequency counter
A frequency counter is assigned to each error in order to determine the moment when a fault which is no
longer present was memorized. On first detection of a validated error, the counter is set to a fixed set val­
ue.
The counter is decremented whenever the car is started without the fault reappearing. If the counter
reaches zero, the fault is automatically deleted from EEPROM.
Error deletion
Errors can be deleted from EEPROM in two ways:
- by means of the diagnostic equipment (Examiner or SDC station), in active diagnosis
- by resetting the error frequency counter.
NOTE Disconnecting the control unit from the system, even for long periods, does not delete data
recorded in the EEPROM.
Management of the system fault warning light
To check its operation, the control unit lights up the warning light and leaves it on for about 4 seconds
whenever the ignition is switched on. The warning light then comes on whenever there is a validated er­
ror, i.e. for as long as the fault situation remains, and it goes out when the fault disappears.
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Publication no. 506.670/14