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Glossary of terms you will come across during your Phase 2 training.

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This identifier indicates the type of failure that is associated with the component. The FMI has been adopted from the SAE practice of J1587 diagnostics. The FMI follows the parameter identifier (PID) in the descriptions of the fault code. The descriptions of the FMIs are in the following list:

0 - The data is valid but the data is above the normal operational range.

1 - The data is valid, but the data is below the normal operational range.

2 - The data is erratic, intermittent or incorrect.

3 - The voltage is above normal or the voltage is shorted high.

4 - The voltage is below normal or the voltage is shorted low.

5 - The current is below normal or circuit is open.

6 - The current is above normal or the circuit is grounded.

7 - The mechanical system is not responding properly.

8 - There is an abnormal frequency, an abnormal pulse width, or an abnormal time period.

9 - There has been an abnormal update.

10 - There is an abnormal rate of charge.

11 - The failure mode is not identifiable.

12 - The device or the component is damaged.

For example, in the diagnostic code: 110 - 3, the 110 is the CID, in this case, the coolant temperature sensor. The 3 is the Failure Mode Identifier (FMI), in this case, voltage high.


the SI unit of electrical capacitance, equal to the capacitance of a capacitor in which one coulomb of charge causes a potential difference of one volt.

The farad is named after Michael Faraday, and the unit of measurement is represented by the capital letter 'F'

The farad is a huge amount of capacitance, so more common measurements are:

  • the microfarad, where 1μF=10-6F or 0.000001F
  • the nanofarad, where 1nF=10-9F or 0.000000001F

Example of use on Phase 2:

During the glow plug time delay circuit exercise, you will us an electrolytic capacitor with a value of approximately 2000 microfarads, or 2000 μF or 0.002F 


Foras Áiseanna Saothair: Irish for Training and Employment Authority.

FÁS is Ireland's National Training and Employment Authority.

FÁS Training Centre, Cabra.


Feeler bladesMeasuring blades used by cp fitters to accurately measure small distances between components. For example, feeler blades are used when setting valve clearances in an engine:

Setting valve clearance using feeler blades

A metal containing iron. Examples are pig iron, wrought iron, cast iron and steel.

Field coils are used in motors. They are called field coils because they consist of a soft iron core, around which is wrapped coils of wire (coils). When electricity is passed through these coils of wire, a magnetic field is produced (field) - hence the term 'field coils'.

Starter motor field coils.

Unlike a bipolar junction transistor (BJT), the field effect transistor (FET) is a voltage-controlled transistor in which the source to drain conduction is controlled by the gate to source voltage.

Alternator rotor.

In the context of alternators, field excitation is the act of passing electrical current through the windings on the rotor. The more current we pass through these windings, the stronger the magnet we produce, and the more electricity we generate. In order to regulate the voltage, we switch on and off this field circuit with a voltage regulator.


Often (incorrectly) referred to as the "diff", the final drive is where drive coming down the propeller shaft is:

  • Reduced in speed and increased in torque by means of having a small pinion drive a large crownwheel.
  • The drive is turned through 900 in order to reach the driving wheels via the halfshafts.

Final drive and halfshaft.

These are the two functions of the final drive. This unit usually has the differential gears mounted on it. The funcion of the differential is to allow the driving wheels to turn at different speed but always equal torque.


Final Drive Differential Unit

Correct name of the unit of a live (driving) axle on a vehicle. The unit is sometimes referred to as the "diff", "differential" or the "final drive", when, in actual fact the unit is a combination of both these components.

There is a crown wheel and pinion which is the final drive. The functions of this unit are:

  • To carry out the final speed reduction and torque increase of the power going to the road wheels.
  • To turn drive through 900, from the propeller shaft to the half shafts.

There is also a cluster of gears known as the differential. The function of the differential is to allow the driving wheels to turn at different speeds, but always equal torque.

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