TABLE OF CONTENTS Sensors and actuators have a chapter all to themselves because they are so important! And also because the issues and diagnostic techniques are common to many systems. For example, the testing procedure for an inductive engine speed sensor on a fuel injection system, is the same as for an inductive speed sensor on an ABS system.
Testing sensors to diagnose faults is usually a matter of measuring their output signal. In some cases the sensor will produce this on its own (an inductive sensor for example). In other cases, it will be necessary to supply the correct voltage to the device to make it work (Hall sensor for example).
| Note | It is normal to check that the vehicle circuit is supplying the voltage before proceeding to test the sensor. |
After the description of most sensors, and actuators a table is included listing the sensor, equipment necessary, test method(s), results of the tests and a scope waveform. A waveform will be reproduced where appropriate, as this is often the recommended method of testing (see Chapter 4 for more details). The waveform shown will either be the output of a sensor or the signal supplied to an actuator.
| Note | Any figures given are average or typical values. Refer to a good reference source such as a workshop manual, or Autodata for specific values. Sensor and actuator waveforms are shown in Chapter 7. |
Thermistors are the most common device used for temperature measurement on the motor vehicle.
