Advanced Automotive Fault Diagnosis


 Heavy or light vehicles?



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Advanced Automotive Fault Diagnosis
LÔØI NOÙI ÑAÀU, ledklok
1.1.2 Heavy or light vehicles?
An important note about diagnostics is that the
general principles or techniques can be applied
to any system, physical or otherwise. As far as
heavy or light vehicles are concerned then this is
definitely the case. As discussed earlier, there is
a need for knowledge of the particular system,
but diagnostic skills are transferable.
1.2 Safe working 
practices
1.2.1 Introduction
Safe working practices in relation to diagnostic
procedures and indeed any work on a vehicle are
essential – for your safety as well as that of others.
You only have to follow two rules to be safe:

use your common sense – don’t fool about;

if in doubt – seek help.
Further, always wear appropriate personal protect-
ive equipment (PPE) when working on vehicles.
1
Introduction
Figure 1.1 Diagnostics in action


The following section lists some particular
risks when working with electricity or electrical
systems, together with suggestions for reducing
them. This is known as risk assessment.
1.2.2 Risk assessment and 
reduction
The following table notes some identified risks
involved with working on vehicles. It is by no
means exhaustive but serves as a good guide.
Identified risk
Reducing the risk
Battery acid
Sulphuric acid is corrosive so always use good
PPE – in this case overalls and if necessary
rubber gloves. A rubber apron is ideal, as are
goggles if working with batteries a lot
Electric shock
Ignition HT (high tension, which simply means
high voltage) is the most likely place to suffer a
shock, up to 25 000 V is quite normal. Use
insulated tools if it is necessary to work on HT
circuits with the engine running. Note that high
voltages are also present on circuits containing
windings due to back emf (electromotive force)
as they are switched off; a few hundred volts is
common. Mains supplied power tools and their
leads should be in good condition and using an
earth leakage trip is highly recommended
Exhaust gases
Suitable extraction must be used if the engine
is running indoors. Remember it is not just
the carbon monoxide (CO) that might make
you ill or even kill you, other exhaust compon-
ents could cause asthma or even cancer
Fire
Do not smoke when working on a vehicle.
Fuel leaks must be attended to immediately.
Remember the triangle of fire – (heat/fuel/
oxygen) – don’t let the three sides come
together
Moving loads
Only lift what is comfortable for you; ask for
help if necessary and/or use lifting equipment.
As a general guide, do not lift on your own if
it feels too heavy!
Raising or 
Apply brakes and/or chock the wheels and 
lifting vehicles
when raising a vehicle on a jack or drive on
lift. Only jack under substantial chassis and
suspension structures. Use axle stands in case
the jack fails
Running 
Do not wear loose clothing; good overalls 
engines
are ideal. Keep the keys in your possession
when working on an engine to prevent others
starting it. Take extra care if working near
running drive belts
Short circuits
Use a jump lead with an in-line fuse to prevent
damage due to a short when testing.
Disconnect the battery (earth lead off first and
back on last) if any danger of a short exists. A
very high current can flow from a vehicle bat-
tery, it will burn you as well as the vehicle
Skin problems
Use a good barrier cream and/or latex gloves.
Wash skin and clothes regularly

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