Fiat 1996 Brava Service Manual page 346

Engine Bravo 0 ) * *
Fuel system 98 range
10.
DIAGNOSTICS
The complete fault diagnosis of the system can be carried out through an active dialogue using the diag­
nostic equipment.
If a fault is detected with the sensors, the electronic control unit replaces the data coming from the faulty
sensor with pre-memorized (recovery) data to allow the operation of the engine. If a fault is detected it is
permanently stored in the memory and the sensor is excluded from the system until the signal is com­
patible once again.
The same procedure is applied if the fault involves an actuator or control flap. The detection of a fault
and the replacement with recovery data involves the signalling of the fault by the specific warning light
in the instrument panel coming on.
The following parameters can, in the case of a failure, be managed by the control unit: flow meter,
coolant temperature sensor, butterfly casing actuator, Lambda sensor, air temperature sensor, battery
voltage and detonation sensors. In the case of faults in the control unit, the rpm sensor or the electric fu­
el pump, the system does not identify the fault and the vehicle stops. On request, the operator can read
the faults on the control unit using the diagnostic equipment.
Detecting faults
This is done whilst carrying out the basic function through which the sensor/actuator is managed.
Memorizing the error and the structure of the errors memory
Errors are memorized in the control unit in the order in which they occur. The location, type of error and
environmental conditions (specific for each type of error) are measured the moment the fault is detected
for all errors. There is also a frequency counter.
Classification of the defect
If a defect is recognized for the first time or the error state persists for a time t > 0.5s, the defect is memo­
rized as "permanent". If this defect later disappears, it is memorized as "intermittent" and "not present".
If it then reappears, it is memorized as "intermittent", but becomes "present".
The classification of a fault as "permanent" activates the recovery functions; when the fault disappears
the normal reading or implementation function is resumed.
Several types of fault are classified as "important", i.e. in terma of anti-pollution regulations. The pres­
ence of these faults is signalled to the driver by the failure warning light in the instrument panel coming
on.
Frequency counter
Each error is assigned a frequency counter, which is used to determine the moement in which a fault no
longer present has been memorized. The first time a fault is detected, the counter is set at 10. If the fault
disappears, the counter remains at the current value. If it reappears, it is increased by 1 (with an upper
limit 50).
The counter is decreased each time the engine is started up and the fault has not reappeared. If the
counter reaches zero, the fault is automatically cancelled from the memory.
If the counter has decreased and the fault reappears, the counter returns to 10 (if it was already above
10, it is not altered).
Signalling a fault
The failure warning light comes on when a defect is memorized as "present" and "important".
The delay time between detecting the fault and the warning light coming on is 0.1 seconds; the delay
time between the fault disappearing from the memory and the warning light going out is 4 seconds.
The warning light comes on each time the ignition key is turned to the ON position. If "important" faults
are aleady present, the warning light goes out after 4 seconds.
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