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.