Autodiagnosis and alternative function

The air temperature and pressure sensor is an integrated component which has two functions: one of reading the pressure in the inlet manifold and the other of measuring the temperature of the air inside the inlet manifold. Both pieces on information are used by the injection control unit to define the quantity of air drawn in by the engine; this information is then used to calculate the injection time and the ignition point. The sensor is fitted on the inlet manifold.

Autodiagnosis and alternative function

When the pressure sensor signal starts to fail, the butterfly potentiometer and the rpm signals are used to calculate the injection time; when suitably processed by the M.P.I. control unit, these signals make it possible to reconstruct the missing signal (recovery function). If the air temperature sensor is broken, the M.P.I. control unit uses a recovery temperature figure of 50 °C stored in its memory and the mixture strength self-adjustment is disabled.

The autodiagnostic function controls the two sensor output signals.
It recognizes the following for both signals:
- Short circuit to earth.
- Short circuit to the positive and reference voltage.
- Open circuit/break.

WATER TEMPERATURE SENSOR

This is an NTC type sensor, i.e. as the temperature increases, the resistance decreases; it is connected to the control unit via the connector shown below at the side.

Electrical features

The dynamic characteristics of the sensor can be measured using an ohmmeter and are as follows:

20°C = 3541-3953 ohm
50°C = 1011-1149 ohm
90°C = 252-298 ohm

Recovery

In case of a sensor failure, the control unit activates the following strategies:
Air temperature below 20°C: water temperature = air temperature, with an increase of 10°C/min up to a maximum of 80°C
Air temperature above 20°C: water temperature = 80°C
If the air temperature is faulty: water temperature = 80°C