Pre-heating control unit

Pre-heating control unit

The operation of the heater plugs takes place via the pre-heating control unit, under the direct control of the electronic control unit. There is an "intelligent" relay inside which sends a return response (feed-back) to the injection control unit which is informed in this way of any failures of the pre-heating control unit or short circuit to earth of the heater plugs.

The diagram shows the connectors on the pre-heating control unit base and the relevant pin-out.

Connections

1. Vehicle earth
2. Not connected
3. Ignition switch (+15)
4. Electronic control unit (pre-post heating activation)
5. Electronic control unit (fault diagnosis)
6. Battery positive
7. Heater plugs
8. Heater plugs

Air temperature sensor

The intake air temperature sensor is, on this version, separate from the air flow meter: it comprises a standard NTC (Negative Temperature Coefficient) where the electrical resistance decreases as the temperature increases.

Since the control unit intake circuit is designed as a voltage divider, this voltage is divided between a resistance in the control unit and the sensor NTC resistance.

As a result the control unit is capable of evaluating the variations in the sensor resistance through the changes in voltage and thereby obtain information concerning the temperature.