Symptom(s): What the user/operator/repairer of the system (vehicle or what- ever) notices Fault

KOEC:
key on, engine cranking
KOEO:
key on, engine off
KOER:
key on, engine running
KS:
knock sensor
KSM:
knock sensor module
LT:
long term fuel trim
MAF:
mass airflow sensor
MAP:
manifold absolute pressure
sensor
MC:
mixture control
MDP:
manifold differential pressure
MFI:
multi-port fuel injection
MIL:
malfunction indicator lamp
MPH:
miles per hour
MST:
manifold surface temperature
MVZ:
manifold vacuum zone
NOX:
oxides of nitrogen
NVRAM:
non-volatile random access
memory
O2S:
oxygen sensor
OBD:
on-board diagnostics
OBD I:
on-board diagnostics generation
one
OBD II:
on-board diagnostics, second
generation
OC:
oxidation catalyst
ODM:
output device monitor
OL:
open loop
OSC:
oxygen sensor storage
PAIR:
pulsed secondary air injection
PCM:
powertrain control module
PCV:
positive crankcase ventilation
PNP:
park/neutral switch
PROM:
program read only memory
PSA:
pressure switch assembly
PSP:
power steering pressure
PTOX:
periodic trap oxidizer
RAM:
random access memory
RM:
relay module
ROM:
read only memory
RPM:
revolutions per minute
SC:
supercharger
SCB:
supercharger bypass
SDM:
sensing diagnostic mode
SFI:
sequential fuel injection
SRI:
service reminder indicator
SRT:
system readiness test
ST:
short term fuel trim
TB:
throttle body
TBI:
throttle body injection
TC:
turbocharger
TCC:
torque converter clutch
TCM:
transmission or transaxle con-
trol module
TFP:
throttle fluid pressure
TP:
throttle position
TPS:
throttle position sensor
TVV:
thermal vacuum valve
TWC:
three way catalyst
TWC ⫹ OC:
three way ⫹ oxidation catalytic
converter
VAF:
volume airflow
VCM:
vehicle control module
VR:
voltage regulator
VS:
vehicle sensor
VSS:
vehicle speed sensor
WOT:
wide open throttle
WU-TWC:
warm up three way catalytic
converter
xvi
Glossary

1.1 ‘If it ain’t broke, don’t
fix it!’
1.1.1 What is needed to find
faults?
Finding the problem when complex automotive
systems go wrong is easy, if you have the neces-
sary knowledge. This knowledge is in two parts:
●
understanding of the system in which the
problem exists;
●
the ability to apply a logical diagnostic routine.
It is also important to be clear about two defini-
tions:
●
symptom(s)
what the user/operator/repairer
of the system (vehicle or whatever) notices;
●
fault
the error in the system that causes the
symptom(s).
‘If it is not broken then do not go to the trouble
of repairing it,’ is the translation of this main sec-
tion heading! It’s a fair comment but if a system is
not operating to its optimum then it should be
repaired. This is where the skills come in to play.
It is necessary to recognise that something is not
operating correctly by applying your knowledge
of the system, and then by applying this know-
ledge further and combining it with the skills of
diagnostics, to be able to find out why.
Each main chapter of this book includes a
basic explanation of the vehicle system followed
by diagnostic techniques that are particularly
appropriate for that area. Examples of fault-
finding charts are also included. In the main, ref-
erences will be to generic systems rather than to
specific vehicles or marques. For specific details
about a particular vehicle or system the manufac-
turer’s information is the main source. Alterna-
tively ‘Autodata’ produce a fine range of books;
visit www.autodata.com for more details.
The knowledge requirement and the necessity
for diagnostic skills are further illustrated in the
next chapter.
Figure 1.1 shows a diagnostic procedure in
action!

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