g. Autodiagnosis

g. Autodiagnosis

The control unit is equipped with an autodiagnostics system which allows it to constantly check its operation and that of the sensors/actuators connected to it.

If the values detected by the sensors/actuators are outside of the tolerances, the system recognizes the problem and replaces the irregular values with suitable ones to ensure emergency operation (recovery) until the first service centre can be reached (limp-home).

The errors are recognized with: the ignition key in the ON position, during starting, with the engine running and the vehicle moving; they are memorized in the control unit in the order in which they occur. For each error the following is memorized: the location, the type and the frequency. The defect can be catalogued as permanent or intermittent; in the case of a “permanent error” the recovery strategy is implemented.

There is a frequency counter for each error to determine the moment in which a fault which has been stored in the memory is no longer present. When the problem is first detected the frequency counter memorizes a value equal to 10.

The counter is decreased each time the engine is started up and the fault has not reappeared; if the counter reaches 0 then the fault is automatically cancelled from the memory.

If after the counter has decreased the fault should reappear then the counter is always returned to the value 10.

The errors memory is cancelled either by means of a specific F/L Tester command or by interrupting the control unit supply (disconnecting the battery or the control unit connector).

The control unit ensures the supply of the engine using different strategies or fixed reference values if it acquires signals which are not plausible from one or all of the following components:

• - engine idle speed regulator,
• - idle contact,
• - butterfly position sensor,
• - coolant temperature sensor,
• - intake air temperature sensor,
• - Lambda sensor.

Engine idle speed regulator

The control unit is equipped with an emergency/safety function which is rendered operational by the closing of the idle contact.

In this condition, if the vehicle is driven with butterfly opening angles (α) in the range of the first potentiometer track (0° - 24°), then the maximum engine speed is limited to 2000 rpm.

When 2000 rpm is reached, the electronic control unit constantly cuts off and restores the injection of the fuel.

The driver of the vehicle will be aware of the implementation of the emergency conditions because the engine will tend to accelerate and decelerate.

If, at this point, the accelerator pedal is operated until the butterfly valve opening angle (α) reaches the potentiometer second track conditions (≥ 22°), the injection of the fuel is restored and the operation of the engine becomes smooth once again.