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Technical Topics

"Security ECU’s keys and codes

In an effort to improve vehicle security, modern fuel computers use a system that talks to the ignition key. Simply turning the lock tumbles to release the steering lock will do nothing to unlock the fuel computer. A second electronic lock must be decoded to energise the fuel computer brain, as the fuel computer talks to the ignition key. The ignition key carries a special code similar to the credit card PIN system. Coding ECU’s to the ignition key has been very successful at defeating our car theft problems.

These sophisticated computer systems, introduced to help prevent vehicle theft, have presented a nightmare to the motor trade. Swapping fuel computers to test a modern system result in total brain failure as the test computer receives unrecognisable codes exchanged between ignition key, ECU and other electronic components, depending on the manufacturer.

For many vehicles, if a fuel computer is swapped and the wrong ignition key signal is received at the fuel computer, the computer will shut down and become useless.Think twice before you swap once, it will get very expensive!.

  What is Lambda 1


When the engine is operating at normal running temperature a Lambda sensor or Exhaust Oxygen Sensor, situated in the exhaust close to the engine, is used to control fuelling. This sensor for 95% of engine operation is in total control of the fuel mixture settings. When the exhaust gasses are in perfect balance for the catalytic converter to be 100% successful at cleaning the exhaust gas, the engine is operating at Lambda = 1

For the cat to operate successfully this sensor tries to hold the fuelling around Lambda = 1. Operating at this point the converter will reduce all the exhaust emissions to, Carbon Dioxide, Oxygen and Water. Whilst the specifications for vehicles may vary a Lambda measure outside values of 1.03 to 0.097 may result in a failure of the MOT test.

Modern fuel injected vehicles operate at Lambda = 1. For a quality engine the catalytic converter does very little, however it is that little bit which is an MOT pass or fail. As the engine wears and produces more undesirable gas conversion becomes more important and the converter has to work overtime.

At this point a successful but poor converter on a new car would fail on a high mileage vehicle.

·        A poorly maintained engine

·        A high mileage vehicle

·        A defective lambda sensor

·        A poor exhaust pipe, leaking a bit

·        Engine electronic control systems

Any of the above can result in an MOT failure.


Oil Change

With the exception of regular oil changes, most modern engines are becoming almost maintenance free. One of the refinements fitted to achieve reduced servicing requirements is the hydraulic tappet. Through hydraulics, the need to adjust valve clearances has been eliminated.

The camshaft which operates the valves acts on a hydraulic plunger. With the camshaft off the hydraulic plunger oil can flow into the hydraulic tappet. When the camshaft starts to move the tappet down, the oil's passage way is closed. Oil in the plunger is now compressed by the cam which in turn opens the inlet or exhaust valve.

The oil's passage way into each hydraulic tappet is very small. Over a period of time the oil's passage ways will become clogged and the tappet efficiency will falter.


A good quality motor oil, of the recommended viscosity, is essential. A consistent viscosity (oil thickness) over the engine temperature operating range is crucial for consistent engine operation performance. Such qualities are best found with the more expensive oil product ranges.

When performing an oil change the use of an engine flush will help to remove lacquer build up on the tappet oil's passage ways.

Manufactures may quote ever increased intervals between oil changes, but ask any motor technician the period their vehicles are run between oil changes, few will stretch oils over 10,000 miles.

Battery Care

Batteries often die in cold weather.

The battery generates electricity using a chemical process. This chemical process slows as the battery temperature falls. A battery which struggles in warm weather will have little hope of successfully starting a vehicle during the Winter months. The battery's efforts to start a cold engine are further frustrated because the motor oil thickens as it becomes colder. This problem is irritated by old or poor quality motor oils.

Batteries will typically last from 2 to 5 years depending on many factors including luck, however some points to consider which may help are:

· Keep the battery fully charged when off a vehicle. If you have a spare which has been lying around the shed for a year neglected it is probably useless.

· Avoid bumpy road conditions as shaking the battery about will reduce its life expectancy.

· Most batteries gracefully die of old age and Winter operating conditions conclude their useful life, however some will fail spontaneously without warning.

