Fiat 1998 Marea Weekend, Service Manual

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Engine
Marea-Marea Weekend® ^
Fuel system
1998 range
10.
Controlling knock
This function detects the presence of knock by processing signals from relevant sensors. The ECU con-
tinually compares signals from sensors with a threshold level which is continually updated in turn to
take into account background noise and engine age.
If the system detects the presence of knock, the strategy reduces the ignition advance until the phe-
nomenon disappears. The advance is then gradually restored to the base setting or until knock recurs.
Advance increases are implemented gradually, whereas reductions take place immediately.
When accelerating, a higher threshold is used to take into account increased engine noise in these cir-
cumstances.
The knock control strategy is also self-adaptive. This means that advance reductions repeated regularly
are memorised in order to adjust mapping to the range of conditions experienced by the engine (use of
low-octane fuel, for example). The strategy is able to restore the advance setting to the mapped level
when the conditions that gave rise to the reduction cease.
FIAT CODE IGNITION IMMOBILISER MANAGEMENT
The system features an anti-theft function. This is implemented through a special FIAT CODE control
unit able to dialogue with the engine control unit, and an electronic key with a specific sender unit de-
signed for sending an identification code.
Once the key has been turned to STOP, the FIAT CODE system de-activates the engine control unit
completely.
When the key is turned to MAR, the following operations take place in sequence:
1 - the engine control unit (whose memory contains a secret code) sends the FIAT CODE a request de-
manding that a secret code be sent to de-activate the function lock:
2 - the FIAT CODE control unit responds by sending the secret code only after receiving a recognition
code sent by the ignition key;
3 - recognition of the secret code allows the engine control unit lock to be de-activated and normal op-
eration to proceed.
NOTE Due to the presence of the FIA T CODE immobiliser, DO NOT T E S T the vehicle using another
engine control unit. In this case, the FIA T CODE control unit would transfer the recognition
code (unknown) to the test control unit, which would thus be rendered completely unservice-
able on other vehicles.
RADIATOR FAN MANAGEMENT
The ECU controls radiator fan operation directly according to coolant temperature and whether the air
conditioning system is activated or not.
The fan comes on when the temperature exceeds 97 °C (1st speed) and 102 °C (2nd speed). The fan
goes off with a hysteresis of 3 °C lower than the activation threshold.
High and low speed functions are controlled by specific relays located in the air conditioner control unit
and controlled by the control unit.
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Publication no. 506.763/09