Security systems
9.7.2 Security systems
Car and alarm manufacturers are constantly signal is being sent. They operate with one vehi- fighting to improve security. Building the alarm
cle only. Intrusion sensors such as car movement system as an integral part of the vehicle electron-
and volumetric sensing can be adjusted for ics has made significant improvements. Even so,
sensitivity.
retro fit systems can still be very effective. Three When operating with flashing lights most sys- main types of intruder alarm are used:
tems draw about 5 A. Without flashing lights (siren only) the current draw is less than 1 A. The
● switch operated on all entry points; sirens produce a sound level of about 95 dB, ● battery voltage sensed;
when measured 2 m in front of the vehicle. ● volumetric sensing.
Figure 9.30 shows a block diagram of a com- plex alarm system. The system, as is usual, can be There are three main ways to disable the
considered as a series of inputs and outputs. This vehicle:
is particularly useful for diagnosing faults. Most factory fitted alarms are combined with the central
● ignition circuit cut off; door locking system. This allows the facility men- ● starter circuit cut off;
tioned in a previous section known as lazy lock. ● engine ECU code lock.
Pressing the button on the remote unit, as well as setting the alarm, closes the windows and sunroof
Most alarm systems are made for 12 V, nega-
and locks the doors.
tive earth vehicles. They have electronic sirens
A security code in the engine ECU is a power- and give an audible signal when arming and dis-
ful deterrent. This can only be ‘unlocked’ to arming. They are all triggered when the car door
allow the engine to start when it receives a coded opens and will automatically reset after a period
signal. Ford and other manufacturers use a spe- of time, often one or two minutes. The alarms are
cial ignition key which is programmed with the triggered instantly when entry point is breached.
required information. Even the correct ‘cut’ key Most systems are two pieces, with separate con-
will not start the engine. Citroen, for example, trol unit and siren; most will have the control unit
have used a similar idea but the code has to be in the passenger compartment and the siren under
entered via a numerical keypad. the bonnet.
Of course nothing will stop the car being Most systems now come with two infrared
lifted on to a lorry and driven away, but this (IR) remote ‘keys’ that use small button type
technique will mean a new engine control ECU batteries and have an LED that shows when the
will be needed. The cost will be high and also
Electrical systems 219
questions may be asked as to why a new ECU is
ICE systems diagnostic chart
required.
Start
9.7.3 Mobile communications
Hand and eye checks (loose wires, loose switches
If the success of the cellular industry is any indi- and other obvious faults) –
all connections clean and
cation of how much use we can make of the tele-
tight. Check battery
phone, the future promises an even greater expansion. Cellular technology started to become Fuse continuity – and
supply to the set. Check
useful in the 1980s and has continued to develop
earth connection to the set
from then – very quickly. The need and desire we perceive to keep in
Check code is correct for
touch with each other is so great that an increas- the set (if appropriate) ing number of business people now have up
to five phone numbers: home, office, pager, fax Speaker resistance
No checks (refer to power but is
Set has
and cellular. But within the foreseeable future, specifications but
sound produced?
Yes
4 or 8 ⍀ are the
high tech digital radio technology and sophisti- most common).
Check speaker cables
cated telecommunications systems will enable all communications to be processed through a
Does the set
single number. suffer from
interference?
No
With personal numbering, a person carrying
a pocket-sized phone will need only one phone
Yes
number. Instead of people calling places, people Do all tuning
Aerial earth connection
and CD or tape No
will call people; we will not be tied to any particu- at the set – 0 ⍀
playback features
lar place. Personal numbering will make business work correctly?
Aerial earth connection
Clean tape heads if
people more productive because they will be able appropriate to reach and be reached by colleagues and clients, body – 0 ⍀
to the vehicle
anywhere and anytime, indoors or outdoors. When
Check ignition and
Yes
Ensure aerial is good
travelling from home to office or from one meeting
charging system for
quality
to the next, it will be possible to communicate with faults or missing
suppression devices
anyone, whenever the need arises.
Check connections to
But where does this leave communication sys- external devices like
multichangers or amps
tems relating to the vehicle? It is my opinion that ‘in vehicle’ communication equipment for nor-
End
mal business and personal use will be by the sim- ple pocket-sized mobile phone and that there is no further market for the car telephone. Hands
ICE, security and communication
free conversions will still be important.
system fault diagnosis table
CB radios and short range two-way systems such as used by taxi firms and service industries
will still have a place for the time being. Even Possible fault these may decline as the cellular network becomes
Symptom
Alarm does
Fuse blown
cheaper and more convenient to use.
not operate
Not set correctly Remote key battery discharged Open circuit connection to alarm unit ECU fault
9.8 Diagnosing ICE, security
Receiver/transmitter fault
and communication system Volumetric transmitter/receiver fault
Alarm goes
Drain on battery
faults
off for no
Loose connection apparent Vibration/trembler/movement reason
detection circuit set too sensitive
9.8.1 Testing procedure
Self-discharge in the battery Window left open allowing wind or even a
The process of checking an ICE system circuit is
bird or insect to cause interior movement
broadly as follows.
Somebody really is trying to steal the car …
220 Advanced automotive fault diagnosis
Radio Tracking HT components interference
Static buildup on isolated body panels High resistance or open circuit aerial earth Suppression device open circuit
ICE system Set not switched on! does not
Loose or open circuit connections produce sound
Trapped wires Connections to separate unit (amplifier, equaliser, etc.) incorrect Fuse blown
Unbalanced Fade or balance controls not set correctly sound
Speakers not wired correctly (front right, front left, rear right, rear left, etc.) Speaker open circuit or reduced output
Figure 9.31 Radio signals
Phasing Speaker polarity incorrect. This should be marked but if not use a small battery to
There are two overall issues to be considered
check all speakers are connected the same
relating to suppression of interference on a vehicle.
way. A small DC voltage will move the
These are as follows.
speaker cone in one direction
Speaker rattle ● Insecure speaker(s) Short range the effect of interference on
Trim not secure
the vehicle’s radio system.
Inadequate baffles
● Long range the effect of the vehicle on exter-
Crackling noises If one speaker – then try substitution
nal receivers such as domestic televisions.
If one channel – swap connections at the
This is covered by legislation making it illegal
set to isolate the fault
to cause disturbance to radios or televisions
If all channels but only the radio then check interference
when using a vehicle.
Radio set circuit fault
Interference can propagate in one of four ways:
Vibration Incorrect or loose mounting
Hum ● Speaker cables routed next to power line borne conducted through the wires;
supply wires
● air borne radiated through the air to the aerial;
Set fault
● capacitive coupling by an electric field;
Distortion Incorrect power rating speakers
● inductive coupling magnetic linking.
Poor radio Incorrect tuning reception
‘Dark’ spot/area. FM signals can be affected
The sources of interference in the motor vehi-
by tall buildings, etc.
cle can be summarised quite simply as any circuit
Aerial not fully extended
which is switched or interrupted suddenly. This
Aerial earth loose or high resistance
includes the action of a switch and the commuta-
Tuner not trimmed to the aerial (older sets generally)
tion process in a motor, both of which produce
Aerial sections not clean
rapidly increasing signals. The secret of suppres-
sion is to slow down this increase. Interference is
Telephone Low battery power
reception poor Poor reception area
produced from four main areas of the vehicle:
Interference from the vehicle
Loose connections on hands free circuit ● ignition system;
● charging system; ● motors and switches; ● static discharges.