· Just because your vehicle appears to have battery problems check the charging system before you purchase a new battery. Replacing the battery is not always a cure for poor starting.

Don't drive in poor weather without your headlight on to save the battery. Modern vehicles are easily capable of charging the battery and operating the lights on any reasonable run. If you need to compromise your vehicle's lighting you have a serious problem which will result in system failure, and should have the charging system professionally tested.



If you think that antifreeze is only required in the winter, you should keep reading...

Antifreeze is a poor word to describe the complex composition of a quality product. Far better to use the term coolant as the requirements of a complex cooling system don't vanish with Winters frosts.

With a suitable pressure cap on the system, typical quality coolants having 50% antifreeze : water mix will provide protection from minus 38 degrees C to 130 degrees C, lowering the freezing point and raising the boiling point. Therefore the basic function of protection against freezing is matched with equal importance during Summer months when stuck in a traffic jam, of raising the boiling point. You may look around in a traffic jam and see motorists with their bonnet up and steam pouring out of the engine cooling system. Should you fail to maintain the vehicle cooling system, you may also end up on the hard shoulder with a steaming engine.

Modern engine design incorporates the use of lightweight products such as aluminium. Without protection aluminium engines and cylinder heads will oxidise and crumble into the cooling system. The aluminium oxide will clog the radiator and the car internal heater matrix. Modern design has produced ever smaller radiators reducing the size of water ways through the heat exchanger. Once blocked the radiator efficiency is lost and you will not have to find a traffic jam for the system to boil over during the hot Summer months.

The gasket which separated engine top and bottom is made up of laminated materials. Aging coolant becomes acidic and will eat into this head gasket, coursing engine failure, (water in the oil).

Replacing the coolant at recommended intervals is part of a quality service schedule.

Don't neglect your vehicle's maintenance and enjoy a trouble free cooling system for all twelve months of the year

Cam Belt Care

The cam belt will synchronis the engine mechanical systems, valves and pistons.

At best a defective cam belt will cause the engine to stop without warning. Depending on engine design the failure may result in total engine destruction.

The cam belt is responsible for the timing, opening and closing of the engine valves. The valves are responsible for allowing air into and exhaust gases out of the engine. If the cam belt fails (snaps) some of the valves will be left in an open position, which the piston normally occupies at the top of its travel. With the valve and piston trying to occupy the same engine space at the same time disaster is inevitable.

Generally the higher the state of engine tune (more power from a smaller engine) the more damage is produced by cam belt failure. Modern engines are more likely to suffer serious damage than early designs.

If you do not know the vehicle history, replace the cam belt. Failure of this belt could cost you your engine!

Vehicle Faults

For many people the garage workshop is somewhere only visited when the vehicle has a problem. The vehicle performance may become poor, oil leaks develop and intermittent problems reduce driving comfort to a state that forces professional maintenance.

The spaghetti that exists under a modern vehicle bonnet is, hydraulic, pneumatic, electrical and electronic controls, employed on both diesel and petrol vehicles. All these controls operate a puzzle of plumbing which maintains the vehicle operating parameters within very tight limits.

When you require the professional services of a motor technician remember that a crystal ball is not part of the tool box. Try to make a note of any fault symptoms and the vehicle conditions when they occur:

· Engine temperature, from the gauge if you have one

· Engine speed

· Engine noise

· Weather conditions, wet, dry, frost

· Does the radio crackle

· Any help is better than nothing.

Many technicians are unfairly criticised because a customer will enter the service bay and ask for an electronic engine tune, failing to advise the technician that there is an intermittent fault with the vehicle. Then when the diagnostic service is complete and the fault was not present during the test, the customer is given a bill and drives off only to find that the fault re-occurs.

If you have a fault own up to it and try to help the technician with all the information available relating to the problem, saving time and money.


Diesel or Petrol

When fuel is burnt the gasses in the engine combustion chamber are heated and expand very rapidly to force the engine piston down, on its power stroke.

The volume or space into which the burn starts is very significant. A small volume will produce a greater pressure (for the same amount of fuel) and as the volume is less there will be less heat loss to the sides of the combustion chamber.

As the burning gas expands and forces down the piston, the volume around the piston increases. The expanding gas comes into contact with the relatively cool engine metalwork and cools. This cooling effect is a loss of energy, not transferred to power and reduces engine efficiency.

When the process is compared between petrol and diesel engines, the diesel engine will always be more efficient for comparative levels of technology.


In a diesel engine the volume into which fuel starts to burn is substantially smaller than the volume found in a petrol engine of the same capacity (cc's or litres volume). If the combustion process starts in a smaller volume of combustion chamber, there is less surface area for heat to be lost to the engine walls. More fuel is used to generate movement and less is lost in wasted heat.

If you care about the environment you will drive a small diesel vehicle.

 There are many very good web sites which provide a quality helpful information. This is one chosen to describe engine operation.



Multiplex Network Systems

We are now beginning to see the problems created due to the ignorance of multiplex wiring systems or vehicle networks.

Gone are the days when you can chop out or add in bits of electrical circuit.

YES it may have a wire going to it.

NO it does not go to the switch you may expect.

Vehicles built from 2000 will start to incorporate multiplex wiring systems.

What is a multiplex wiring system?

The vehicle normally has a pair of communication cables running around the body, stopping off at termination boxes. This is similar to a street of houses having telephone lines connected to each house. Each termination is capable of handling a huge amount of data, ask your pc.

For example when you move a light switch the light comes on. The light switch will send a message down the data cable to a switch station. The switch station is typically a body controller module behind the dash board. This controller will consider the request, to operate a light, then output the corresponding signal to a relay operating the light.

This simple example is duplicated for all the vehicles electric, that is everything in the car, everything under the bonnet, transmission, braking, traction control air conditioning the list goes on…...

The body controller is continually monitoring everything. Should you try to swap, modify, remove, anything with a wire to it, the body controller will find out and at best log a fault code. If you really upset the controller it will throw a mega strop and your car will not start. You will be off to an expert centre in your area to correct the fault.


Over the past 20 years vehicle electronics and associated diagnostics have evolved.

The 1980’s saw the start of electronic communication and the ability of a vehicle computer to produce fault codes in an effort to assist diagnostics.

During the 1990’s serial data became common and diagnostic kit was made available to read data such as injection duration and ignition timing.

Later came the ability to monitor systems, correct them and advise of the computers correction factors, such as fuelling requirements.

From around 2000, in an effort to stop vehicle theft, items were coded. Before systems will operate happily they require a hand shake with the vehicles electronic code. Radios will not work if they can not shake the hand of the master computer or Body Control computer when switched on. The ignition key needs a hand shake before the vehicle will start. Many vehicle components have the same requirement.

¤ Basic diagnostic kit can read fault codes.

¤ Most kit can read running date

¤ Better quality kit can interrogate vehicle correction factors for things like fuelling adjustments.

¤ Quality kit may be able to put out service lights and have a conversation with the Body Controller.

¤ Dealer level diagnostic kit can do everything including security checks, code keys and programme all other electrical components to the Body Controller.

Some independent garages have the top level kit and can offer you a main dealer service for diagnostics.

If you want to know about vehicle networks try the following links:

Information from Bosch

AVC-LAN system Audio Visual Communication

Testing the CAN Databus

BEAN Body Electronic Area Network

and more:

Other useful links


How engines work

How the Differential works

How the Clutch works

How the Gearbox works

How the Exhaust Gas & Emissions

Tyres Size and Pressure

There are many very good web sites which provide a quality helpful information. These are chosen to provide more detail for your.

Hope you enjoy it. 


Identifying vehicle problems since 1983.

Your car deserves specialist treatment! From check-ups to engine transplants, There are few independent garages which can support their customers with manufacturer’s genuine computer interrogation systems. Pratt’s have the dedicated computer systems for the Citroën, Peugeot and Renault ranges and top  aftermarket serial code readers for most other manufacturers.

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